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Red Hat Enterprise Linux 6

Virtualization Guide

Guide to Virtualization on Red Hat Enterprise Linux 6

Edition 1

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Abstract
The Red Hat Enterprise Linux Virtualization Guide contains information on installation, configuring, administering, and troubleshooting virtualization technologies included with Red Hat Enterprise Linux.

Preface
1. Document Conventions
1.1. Typographic Conventions
1.2. Pull-quote Conventions
1.3. Notes and Warnings
2. We need your feedback
1. Introduction
1.1. What is virtualization?
1.2. KVM and virtualization in Red Hat Enterprise Linux
1.3. libvirt and the libvirt tools
1.4. Virtualized hardware devices
1.4.1. Virtualized and emulated devices
1.4.2. Para-virtualized drivers
1.4.3. Physically shared devices
1.5. Storage
1.6. Virtualization security features
1.7. Migration
1.8. V2V
I. Requirements and limitations
2. System requirements
3. KVM compatibility
4. Virtualization limitations
4.1. General limitations for virtualization
4.2. KVM limitations
4.3. Application limitations
II. Installation
5. Installing the virtualization packages
5.1. Installing KVM with a new Red Hat Enterprise Linux installation
5.2. Installing KVM packages on an existing Red Hat Enterprise Linux system
6. Virtualized guest installation overview
6.1. Virtualized guest prerequisites and considerations
6.2. Creating guests with virt-install
6.3. Creating guests with virt-manager
6.4. Installing guests with PXE
7. Installing Red Hat Enterprise Linux 6 as a virtualized guest
7.1. Creating a Red Hat Enterprise Linux 6 guest with local installation media
7.2. Creating a Red Hat Enterprise Linux 6 guest with a network installation tree
7.3. Creating a Red Hat Enterprise Linux 6 guest with PXE
8. Installing Red Hat Enterprise Linux 6 as a para-virtualized guest on Red Hat Enterprise Linux 5
8.1. Using virt-install
8.2. Using virt-manager
9. Installing a fully-virtualized Windows guest
9.1. Using virt-install to create a guest
9.2. Installing Windows 2003
III. Configuration
10. Network Configuration
10.1. Network Address Translation (NAT) with libvirt
10.2. Bridged networking with libvirt
11. KVM Para-virtualized Drivers
11.1. Using the para-virtualized drivers with Red Hat Enterprise Linux 3.9 guests
11.2. Installing the KVM Windows para-virtualized drivers
11.2.1. Installing the drivers on an installed Windows guest
11.2.2. Installing drivers during the Windows installation
11.3. Using KVM para-virtualized drivers for existing devices
11.4. Using KVM para-virtualized drivers for new devices
12. PCI passthrough
12.1. Adding a PCI device with virsh
12.2. Adding a PCI device with virt-manager
12.3. PCI passthrough with virt-install
13. SR-IOV
13.1. Introduction
13.2. Using SR-IOV
13.3. Troubleshooting SR-IOV
14. KVM guest timing management
IV. Administration
15. Server best practices
16. Security for virtualization
16.1. Storage security issues
16.2. SELinux and virtualization
16.3. SELinux
16.4. Virtualization firewall information
17. sVirt
17.1. Security and Virtualization
17.2. sVirt labeling
18. KVM live migration
18.1. Live migration requirements
18.2. Shared storage example: NFS for a simple migration
18.3. Live KVM migration with virsh
18.4. Migrating with virt-manager
19. Remote management of virtualized guests
19.1. Remote management with SSH
19.2. Remote management over TLS and SSL
19.3. Transport modes
20. Overcommitting with KVM
21. KSM
22. Advanced virtualization administration
22.1. Guest scheduling
22.2. Advanced memory management
22.3. Guest block I/O throttling
22.4. Guest network I/O throttling
23. Migrating to KVM from other hypervisors using virt-v2v
23.1. Preparing to convert a virtualized guest
23.2. Converting virtualized guests
23.2.1. virt-v2v
23.2.2. Converting a local Xen virtualized guest
23.2.3. Converting a remote Xen virtualized guest
23.2.4. Converting a VMware ESX virtualized guest
23.2.5. Converting a virtualized guest running Windows
23.3. Running converted virtualized guests
23.4. Configuration changes
23.4.1. Configuration changes for Linux virtualized guests
23.4.2. Configuration changes for Windows virtualized guests
24. Miscellaneous administration tasks
24.1. Automatically starting guests
24.2. Using qemu-img
24.3. Verifying virtualization extensions
24.4. Setting KVM processor affinities
24.5. Generating a new unique MAC address
24.6. Improving guest response time
24.7. Very Secure ftpd
24.8. Disable SMART disk monitoring for guests
24.9. Configuring a VNC Server
24.10. Gracefully shutting down guests
24.11. Virtual machine timer management with libvirt
V. Virtualization storage topics
25. Storage concepts
25.1. Storage pools
25.2. Volumes
26. Storage pools
26.1. Creating storage pools
26.1.1. Dedicated storage device-based storage pools
26.1.2. Partition-based storage pools
26.1.3. Directory-based storage pools
26.1.4. LVM-based storage pools
26.1.5. iSCSI-based storage pools
26.1.6. NFS-based storage pools
27. Volumes
27.1. Creating volumes
27.2. Cloning volumes
27.3. Adding storage devices to guests
27.3.1. Adding file based storage to a guest
27.3.2. Adding hard drives and other block devices to a guest
27.4. Deleting and removing volumes
28. Miscellaneous storage topics
28.1. Creating a virtualized floppy disk controller
28.2. Configuring persistent storage in Red Hat Enterprise Linux 6
28.3. Accessing data from a guest disk image
29. N_Port ID Virtualization (NPIV)
29.1. Enabling NPIV on the switch
29.1.1. Identifying HBAs in a Host System
29.1.2. Verify NPIV is used on the HBA
VI. Virtualization reference guide
30. Managing guests with virsh
31. Managing guests with the Virtual Machine Manager (virt-manager)
31.1. Starting virt-manager
31.2. The Virtual Machine Manager main window
31.3. The virtual hardware details window
31.4. Virtual Machine graphical console
31.5. Adding a remote connection
31.6. Displaying guest details
31.7. Performance monitoring
31.8. Displaying CPU usage
31.9. Displaying Disk I/O
31.10. Displaying Network I/O
31.11. Managing a virtual network
31.12. Creating a virtual network
32. libvirt configuration reference
33. Creating custom libvirt scripts
33.1. Using XML configuration files with virsh
VII. Troubleshooting
34. Troubleshooting
34.1. Debugging and troubleshooting tools
34.2. kvm_stat
34.3. Log files
34.4. Troubleshooting with serial consoles
34.5. Virtualization log files
34.6. Loop device errors
34.7. Enabling Intel VT and AMD-V virtualization hardware extensions in BIOS
34.8. KVM networking performance
A. Additional resources
A.1. Online resources
A.2. Installed documentation
Glossary
B. Revision History
C. Colophon

Preface

Welcome to the Red Hat Enterprise Linux 6 Virtualization Guide. This guide covers all aspects of using and managing virtualization products included with Red Hat Enterprise Linux 6.
This book is divided into 7 parts:
  • System Requirements
  • Installation
  • Configuration
  • Administration
  • Reference
  • Troubleshooting
  • Appendixes
Key terms and concepts used throughout this book are covered in the Glossary.

1. Document Conventions

This manual uses several conventions to highlight certain words and phrases and draw attention to specific pieces of information.
In PDF and paper editions, this manual uses typefaces drawn from the Liberation Fonts set. The Liberation Fonts set is also used in HTML editions if the set is installed on your system. If not, alternative but equivalent typefaces are displayed. Note: Red Hat Enterprise Linux 5 and later includes the Liberation Fonts set by default.

1.1. Typographic Conventions

Four typographic conventions are used to call attention to specific words and phrases. These conventions, and the circumstances they apply to, are as follows.
Mono-spaced Bold
Used to highlight system input, including shell commands, file names and paths. Also used to highlight keycaps and key combinations. For example:
To see the contents of the file my_next_bestselling_novel in your current working directory, enter the cat my_next_bestselling_novel command at the shell prompt and press Enter to execute the command.
The above includes a file name, a shell command and a keycap, all presented in mono-spaced bold and all distinguishable thanks to context.
Key combinations can be distinguished from keycaps by the hyphen connecting each part of a key combination. For example:
Press Enter to execute the command.
Press Ctrl+Alt+F2 to switch to the first virtual terminal. Press Ctrl+Alt+F1 to return to your X-Windows session.
The first paragraph highlights the particular keycap to press. The second highlights two key combinations (each a set of three keycaps with each set pressed simultaneously).
If source code is discussed, class names, methods, functions, variable names and returned values mentioned within a paragraph will be presented as above, in mono-spaced bold. For example:
File-related classes include filesystem for file systems, file for files, and dir for directories. Each class has its own associated set of permissions.
Proportional Bold
This denotes words or phrases encountered on a system, including application names; dialog box text; labeled buttons; check-box and radio button labels; menu titles and sub-menu titles. For example:
Choose SystemPreferencesMouse from the main menu bar to launch Mouse Preferences. In the Buttons tab, click the Left-handed mouse check box and click Close to switch the primary mouse button from the left to the right (making the mouse suitable for use in the left hand).
To insert a special character into a gedit file, choose ApplicationsAccessoriesCharacter Map from the main menu bar. Next, choose SearchFind… from the Character Map menu bar, type the name of the character in the Search field and click Next. The character you sought will be highlighted in the Character Table. Double-click this highlighted character to place it in the Text to copy field and then click the Copy button. Now switch back to your document and choose EditPaste from the gedit menu bar.
The above text includes application names; system-wide menu names and items; application-specific menu names; and buttons and text found within a GUI interface, all presented in proportional bold and all distinguishable by context.
Mono-spaced Bold Italic or Proportional Bold Italic
Whether mono-spaced bold or proportional bold, the addition of italics indicates replaceable or variable text. Italics denotes text you do not input literally or displayed text that changes depending on circumstance. For example:
To connect to a remote machine using ssh, type ssh username@domain.name at a shell prompt. If the remote machine is example.com and your username on that machine is john, type ssh [email protected].
The mount -o remount file-system command remounts the named file system. For example, to remount the /home file system, the command is mount -o remount /home.
To see the version of a currently installed package, use the rpm -q package command. It will return a result as follows: package-version-release.
Note the words in bold italics above — username, domain.name, file-system, package, version and release. Each word is a placeholder, either for text you enter when issuing a command or for text displayed by the system.
Aside from standard usage for presenting the title of a work, italics denotes the first use of a new and important term. For example:
Publican is a DocBook publishing system.

1.2. Pull-quote Conventions

Terminal output and source code listings are set off visually from the surrounding text.
Output sent to a terminal is set in mono-spaced roman and presented thus:
books        Desktop   documentation  drafts  mss    photos   stuff  svn
books_tests  Desktop1  downloads      images  notes  scripts  svgs
Source-code listings are also set in mono-spaced roman but add syntax highlighting as follows:
package org.jboss.book.jca.ex1;

import javax.naming.InitialContext;

public class ExClient
{
   public static void main(String args[]) 
       throws Exception
   {
      InitialContext iniCtx = new InitialContext();
      Object         ref    = iniCtx.lookup("EchoBean");
      EchoHome       home   = (EchoHome) ref;
      Echo           echo   = home.create();

      System.out.println("Created Echo");

      System.out.println("Echo.echo('Hello') = " + echo.echo("Hello"));
   }
}

1.3. Notes and Warnings

Finally, we use three visual styles to draw attention to information that might otherwise be overlooked.

Note

Notes are tips, shortcuts or alternative approaches to the task at hand. Ignoring a note should have no negative consequences, but you might miss out on a trick that makes your life easier.

Important

Important boxes detail things that are easily missed: configuration changes that only apply to the current session, or services that need restarting before an update will apply. Ignoring a box labeled 'Important' will not cause data loss but may cause irritation and frustration.

Warning

Warnings should not be ignored. Ignoring warnings will most likely cause data loss.

2. We need your feedback

If you find a typographical error in this manual, or if you have thought of a way to make this manual better, we would love to hear from you. Submit a report in Bugzilla: http://bugzilla.redhat.com/ against the Red_Hat_Enterprise_Linux product.
When submitting a bug report, be sure to refer to the correct component: doc-Virtualization_Guide and version number: 6.
If you have a suggestion for improving the documentation, try to be as specific as possible when describing it. If you have found an error, include the section number and some of the surrounding text so we can find it easily.

Chapter 1. Introduction

This chapter introduces various virtualization technologies, applications and features and explains how they work. The purpose of this chapter is to assist Red Hat Enterprise Linux users in understanding the basics of virtualization.

1.1. What is virtualization?

Virtualization is a broad computing term for running software, usually operating systems, concurrently and isolated from other programs on one system. Most existing implementations of virtualization use a hypervisor, a software layer that controls hardware and provides guest operating systems with access to underlying hardware. The hypervisor allows multiple operating systems to run on the same physical system by offering virtualized hardware to the guest operating system. There are various methods for virtualizing operating systems:
  • Hardware-assisted virtualization is the technique used for full virtualization with KVM.
  • Para-virtualization is a technique used by Xen to run Linux guests.
  • Software virtualization or emulation. Software virtualization uses binary translation and other emulation techniques to run unmodified operating systems. Software virtualization is significantly slower than hardware-assisted virtualization or para-virtualization. Software virtualization, using QEMU without KVM, is unsupported by Red Hat Enterprise Linux.

1.2. KVM and virtualization in Red Hat Enterprise Linux

What is KVM?
(KVM) is a Full virtualization solution for Linux on AMD64 and Intel 64 hardware. KVM is a Linux kernel module built for the standard Red Hat Enterprise Linux 6 kernel. KVM can run multiple, unmodified virtualized guest Windows and Linux operating systems.The KVM hypervisor in Red Hat Enterprise Linux is managed with the libvirt API and tools built for libvirt, virt-manager and virsh. Virtualized guests are run as Linux processes and threads which are controlled by these modules.
Red Hat Enterprise Linux KVM hypervisors can be managed by the Red Hat Enterprise Virtualization Manager as an alternative to the virsh and virt-manager tools.
The kvm package also contains Linux kernel modules which manage devices, memory and management APIs for the Hypervisor module itself.
This book covers virtualization topics for Red Hat Enterprise Linux 6. The Kernel based Virtual Machine (KVM) hypervisor is provided with Red Hat Enterprise Linux. The KVM hypervisor supports Full virtualization.
Overcommitting
The KVM hypervisor supports overcommitting virtualized CPUs and memory. Overcommitting means allocating more virtualized CPUs or memory than the available resources on the system. CPU overcommitting allows virtualized guests to run on fewer servers and in higher densities. Memory overcommitting allows hosts to utilize memory and virtual memory to increase guest densities.
For more information on overcommitting with KVM, refer to Chapter 20, Overcommitting with KVM.
KSM
Kernel SamePage Merging (KSM) is used by the KVM hypervisor to allow KVM guests to share identical memory pages. These shared pages are usually common libraries or other identical, high-use data. KSM allows for greater guest density of identical or similar guest operating systems by avoiding memory duplication.
For more information on KSM, refer to Chapter 21, KSM.

1.3. libvirt and the libvirt tools

Libvirt is a hypervisor-independent virtualization API that is able to interact with the virtualization capabilities of a range of operating systems.
libvirt provides a common, generic and stable layer to securely manage virtualized guests on a host. libvirt provides a common interface for managing local systems and networked hosts. libvirt provides all APIs required to provision, create, modify, monitor, control, migrate and stop virtualized guests if the hypervisor supports these operations. Although multiple hosts may be accessed with libvirt simultaneously, the APIs are limited to single node operations.
libvirt is designed as a building block for higher level management tools and applications. libvirt focuses on managing single hosts, with the exception of migration capabilities. libvirt provides APIs to enumerate, monitor and use the resources available on the managed node, including CPUs, memory, storage, networking and Non-Uniform Memory Access (NUMA) partitions. The management tools can be located on separate physical machines from the host using secure protocols.
Red Hat Enterprise Linux 6 supports libvirt and included libvirt-based tools as its default method for virtualization management.
libvirt is free software available under the GNU Lesser General Public License. The libvirt project aims to provide a long term stable C API. The libvirt Open Source project currently supports Xen, QEmu, KVM, LXC, OpenVZ, VirtualBox, OpenNebula, and VMware ESX. The Red Hat Enterprise Linux 6 libvirt package supports Xen on Red Hat Enterprise Linux 5 and KVM on Red Hat Enterprise Linux 5 and Red Hat Enterprise Linux 6.
virsh
The virsh command-line tool is built on the libvirt management API and operates as an alternative to the graphical virt-manager application. The virsh command can be used in read-only mode by unprivileged users or, with root access, full administration functionality. The virsh command is ideal for scripting virtualization administration.
The virsh command is included in the libvirt-client package.
virt-manager
virt-manager is a graphical desktop tool for managing virtualized guests. virt-manager can be used to perform virtualization administration, virtualized guest creation, migration and configuration tasks. virt-manager allows access to graphical guest consoles. virt-manager can view virtualized guests, host statistics, device information and performance graphs. virt-manager can manage the local hypervisor and remote hypervisors using the same interface and methods.

1.4. Virtualized hardware devices

Virtualization on Red Hat Linux 6 presents three distinct types of system devices to virtualized guests. The three types include:
  • Emulated software devices.
  • Para-virtualized devices.
  • Physically shared devices.
These hardware devices all appear as physically attached hardware devices to the virtualized guest but the device drivers work in different ways.

1.4.1. Virtualized and emulated devices

The KVM hypervisor implements many core devices for virtualized guests in software. These emulated hardware devices are crucial for virtualizing operating systems. This section is provided as an introduction to the emulated devices and emulated device drivers.
Emulated devices are virtual devices which exist entirely in software. The emulated devices do not require a real hardware device to back them.
Emulated drivers may use either a physical device or a virtual software device. Emulated drivers are a translation layer between the guest and the Linux kernel (which manages the source device). The device level instructions are completely translated by the KVM hypervisor. Any device, of the same type, recognized by the Linux kernel may be used as the backing source device for the emulated drivers.
Virtualized CPUs (VCPUs)
A system has a number of virtual CPUs (VCPUs) relative to the number of physical processor cores. The number of virtual CPUs is finite and represents the total number of virtual CPUs that can be assigned to guest virtual machines.
Emulated graphics devices
Two emulated graphics devices are provided. These devices can be connected to with the SPICE protocol or with VNC.
  • The ac97 device emulates a Cirrus CLGD 5446 PCI VGA card.
  • The vga device emulates a dummy VGA card with Bochs VESA extensions (hardware level, including all non-standard modes).
Emulated system components
Various core system components are emulated to provide basic system functions.
  • A Cirrus i440FX host PCI bridge.
  • PIIX3 PCI to ISA bridge.
  • A PS/2 mouse and keyboard.
  • An EvTouch USB Graphics Tablet.
  • A PCI UHCI USB controller and a virtualized USB hub.
  • A PCI and ISA network adapters.
  • Emulated serial ports.
Emulated sound devices
Two emulated sound devices are available:
  • The ac97 device emulates an Intel 82801AA AC97 Audio compatible sound card.
  • The es1370 device emulates an ENSONIQ AudioPCI ES1370 sound card.
Emulated network drivers
There are four emulated network drivers available for network devices:
  • The e1000 driver emulates an Intel E1000 network adaptor (Intel 82540EM, 82573L, 82544GC).
  • The ne2k_pci driver emulates a Novell NE2000 network adaptor.
  • The pcnet driver emulates an AMD Lance Am7990 network adaptor.
  • The rtl8139 driver emulates a Realtek 8139 network adaptor.
Emulated storage drivers
Storage devices and storage pools can use the emulated drivers to attach storage devices to virtualized guests. Alternatively, the para-virtualized drivers can be used.
Note that the storage drivers are not storage devices. The drivers are used to attach a backing storage device, file or storage pool volume to a virtualized guest. The backing storage device can be any supported type of storage device, file, or storage pool volume.
The emulated IDE driver
The KVM hypervisor provides two emulated PCI IDE interfaces. The emulated IDE driver can be used to attach any combination of up to four virtualized IDE hard disks or virtualized IDE CD-ROM drives to each virtualized guest. The emulated IDE driver is used for virtualized CD-ROM and DVD-ROM drives.
The emulated floppy disk drive driver
The emulated floppy disk drive driver is used for creating virtualized floppy drives.

1.4.2. Para-virtualized drivers

Para-virtualized drivers are device drivers that increase the I/O performance of virtualized guests.
Para-virtualized drivers decrease I/O latency and increase I/O throughput to near bare-metal levels. It is recommended to use the para-virtualized drivers for virtualized guests running I/O intensive applications.
The para-virtualized drivers must be installed on the guest operating system. By default, the para-virtualized drivers are included in Red Hat Enterprise Linux 4.7 and newer, Red Hat Enterprise Linux 5.4 and newer and Red Hat Enterprise Linux 6.0 and newer. The para-virtualized drivers must be manually installed on Windows guests. For more information on using the para-virtualized drivers refer to Chapter 11, KVM Para-virtualized Drivers.
Para-virtualized network driver
The para-virtualized network driver is a Red Hat branded virtual network device. The para-virtualized network driver can be used as the driver for existing network devices or new network devices for virtualized guests.
Para-virtualized block driver
The para-virtualized block driver is a driver for all storage devices supported by the hypervisor attached to the virtualized guest (except for floppy disk drives, which must be emulated).
The para-virtualized clock
Guests using the Time Stamp Counter (TSC) as a clock source may suffer timing issues.
KVM works around hosts that do not have a constant Time Stamp Counter by providing guests with a para-virtualized clock.
For more information on the para-virtualized clock refer to Chapter 14, KVM guest timing management.
The para-virtualized serial driver
The para-virtualized serial driver (virtio-serial) is a bytestream-oriented, character stream driver. The para-virtualized serial driver provides a simple communication interface between the host's user space and the guest's user space where networking is not available or unusable.
The balloon driver
The balloon driver allows guests to express to the hypervisor how much memory they require. The balloon driver allows the host to efficiently allocate memory to the guest and allow free memory to be allocated to other guests and processes.
Guests using the balloon driver can mark sections of the guest's RAM as not in use (balloon inflation). The hypervisor can free the memory and use the memory for other host processes or other guests on that host.
When the guest requires the freed memory again, the hypervisor can reallocate RAM to the guest (balloon deflation).

1.4.3. Physically shared devices

Certain hardware platforms allow virtualized guests to directly access various hardware devices and components. This process in virtualization is known as passthrough. Passthrough is known as device assignment in some of the KVM documentation and the KVM code.
PCI passthrough
The KVM hypervisor supports attaching PCI devices on the host system to virtualized guests. PCI passthrough allows guests to have exclusive access to PCI devices for a range of tasks. PCI passthrough allows PCI devices to appear and behave as if they were physically attached to the guest operating system.
Almost all PCI and PCI Express devices that support passthrough, except for graphics cards, can be directly attached to virtualized guests with PCI passthrough.
SR-IOV
SR-IOV (Single Root I/O Virtualization) is a standard for a type of PCI passthrough which natively shares a single device to multiple guests.
SR-IOV enables a Single Root Function (for example, a single Ethernet port), to appear as multiple, separate, physical devices. A physical device with SR-IOV capabilities can be configured to appear in the PCI configuration space as multiple functions, each device has its own configuration space complete with Base Address Registers (BARs).
SR-IOV uses two new PCI functions:
  • Virtualization-PF
  • Virtualization VF
For more information on SR-IOV, refer to Chapter 13, SR-IOV.
NPIV
N_Port ID Virtualization (NPIV) is a function available with some Fibre Channel devices. NPIV shares a single physical N_Port as multiple N_Port IDs. NPIV provides similar functionality for Host Bus Adaptors (HBAs) that SR-IOV provides for network interfaces. With NPIV, virtualized guests can be provided with a virtual Fibre Channel initiator to Storage Area Networks (SANs).
NPIV can provide high density virtualized environments with enterprise-level storage solutions.
For more information on NPIV, refer to Chapter 29, N_Port ID Virtualization (NPIV).

1.5. Storage

Storage for virtualized guests is abstracted from the physical storage used by the guest. Storage is attached to virtualized guests using the para-virtualized (Section 1.4.2, “Para-virtualized drivers”) or emulated block device drivers (Emulated storage drivers).
Storage pools
A storage pool is a file, directory, or storage device managed by libvirt for the purpose of providing storage to virtualized guests. Storage pools are divided into storage volumes that store virtualized guest images or are attached to virtualized guests as additional storage.
Storage pools can be divided up into volumes or allocated directly to a guest. Volumes of a storage pool can be allocated to virtualized guests. There are two categories of storage pool available:
Local storage pools
Local storage pools are directly attached to the host server. Local storage pools include local directories, directly attached disks, and LVM volume groups on local devices.
Local storage pools are useful for development, testing and small deployments that do not require migration or large numbers of virtualized guests. Local storage pools are not suitable for many production environments as local storage pools do not support live migration.
Networked (shared) storage pools
Networked storage pools covers storage devices shared over a network using standard protocols.
Networked storage required for migrating guest virtualized guests between hosts. Networked storage pools are managed by libvirt.
Storage volumes
Storage pools are divided into storage volumes. Storage volumes are an abstraction of physical partitions, LVM logical volumes, file-based disk images and other storage types handled by libvirt. Storage volumes are presented to virtualized guests as local storage devices regardless of the underlying hardware.
For more information on storage and virtualization refer to Part V, “Virtualization storage topics”.

1.6. Virtualization security features

SELinux
SELinux was developed by the US National Security Agency and others to provide Mandatory Access Control (MAC) for Linux. All processes and files are given a type and access is limited by fine-grained controls. SELinux limits an attackers abilities and works to prevent many common security exploits such as buffer overflow attacks and privilege escalation.
SELinux strengthens the security model of Red Hat Enterprise Linux hosts and virtualized Red Hat Enterprise Linux guests. SELinux is configured and tested to work, by default, with all virtualization tools shipped with Red Hat Enterprise Linux 6.
For more information on SELinux and virtualization, refer to Section 16.2, “SELinux and virtualization”.
sVirt
sVirt is a technology included in Red Hat Enterprise Linux 6 that integrates SELinux and virtualization. sVirt applies Mandatory Access Control (MAC) to improve security when using virtualized guests. sVirt improves security and hardens the system against bugs in the hypervisor that might be used as an attack vector for the host or to another virtualized guest.
For more information on sVirt, refer to Chapter 17, sVirt.

1.7. Migration

Migration is the term for the process of moving a virtualized guest from one host to another. Migration can be conducted offline (where the guest is suspended and then moved) or live (where a guest is moved without suspending).
Migration is a key feature of virtualization as software is completely separated from hardware. Migration is useful for:
  • Load balancing - guests can be moved to hosts with lower usage when a host becomes overloaded.
  • Hardware failover - when hardware devices on the host start to fail, guests can be safely relocated so the host can be powered down and repaired.
  • Energy saving - guests can be redistributed to other hosts and host systems powered off to save energy and cut costs in low usage periods.
  • Geographic migration - guests can be moved to another location for lower latency or in serious circumstances.
Migration only moves the virtualized guest's memory. The guest's storage is located on networked storage which is shared between the source host and the destination.
Shared, networked storage must be used for storing guest images. Without shared storage migration is not possible. It is recommended to use libvirt managed storage pools for shared storage.
Offline migration
An offline migration suspends the guest then moves an image of the guest's memory to the destination host. The guest is resumed on the destination host and then memory the guest used on the source host is freed.
Live migration
Live migration is the process of migrating a running guest from one physical host to another physical host.
For more information on migration refer to Chapter 18, KVM live migration.

1.8. V2V

Virtualized to virtualized migration, known as V2V, is supported in Red Hat Enterprise Linux 6 for certain virtualized guests.
Red Hat Enterprise Linux 6 provides tools for converting virtualized guests from other types of hypervisor to KVM. The virt-v2v tool converts and imports virtual machines from Xen, other versions of KVM and VMware ESX.
For more information on using V2V, refer to Chapter 23, Migrating to KVM from other hypervisors using virt-v2v

Part I. Requirements and limitations

System requirements, support restrictions and limitations for virtualization with Red Hat Enterprise Linux 6

These chapters outline the system requirements, support restrictions, and limitations of virtualization on Red Hat Enterprise Linux 6.

Chapter 2. System requirements

This chapter lists system requirements for successfully running virtualized guest operating systems with Red Hat Enterprise Linux 6. Virtualization is available for Red Hat Enterprise Linux 6 on the Intel 64 and AMD64 architecture.
The KVM hypervisor is provided with Red Hat Enterprise Linux 6.
For information on installing the virtualization packages, read Chapter 5, Installing the virtualization packages.
Minimum system requirements
  • 6GB free disk space
  • 2GB of RAM.

KVM overcommit

KVM can overcommit physical resources for virtualized guests. Overcommitting resources means the total virtualized RAM and processor cores used by the guests can exceed the physical RAM and processor cores on the host. For information on safely overcommitting resources with KVM refer to Chapter 20, Overcommitting with KVM.
KVM requirements
The KVM hypervisor requires:
  • an Intel processor with the Intel VT and the Intel 64 extensions, or
  • an AMD processor with the AMD-V and the AMD64 extensions.
Refer to Section 24.3, “Verifying virtualization extensions” to determine if your processor has the virtualization extensions.
Storage support
The working guest storage methods are:
  • files on local storage,
  • physical disk partitions,
  • locally connected physical LUNs,
  • LVM partitions,
  • NFS shared file systems,
  • iSCSI,
  • GFS2 clustered file systems, and
  • Fibre Channel-based LUNs
  • SRP devices (SCSI RDMA Protocol), the block export protocol used in Infiniband and 10GbE iWARP adapters.

File-based guest storage

File-based guest images should be stored in the /var/lib/libvirt/images/ folder. If you use a different directory you must add the directory to the SELinux policy. Refer to Section 16.2, “SELinux and virtualization” for details.

Chapter 3. KVM compatibility

The KVM hypervisor requires a processor with the Intel-VT or AMD-V virtualization extensions.
Note that this list is not complete. Help us expand it by sending in a bug with anything you get working.
To verify whether your processor supports the virtualization extensions and for information on enabling the virtualization extensions if they are disabled, refer to Section 24.3, “Verifying virtualization extensions”.
Red Hat Enterprise Linux 6.0 Servers with the kvm package are limited to 256 processor cores or less.
Supported guests
Operating systemSupport level
Red Hat Enterprise Linux 3 x86Optimized with para-virtualized drivers
Red Hat Enterprise Linux 4 x86Optimized with para-virtualized drivers
Red Hat Enterprise Linux 4 AMD 64 and Intel 64Optimized with para-virtualized drivers
Red Hat Enterprise Linux 5 x86Optimized with para-virtualized drivers
Red Hat Enterprise Linux 5 AMD 64 and Intel 64Optimized with para-virtualized drivers
Red Hat Enterprise Linux 6 x86Optimized with para-virtualized drivers
Red Hat Enterprise Linux 6 AMD 64 and Intel 64Optimized with para-virtualized drivers
Fedora 12 x86Optimized with para-virtualized drivers
Fedora 12 AMD 64 and Intel 64Optimized with para-virtualized drivers
Fedora 13 x86Optimized with para-virtualized drivers
Fedora 13 AMD 64 and Intel 64Optimized with para-virtualized drivers
Windows Server 2003 R2 32-BitOptimized with para-virtualized drivers
Windows Server 2003 R2 64-BitOptimized with para-virtualized drivers
Windows Server 2003 Service Pack 2 32-BitOptimized with para-virtualized drivers
Windows Server 2003 Service Pack 2 64-BitOptimized with para-virtualized drivers
Windows XP 32-BitOptimized with para-virtualized drivers
Windows Vista 32-BitSupported
Windows Vista 64-BitSupported
Windows Server 2008 32-BitOptimized with para-virtualized drivers
Windows Server 2008 (and R2) 64-BitOptimized with para-virtualized drivers
Windows 7 32-BitOptimized with para-virtualized drivers
Windows 7 64-BitOptimized with para-virtualized drivers

Chapter 4. Virtualization limitations

This chapter covers additional support and product limitations of the virtualization packages in Red Hat Enterprise Linux 6.

4.1. General limitations for virtualization

Other limitations
For the list of all other limitations and issues affecting virtualization read the Red Hat Enterprise Linux 6 Release Notes. The Red Hat Enterprise Linux 6 Release Notes cover the present new features, known issues and limitations as they are updated or discovered.
Test before deployment
You should test for the maximum anticipated load and virtualized network stress before deploying heavy I/O applications. Stress testing is important as there are performance drops caused by virtualization with increased I/O usage.

4.2. KVM limitations

The following limitations apply to the KVM hypervisor:
Maximum VCPUs per guest
Virtualized guests support up to a maximum of 64 virtualized CPUs in Red Hat Enterprise Linux 6.0.
Constant TSC bit
Systems without a Constant Time Stamp Counter require additional configuration. Refer to Chapter 14, KVM guest timing management for details on determining whether you have a Constant Time Stamp Counter and configuration steps for fixing any related issues.
Memory overcommit
KVM supports memory overcommit and can store the memory of guests in swap. A guest will run slower if it is swapped frequently. When KSM is used, make sure that the swap size is the size of the overcommit ratio.
CPU overcommit
It is not recommended to have more than 10 virtual CPUs per physical processor core. Any number of overcommitted virtual CPUs above the number of physical processor cores may cause problems with certain virtualized guests.
Overcommitting CPUs has some risk and can lead to instability. Refer to Chapter 20, Overcommitting with KVM for tips and recommendations on overcommitting CPUs.
Virtualized SCSI devices
SCSI emulation is limited to 16 virtualized (emulated) SCSI devices..
Virtualized IDE devices
KVM is limited to a maximum of four virtualized (emulated) IDE devices per guest.
Para-virtualized devices
Para-virtualized devices, which use the virtio drivers, are PCI devices. Presently, guests are limited to a maximum of 32 PCI devices. Some PCI devices are critical for the guest to run and these devices cannot be removed. The default, required devices are:
  • the host bridge,
  • the ISA bridge and usb bridge (The usb and isa bridges are the same device),
  • the graphics card (using either the Cirrus or qxl driver), and
  • the memory balloon device.
Out of the 32 available PCI devices for a guest 4 are not removable. This means there are only 28 PCI slots available for additional devices per guest. Every para-virtualized network or block device uses one slot. Each guest can use up to 28 additional devices made up of any combination of para-virtualized network, para-virtualized disk devices, or other PCI devices using VT-d.
Migration limitations
Live migration is only possible with CPUs from the same vendor (that is, Intel to Intel or AMD to AMD only).
The No eXecution (NX) bit must be set to on or off for both CPUs for live migration.
Storage limitations
The host should not use disk labels to identify file systems in the fstab file, the initrd file or used by the kernel command line. If less privileged users, especially virtualized guests, have write access to whole partitions or LVM volumes the host system could be compromised.
Guest should not be given write access to whole disks or block devices (for example, /dev/sdb). Virtualized guests with access to block devices may be able to access other block devices on the system or modify volume labels which can be used to compromise the host system. Use partitions (for example, /dev/sdb1) or LVM volumes to prevent this issue.
SR-IOV limitations
SR-IOV is only supported with the following devices:
Intel® 82576NS Gigabit Ethernet Controller (igb driver)
Intel® 82576EB Gigabit Ethernet Controller (igb driver)
Neterion X3100 Series 10GbE PCIe (vxge driver)
Intel® 82599ES 10 Gigabit Ethernet Controller (ixgbe driver)
Intel® 82599EB 10 Gigabit Ethernet Controller (ixgbe driver)
PCI passthrough limitations
PCI passthrough (attaching PCI devices to guests) should work on systems with the AMD IOMMU or Intel VT-d technologies.

4.3. Application limitations

There are aspects of virtualization which make virtualization unsuitable for certain types of applications.
Applications with high I/O throughput requirements should use the para-virtualized drivers for fully virtualized guests. Without the para-virtualized drivers certain applications may be unstable under heavy I/O loads.
The following applications should be avoided for their high I/O requirement reasons:
  • kdump server
  • netdump server
You should carefully evaluate databasing applications before running them on a virtualized guest. Databases generally use network and storage I/O devices intensively. These applications may not be suitable for a fully virtualized environment. Consider the para-virtualized drivers or PCI passthrough for increased I/O performance. Refer to Chapter 11, KVM Para-virtualized Drivers for more information on the para-virtualized drivers for fully virtualized guests. Refer to Chapter 12, PCI passthrough for more information on the PCI passthrough.
Other applications and tools which heavily utilize I/O or require real-time performance should be evaluated carefully. Using full virtualization with the para-virtualized drivers (refer to Chapter 11, KVM Para-virtualized Drivers) or PCI passthrough (refer to Chapter 12, PCI passthrough) results in better performance with I/O intensive applications. Applications still suffer a small performance loss from running in virtualized environments. The performance benefits of virtualization through consolidating to newer and faster hardware should be evaluated against the potential application performance issues associated with using virtualization.

Part II. Installation

Chapter 5. Installing the virtualization packages

Before you can use virtualization, the virtualization packages must be installed on your computer. Virtualization packages can be installed either during the installation sequence or after installation using the yum command and the Red Hat Network (RHN).
The KVM hypervisor uses the default Red Hat Enterprise Linux kernel with the kvm kernel module.

5.1. Installing KVM with a new Red Hat Enterprise Linux installation

This section covers installing virtualization tools and KVM package as part of a fresh Red Hat Enterprise Linux installation.

Need help installing?

The Installation Guide (available from redhat.com) covers installing Red Hat Enterprise Linux in detail.
  1. Start an interactive Red Hat Enterprise Linux installation from the Red Hat Enterprise Linux Installation CD-ROM, DVD or PXE.
  2. You must enter a valid installation number when prompted to receive access to the virtualization and other Advanced Platform packages.
  3. Complete the other steps up to the package selection step.
    Select the Virtual Host server role to install a platform for virtualized guests. Alternatively, select the Customize Now radio button to specify individual packages.
  4. Select the Virtualization package group. This selects the KVM hypervisor, virt-manager, libvirt and virt-viewer for installation.
  5. Customize the packages (if required)

    Customize the Virtualization group if you require other virtualization packages.
    Press the Close button then the Next button to continue the installation.

Note

You require a valid RHN virtualization entitlement to receive updates for the virtualization packages.
Installing KVM packages with Kickstart files
This section describes how to use a Kickstart file to install Red Hat Enterprise Linux with the KVM hypervisor packages. Kickstart files allow for large, automated installations without a user manually installing each individual system. The steps in this section will assist you in creating and using a Kickstart file to install Red Hat Enterprise Linux with the virtualization packages.
In the %packages section of your Kickstart file, append the following package group:
%packages
@kvm
More information on Kickstart files can be found on Red Hat's website, redhat.com, in the Installation Guide.

5.2. Installing KVM packages on an existing Red Hat Enterprise Linux system

The section describes the steps for installing the KVM hypervisor on a working Red Hat Enterprise Linux 6 or newer system.
Adding packages to your list of Red Hat Network entitlements
This section describes how to enable Red Hat Network (RHN) entitlements for the virtualization packages. You need these entitlements enabled to install and update the virtualization packages on Red Hat Enterprise Linux. You require a valid Red Hat Network account in order to install virtualization packages on Red Hat Enterprise Linux.
In addition, your machines must be registered with RHN. To register an unregistered installation of Red Hat Enterprise Linux, run the rhn_register command and follow the prompts.
If you do not have a valid Red Hat subscription, visit the Red Hat online store.
Procedure 5.1. Adding the Virtualization entitlement with RHN
  1. Log in to RHN using your RHN username and password.
  2. Select the systems you want to install virtualization on.
  3. In the System Properties section the present systems entitlements are listed next to the Entitlements header. Use the (Edit These Properties) link to change your entitlements.
  4. Select the Virtualization checkbox.
Your system is now entitled to receive the virtualization packages. The next section covers installing these packages.
Installing the KVM hypervisor with yum
To use virtualization on Red Hat Enterprise Linux you require the kvm package. The kvm package contains the KVM kernel module providing the KVM hypervisor on the default Red Hat Enterprise Linux kernel.
To install the kvm package, run:
# yum install kvm
Now, install additional virtualization management packages.
Install the other recommended virtualization packages:
# yum install virt-manager libvirt libvirt-python python-virtinst libvirt-client

Chapter 6. Virtualized guest installation overview

After you have installed the virtualization packages on the host system you can create guest operating systems. This chapter describes the general processes for installing guest operating systems on virtual machines. You can create guests using the New button in virt-manager or use the command line interface virt-install. Both methods are covered by this chapter.
Detailed installation instructions are available for specific versions of Red Hat Enterprise Linux, other Linux distributions, Solaris and Windows. Refer to the relevant procedure for you guest operating system:

6.1. Virtualized guest prerequisites and considerations

Various factors should be considered before creating any virtualized guests. Factors include:
  • Performance
  • Input/output requirements and types of input/output.
  • Storage.
  • Networking and network infrastructure.
  • Guest load and usage for processor and memory resources.

6.2. Creating guests with virt-install

You can use the virt-install command to create virtualized guests from the command line. virt-install is used either interactively or as part of a script to automate the creation of virtual machines. Using virt-install with Kickstart files allows for unattended installation of virtual machines.
The virt-install tool provides a number of options one can pass on the command line. To see a complete list of options run:
$ virt-install --help
The virt-install man page also documents each command option and important variables.
qemu-img is a related command which may be used before virt-install to configure storage options.
An important option is the --vnc option which opens a graphical window for the guest's installation.
Example 6.1. Using virt-install to install a RHEL 5 guest
This example creates a RHEL 5 guest with the following settings:
  • Uses LVM partitioning
  • Is a plain QEMU guest
  • Uses virtual networking
  • Boots from PXE
  • Uses VNC server/viewer
# virt-install \
   --network network:default \
   --name rhel5support --ram=756\
   --file=/var/lib/libvirt/images/rhel5support.img \
   --file-size=6 --vnc --cdrom=/dev/sr0

Refer to man virt-install for more examples.

6.3. Creating guests with virt-manager

virt-manager, also known as Virtual Machine Manager, is a graphical tool for creating and managing virtualized guests.
Procedure 6.1. Creating a virtualized guest with virt-manager
  1. Open virt-manager

    Start virt-manager. Launch the Virtual Machine Manager application from the Applications menu and System Tools submenu. Alternatively, run the virt-manager command as root.
  2. Optional: Open a remote hypervisor

    Select the hypervisor and press the Connect button to connect to the remote hypervisor.
  3. Create a new guest

    The virt-manager window allows you to create a new virtual machine. Click the New button (Figure 6.1, “Virtual Machine Manager window”) to open the New VM wizard.
    Virtual Machine Manager window
    Figure 6.1. Virtual Machine Manager window

  4. New VM wizard

    The New VM wizard breaks down the guest creation process into five steps:
    1. Naming the guest and choosing the installation type
    2. Locating and configuring the installation media
    3. Configuring memory and CPU options
    4. Configuring the guest's storage
    5. Configuring networking, hypervisor type, architecture, and other hardware settings
    Ensure that virt-manager can access the installation media (whether locally or over the network).
  5. Specify name and installation type

    The guest creation process starts with the selection of a name and installation type. Virtual machine names can have underscores (_), periods (.), and hyphens (-).
    Step 1
    Figure 6.2. Step 1

    Type in a virtual machine name and choose an installation type:
    Local install media (ISO image or CDROM)
    This method uses a CD-ROM, DVD, or image of an installation disk (e.g. .iso).
    Network Install (HTTP, FTP, or NFS)
    Network installing involves the use of a mirrored Red Hat Enterprise Linux or Fedora installation tree to install a guest. The installation tree must be accessible through either HTTP, FTP, or NFS.
    Network Boot (PXE)
    This method uses a Preboot eXecution Environment (PXE) server to install the guest. Setting up a PXE server is covered in the Deployment Guide. To install via network boot, the guest must have a routable IP address or shared network device. For information on the required networking configuration for PXE installation, refer to Chapter 10, Network Configuration.
    Import existing disk image
    This method allows you to create a new guest and import a disk image (containing a pre-installed, bootable operating system) to it.
    Click Forward to continue.
  6. Configure installation

    Next, configure the OS type and Version of the installation. Except for network booting, this step also requires further configuration (depending on your chosen installation method). When using local install media or importing an existing disk image, you need to specify the location of the installation media or disk image.
    Local install media (configuration)
    Figure 6.3. Local install media (configuration)

    Import existing disk image (configuration)
    Figure 6.4. Import existing disk image (configuration)

    Important

    It is recommend that you use the default directory for virtual machine images, /var/lib/libvirt/images/. If you are using a different location, make sure it is added to your SELinux policy and relabeled before you continue with the installation. Refer to Section 16.2, “SELinux and virtualization” for details on how to do this.
    When performing a network install, you need to specify the URL of the installation tree. You can also specify the URL of any kickstart files you want to use, along with any kernel options you want to pass during installation.
    Network Install (configuration)
    Figure 6.5. Network Install (configuration)

    Click Forward to continue.
  7. Configure CPU and memory

    The next step involves configuring the number of CPUs and amount of memory to allocate to the virtual machine. The wizard shows the number of CPUs and amount of memory you can allocate; configure these settings and click Forward.
    Configuring CPU and Memory
    Figure 6.6. Configuring CPU and Memory

  8. Configure storage

    Assign a physical storage device (Block device) or a file-based image (File). File-based images should be stored in /var/lib/libvirt/images/ to satisfy default SELinux permissions.
    Configuring virtual storage
    Figure 6.7. Configuring virtual storage

    If you chose to import an existing disk image during the first step, virt-manager will skip this step.
    Assign sufficient space for your virtualized guest and any applications the guest requires, then click Forward to continue.
  9. Final configuration

    Verify the settings of the virtual machine and click Finish when you are satisfied; doing so will create the guest with default networking settings, virtualization type, and architecture.
    Verifying the configuration
    Figure 6.8. Verifying the configuration

    If you prefer to further configure the virtual machine's hardware first, check the Customize configuration before install box first before clicking Finish. Doing so will open another wizard Figure 6.9, “Virtual hardware configuration” that will allow you to add, remove, and configure the virtual machine's hardware settings.
    Virtual hardware configuration
    Figure 6.9. Virtual hardware configuration

    After configuring the virtual machine's hardware, click Apply. virt-manager will then create the guest with your specified hardware settings.
This concludes the general process for creating guests with virt-manager. Chapter 6, Virtualized guest installation overview contains step-by-step instructions to installing a variety of common operating systems.

6.4. Installing guests with PXE

This section covers the steps required to install guests with PXE. PXE guest installation requires a shared network device, also known as a network bridge. The procedures below covers creating a bridge and the steps required to utilize the bridge for PXE installation.
  1. Create a new bridge

    1. Create a new network script file in the /etc/sysconfig/network-scripts/ directory. This example creates a file named ifcfg-installation which makes a bridge named installation.
      # cd /etc/sysconfig/network-scripts/
      # vim ifcfg-installation
      DEVICE=installation
      TYPE=Bridge
      BOOTPROTO=dhcp
      ONBOOT=yes
      

      Warning

      The line, TYPE=Bridge, is case-sensitive. It must have uppercase 'B' and lower case 'ridge'.
    2. Start the new bridge by restarting the network service. The ifup installation command can start the individual bridge but it is safer to test the entire network restarts properly.
      # service network restart
      
    3. There are no interfaces added to the new bridge yet. Use the brctl show command to view details about network bridges on the system.
      # brctl show
      bridge name     bridge id               STP enabled     interfaces
      installation    8000.000000000000       no
      virbr0          8000.000000000000       yes
      
      The virbr0 bridge is the default bridge used by libvirt for Network Address Translation (NAT) on the default Ethernet device.
  2. Add an interface to the new bridge

    Edit the configuration file for the interface. Add the BRIDGE parameter to the configuration file with the name of the bridge created in the previous steps.
    # Intel Corporation Gigabit Network Connection
    DEVICE=eth1
    BRIDGE=installation
    BOOTPROTO=dhcp
    HWADDR=00:13:20:F7:6E:8E
    ONBOOT=yes
    
    After editing the configuration file, restart networking or reboot.
    # service network restart
    
    Verify the interface is attached with the brctl show command:
    # brctl show
    bridge name     bridge id               STP enabled     interfaces
    installation    8000.001320f76e8e       no              eth1
    virbr0          8000.000000000000       yes
    
  3. Security configuration

    Configure iptables to allow all traffic to be forwarded across the bridge.
    # iptables -I FORWARD -m physdev --physdev-is-bridged -j ACCEPT
    # service iptables save
    # service iptables restart
    

    Disable iptables on bridges

    Alternatively, prevent bridged traffic from being processed by iptables rules. In /etc/sysctl.conf append the following lines:
    net.bridge.bridge-nf-call-ip6tables = 0
    net.bridge.bridge-nf-call-iptables = 0
    net.bridge.bridge-nf-call-arptables = 0
    
    Reload the kernel parameters configured with sysctl.
    # sysctl -p /etc/sysctl.conf
    
  4. Restart libvirt before the installation

    Restart the libvirt daemon.
    # service libvirtd reload
    
The bridge is configured, you can now begin an installation.
PXE installation with virt-install
For virt-install append the --network=bridge:installation installation parameter where installation is the name of your bridge. For PXE installations use the --pxe parameter.
Example 6.2. PXE installation with virt-install
# virt-install --hvm --connect qemu:///system \
    --network=bridge:installation --pxe\
    --name EL10 --ram=756 \
    --vcpus=4
    --os-type=linux --os-variant=rhel5
    --file=/var/lib/libvirt/images/EL10.img \

PXE installation with virt-manager
The steps below are the steps that vary from the standard virt-manager installation procedures.
  1. Select PXE

    Select PXE as the installation method.
  2. Select the bridge

    Select Shared physical device and select the bridge created in the previous procedure.
  3. Start the installation

    The installation is ready to start.
A DHCP request is sent and if a valid PXE server is found the guest installation processes will start.

Chapter 7. Installing Red Hat Enterprise Linux 6 as a virtualized guest

This Chapter covers how to install Red Hat Enterprise Linux 6 as a fully virtualized guest on Red Hat Enterprise Linux 6.
This procedure assumes that the KVM hypervisor and all other required packages are installed and the host is configured for virtualization. For more information on installing the virtualization pacakges, refer to Chapter 5, Installing the virtualization packages.

7.1. Creating a Red Hat Enterprise Linux 6 guest with local installation media

This procedure covers creating a virtualized Red Hat Enterprise Linux 6 guest with a locally stored installation DVD or DVD image. DVD images are available from rhn.redhat.com for Red Hat Enterprise Linux 6.
Procedure 7.1. Creating a Red Hat Enterprise Linux 6 guest with virt-manager
  1. Optional: Preparation

    Prepare the storage environment for the virtualized guest. For more information on preparing storage, refer to Part V, “Virtualization storage topics”.

    Note

    Various storage types may be used for storing virtualized guests. However, for a guest to be able to use migration features the guest must be created on networked storage.
    Red Hat Enterprise Linux 6 requires at least 1GB of storage space. However, Red Hat recommends at least 5GB of storage space for a Red Hat Enterprise Linux 6 installation and for the procedures in this guide.
  2. Open virt-manager and start the wizard

    Open virt-manager by executing the virt-manager command as root or opening Applications -> System Tools -> Virtual Machine Manager.
    The main virt-manager window
    Figure 7.1. The main virt-manager window

    Press the create new virtualized guest button (see figure Figure 7.2, “The create new virtualized guest button”) to start the new virtualized guest wizard.
    The create new virtualized guest button
    Figure 7.2. The create new virtualized guest button

    The Create a new virtual machine window opens.
  3. Name the virtualized guest

    Guest names can contain letters, numbers and the following characters: '_', '.' and '-'. Guest names must be unique for migration.
    Choose the Local install media (ISO image or CDROM) radio button.
    The Create a new virtual machine window - Step 1
    Figure 7.3. The Create a new virtual machine window - Step 1

    Press Forward to continue.
  4. Select the installation media

    Select the installation ISO image location or a DVD drive with the installation disc inside. This example uses an ISO file image of the Red Hat Enterprise Linux 6.0 installation DVD image.
    The Locate ISO media volume window
    Figure 7.4. The Locate ISO media volume window

    Image files and SELinux

    For ISO image files and guest storage images, the recommended directory to use is the /var/lib/libvirt/images/ directory. Any other location may require additional configuration for SELinux, refer to Section 16.2, “SELinux and virtualization” for details.
    Select the operating system type and version which match the installation media you have selected.
    The Create a new virtual machine window - Step 2
    Figure 7.5. The Create a new virtual machine window - Step 2

    Press Forward to continue.
  5. Set RAM and virtual CPUs

    Choose appropriate values for the virtualized CPUs and RAM allocation. These values affect the host's and guest's performance. Memory and virtualized CPUs can be overcommitted, for more information on overcommitting refer to Chapter 20, Overcommitting with KVM.
    Virtualized guests require sufficient physical memory (RAM) to run efficiently and effectively. Red Hat supports a minimum of 512MB of RAM for a virtualized guest. Red Hat recommends at least 1024MB of RAM for each logical core.
    Assign sufficient virtual CPUs for the virtualized guest. If the guest runs a multithreaded application, assign the number of virtualized CPUs the guest will require to run efficiently.
    You cannot assign more virtual CPUs than there are physical processors (or hyper-threads) available on the host system. The number of virtual CPUs available is noted in the Up to X available field.
    The Create a new virtual machine window - Step 3
    Figure 7.6. The Create a new virtual machine window - Step 3

    Press Forward to continue.
  6. Storage

    Enable and assign storage for the Red Hat Enterprise Linux 6 guest. Assign at least 5GB for a desktop installation or at least 1GB for a minimal installation.

    Migration

    Live and offline migrations require guests to be installed on shared network storage. For information on setting up shared storage for guests refer to Part V, “Virtualization storage topics”.
    1. With the default local storage

      Select the Create a disk image on the computer's hard drive radio button to create a file-based image in the default storage pool, the /var/lib/libvirt/images/ directory. Enter the size of the disk image to be created. If the Allocate entire disk now check box is selected, a disk image of the size specified will be created immediately. If not, the disk image will grow as it becomes filled.
      The Create a new virtual machine window - Step 4
      Figure 7.7. The Create a new virtual machine window - Step 4

    2. With a storage pool

      Select Select managed or other existing storage to use a storage pool.
      The Locate or create storage volume window
      Figure 7.8. The Locate or create storage volume window

      1. Press the browse button to open the storage pool browser.
      2. Select a storage pool from the Storage Pools list.
      3. Optional: Press the New Volume button to create a new storage volume. Enter the name of the new storage volume.
      4. Press the Choose Volume button to select the volume for the virtualized guest.
      The Create a new virtual machine window - Step 4
      Figure 7.9. The Create a new virtual machine window - Step 4

    Press Forward to continue.
  7. Verify and finish

    Verify there were no errors made during the wizard and everything appears as expected.
    Select the Customize configuration before install check box to change the guest's storage or network devices, to use the para-virtualized drivers or, to add additional devices.
    Press the Advanced options down arrow to inspect and modify advanced options. For a standard Red Hat Enterprise Linux 6 none of these options require modification.
    The Create a new virtual machine window - Step 5
    Figure 7.10. The Create a new virtual machine window - Step 5

    Press Finish to continue into the Red Hat Enterprise Linux installation sequence. For more information on installing Red Hat Enterprise Linux 6 refer to the Red Hat Enterprise Linux 6 Installation Guide.
A Red Hat Enterprise Linux 6 guest is now created from a an ISO installation disc image.

7.2. Creating a Red Hat Enterprise Linux 6 guest with a network installation tree

Procedure 7.2. Creating a Red Hat Enterprise Linux 6 guest with virt-manager
  1. Optional: Preparation

    Prepare the storage environment for the virtualized guest. For more information on preparing storage, refer to Part V, “Virtualization storage topics”.

    Note

    Various storage types may be used for storing virtualized guests. However, for a guest to be able to use migration features the guest must be created on networked storage.
    Red Hat Enterprise Linux 6 requires at least 1GB of storage space. However, Red Hat recommends at least 5GB of storage space for a Red Hat Enterprise Linux 6 installation and for the procedures in this guide.
  2. Open virt-manager and start the wizard

    Open virt-manager by executing the virt-manager command as root or opening Applications -> System Tools -> Virtual Machine Manager.
    The main virt-manager window
    Figure 7.11. The main virt-manager window

    Press the create new virtualized guest button (see figure Figure 7.12, “The create new virtualized guest button”) to start the new virtualized guest wizard.
    The create new virtualized guest button
    Figure 7.12. The create new virtualized guest button

    The Create a new virtual machine window opens.
  3. Name the virtualized guest

    Guest names can contain letters, numbers and the following characters: '_', '.' and '-'. Guest names must be unique for migration.
    Choose the installation method from the list of radio buttons.
    The Create a new virtual machine window - Step 1
    Figure 7.13. The Create a new virtual machine window - Step 1

    Press Forward to continue.

7.3. Creating a Red Hat Enterprise Linux 6 guest with PXE

Procedure 7.3. Creating a Red Hat Enterprise Linux 6 guest with virt-manager
  1. Optional: Preparation

    Prepare the storage environment for the virtualized guest. For more information on preparing storage, refer to Part V, “Virtualization storage topics”.

    Note

    Various storage types may be used for storing virtualized guests. However, for a guest to be able to use migration features the guest must be created on networked storage.
    Red Hat Enterprise Linux 6 requires at least 1GB of storage space. However, Red Hat recommends at least 5GB of storage space for a Red Hat Enterprise Linux 6 installation and for the procedures in this guide.
  2. Open virt-manager and start the wizard

    Open virt-manager by executing the virt-manager command as root or opening Applications -> System Tools -> Virtual Machine Manager.
    The main virt-manager window
    Figure 7.14. The main virt-manager window

    Press the create new virtualized guest button (see figure Figure 7.15, “The create new virtualized guest button”) to start the new virtualized guest wizard.
    The create new virtualized guest button
    Figure 7.15. The create new virtualized guest button

    The Create a new virtual machine window opens.
  3. Name the virtualized guest

    Guest names can contain letters, numbers and the following characters: '_', '.' and '-'. Guest names must be unique for migration.
    Choose the installation method from the list of radio buttons.
    The Create a new virtual machine window - Step 1
    Figure 7.16. The Create a new virtual machine window - Step 1

    Press Forward to continue.

Chapter 8. Installing Red Hat Enterprise Linux 6 as a para-virtualized guest on Red Hat Enterprise Linux 5

This section describes how to install Red Hat Enterprise Linux 6 as a para-virtualized guest on Red Hat Enterprise Linux 5. Para-virtualization is only available for Red Hat Enterprise Linux 5 hosts. Red Hat Enterprise Linux 6 uses the PV-opts features of the Linux kernel to appear as a compatible Xen para-virtualized guest.

Important note on para-virtualization

Para-virtualization only works with the Xen hypervisor. Para-virtualization does not work with the KVM hypervisor. This procedure is for Red Hat Enterprise Linux 5.4 or newer.

8.1. Using virt-install

This section covers creating a para-virtualized Red Hat Enterprise Linux 6 guest on a Red Hat Enterprise Linux 5 host using the virt-install command. For instructions on virt-manager, refer to the procedure in Section 8.2, “Using virt-manager”.
This method installs Red Hat Enterprise Linux 6 from a remote server hosting the network installation tree. The installation instructions presented in this section are similar to installing from the minimal installation live CD-ROM.

Automating with virt-install

Guests can be created with the command line virt-install tool. The --vnc option shows the graphical installation. The name of the guest in the example is rhel6PV, the disk image file is rhel6PV.img and a local mirror of the Red Hat Enterprise Linux 6 installation tree is http://example.com/installation_tree/RHEL6-x86/. Replace those values with values for your system and network.
# virt-install --name rhel6PV \
--disk /var/lib/libvirt/images/rhel6PV.img,size=5 \
--vnc --paravirt --vcpus=2 --ram=1024 \
-location=http://example.com/installation_tree/RHEL6-x86/
Red Hat Enterprise Linux can be installed without a graphical interface or manual input. Use a Kickstart file to automate the installation process. This example extends the previous example with a Kickstart file, located at http://example.com/kickstart/ks.cfg, to fully automate the installation.
# virt-install --name rhel6PV \
--disk /var/lib/libvirt/images/rhel6PV.img,size=5 \
--nographics --paravirt --vcpus=2 --ram=1024 \
-location=http://example.com/installation_tree/RHEL6-x86/ \
-x "ks=http://example.com/kickstart/ks.cfg"
The graphical console opens showing the initial boot phase of the guest:
After your guest has completed its initial boot, the standard installation process for Red Hat Enterprise Linux 6 starts. For most systems the default answers are acceptable.
Refer to the Red Hat Enterprise Linux 6 Installation Guide for more information on installing Red Hat Enterprise Linux 6.

8.2. Using virt-manager

Procedure 8.1. Creating a para-virtualized Red Hat Enterprise Linux 6 guest with virt-manager
  1. Open virt-manager

    Start virt-manager. Launch the Virtual Machine Manager application from the Applications menu and System Tools submenu. Alternatively, run the virt-manager command as root.
  2. Select the hypervisor

    Select the hypervisor. Note that presently the KVM hypervisor is named qemu.
    Connect to a hypervisor if you have not already done so. Open the File menu and select the Add Connection... option. Refer to Section 31.5, “Adding a remote connection”.
    Once a hypervisor connection is selected the New button becomes available. Press the New button.
  3. Start the new virtual machine wizard

    Pressing the New button starts the virtual machine creation wizard.
    Press Forward to continue.
  4. Name the virtual machine

    Provide a name for your virtualized guest. The following punctuation and whitespace characters are permitted for '_', '.' and '-' characters.
    Press Forward to continue.
  5. Choose a virtualization method

    Select Xen para-virtualized as the virtualization method.
    Press Forward to continue.
  6. Select the installation method

    Red Hat Enterprise Linux can be installed using one of the following methods:
    • local install media, either an ISO image or physical optical media.
    • Select Network install tree if you have the installation tree for Red Hat Enterprise Linux hosted somewhere on your network via HTTP, FTP or NFS.
    • PXE can be used if you have a PXE server configured for booting Red Hat Enterprise Linux installation media. Configuring a sever to PXE boot a Red Hat Enterprise Linux installation is not covered by this guide. However, most of the installation steps are the same after the media boots.
    Set OS Type to Linux and OS Variant to Red Hat Enterprise Linux 5 as shown in the screenshot.
    Press Forward to continue.
  7. Locate installation media

    Select ISO image location or CD-ROM or DVD device. This example uses an ISO file image of the Red Hat Enterprise Linux installation DVD.
    1. Press the Browse button.
    2. Search to the location of the ISO file and select the ISO image. Press Open to confirm your selection.
    3. The file is selected and ready to install.
      Press Forward to continue.

    Image files and SELinux

    For ISO image files and guest storage images it is recommended to use the /var/lib/libvirt/images/ directory. Any other location may require additional configuration for SELinux, refer to Section 16.2, “SELinux and virtualization” for details.
  8. Storage setup

    Assign a physical storage device (Block device) or a file-based image (File). File-based images should be stored in the /var/lib/libvirt/images/ directory to satisfy default SELinux permissions. Assign sufficient space for your virtualized guest and any applications the guest requires.
    Press Forward to continue.

    Migration

    Live and offline migrations require guests to be installed on shared network storage. For information on setting up shared storage for guests refer to Part V, “Virtualization storage topics”.
  9. Network setup

    Select either Virtual network or Shared physical device.
    The virtual network option uses Network Address Translation (NAT) to share the default network device with the virtualized guest. Use the virtual network option for wireless networks.
    The shared physical device option uses a network bond to give the virtualized guest full access to a network device.
    Press Forward to continue.
  10. Memory and CPU allocation

    The Memory and CPU Allocation window displays. Choose appropriate values for the virtualized CPUs and RAM allocation. These values affect the host's and guest's performance.
    Virtualized guests require sufficient physical memory (RAM) to run efficiently and effectively. Choose a memory value which suits your guest operating system and application requirements. Remember, guests use physical RAM. Running too many guests or leaving insufficient memory for the host system results in significant usage of virtual memory and swapping. Virtual memory is significantly slower which causes degraded system performance and responsiveness. Ensure you allocate sufficient memory for all guests and the host to operate effectively.
    Assign sufficient virtual CPUs for the virtualized guest. If the guest runs a multithreaded application, assign the number of virtualized CPUs the guest will require to run efficiently. Do not assign more virtual CPUs than there are physical processors (or hyper-threads) available on the host system. It is possible to over allocate virtual processors, however, over allocating has a significant, negative effect on guest and host performance due to processor context switching overheads.
    Press Forward to continue.
  11. Verify and start guest installation

    Verify the configuration.
    Press Finish to start the guest installation procedure.
  12. Installing Red Hat Enterprise Linux

    Complete the Red Hat Enterprise Linux installation sequence. The installation sequence is covered by the Red Hat Enterprise Linux 6 Installation Guide. Refer to Red Hat Documentation for the Red Hat Enterprise Linux 6 Installation Guide.

Chapter 9. Installing a fully-virtualized Windows guest

Red Hat Enterprise Linux 6 supports the installation of any Microsoft Windows operating system as a fully virtualized guest. This chapter describes how to create a fully virtualized guest using the command-line (virt-install), launch the operating system's installer inside the guest, and access the installer through virt-viewer.
To install a Windows operating system on the guest, use the virt-viewer tool. This tool allows you to display the graphical console of a virtual machine (via the VNC protocol). In doing so, virt-viewer allows you to install a fully virtualized guest's operating system through that operating system's installer (e.g. the Windows XP installer).
Installing a Windows operating system involves two major steps:
  1. Creating the guest (using either virt-install or virt-manager)
  2. Installing the Windows operating system on the guest (through virt-viewer)
Note that this chapter does not describe how to install a Windows operating system on a fully-virtualized guest. Rather, it only covers how to create the guest and launch the installer within the guest. For information on how to install a Windows operating system, refer to the relevant Microsoft installation documentation.

9.1. Using virt-install to create a guest

The virt-install command allows you to create a fully-virtualized guest from a terminal, i.e. without a GUI. If you prefer to use a GUI instead, refer to Section 6.3, “Creating guests with virt-manager” for instructions on how to use virt-manager.

Important

Before creating the guest, consider first if the guest needs to use KVM Windows para-virtualized drivers. If it does, keep in mind that you can do so during or after installing the Windows operating system on the guest. For more information about para-virtualized drivers, refer to Chapter 11, KVM Para-virtualized Drivers.
For instructions on how to install KVM para-virtualized drivers, refer to Section 11.2, “Installing the KVM Windows para-virtualized drivers”.
It is possible to create a fully-virtualized guest with only a single command. To do so, simply run the following program (replace the values accordingly):
# virt-install \
   --name=guest-name  \
   --network network=default \
   --disk path=path-to-disk \
   --disk size=disk-size \
   --cdrom=path-to-install-disk \
   --vnc --ram=1024
The path-to-disk must be a device (e.g. /dev/sda3) or image file (/var/lib/libvirt/images/name.img). It must also have enough free space to support the disk-size.

Important

All image files should be stored in /var/lib/libvirt/images/. Other directory locations for file-based images are prohibited by SELinux. If you run SELinux in enforcing mode, refer to Section 16.2, “SELinux and virtualization” for more information on installing guests.
You can also run virt-install interactively. To do so, use the --prompt command, as in:
# virt-install --prompt
Once the fully-virtualized guest is created, virt-viewer will launch the guest and run the operating system's installer. Refer to to the relevant Microsoft installation documentation for instructions on how to install the operating system.

Important

If you are installing Windows 2003, you will need to select a different computer type before installing the operating system. As soon as virt-viewer launches, press F5 and refer to Section 9.2, “Installing Windows 2003” for further instructions before proceeding.

9.2. Installing Windows 2003

Windows 2003 requires a specific computer type in order to install properly on a fully-virtualized guest. This needs to be specified at the beginning of the installation process.
As soon as virt-viewer launches and boots the installer, press F5. If you do not press F5 at the right time you will need to restart the installation. Pressing F5 allows you to select a different HAL or Computer Type.
Selecting a different HAL
Figure 9.1. Selecting a different HAL

Choose Standard PC as the Computer Type. Then, press Enter to continue with the installation process.

Part III. Configuration

Chapter 10. Network Configuration

This page provides an introduction to the common networking configurations used by libvirt based applications. For additional information consult the libvirt network architecture documentation: http://libvirt.org/intro.html.
Red Hat Enterprise Linux 6 supports the following networking setups for virtualization:
  • virtual networks using Network Address Translation (NAT)
  • directly allocated physical devices using PCI passthrough or SR-IOV.
  • bridged networks
You must enable NAT, network bridging or directly share a physical device to allow external hosts access to network services on virtualized guests.

10.1. Network Address Translation (NAT) with libvirt

One of the most common methods for sharing network connections is to use Network Address Translation (NAT) forwarding (also know as virtual networks).
Host configuration
Every standard libvirt installation provides NAT based connectivity to virtual machines out of the box. This is the so called 'default virtual network'. Verify that it is available with the virsh net-list --all command.
# virsh net-list --all
Name                 State      Autostart 
-----------------------------------------
default              active     yes
If it is missing, the example XML configuration file can be reloaded and activated:
# virsh net-define /usr/share/libvirt/networks/default.xml
The default network is defined from /usr/share/libvirt/networks/default.xml
Mark the default network to automatically start:
# virsh net-autostart default
Network default marked as autostarted
Start the default network:
# virsh net-start default
Network default started
Once the libvirt default network is running, you will see an isolated bridge device. This device does not have any physical interfaces added. The new device uses NAT and IP forwarding to connect to outside world. Do not add new interfaces.
# brctl show
bridge name     bridge id               STP enabled     interfaces
virbr0          8000.000000000000       yes
libvirt adds iptables rules which allow traffic to and from guests attached to the virbr0 device in the INPUT, FORWARD, OUTPUT and POSTROUTING chains. libvirt then attempts to enable the ip_forward parameter. Some other applications may disable ip_forward, so the best option is to add the following to /etc/sysctl.conf.
 net.ipv4.ip_forward = 1
Guest configuration
Once the host configuration is complete, a guest can be connected to the virtual network based on its name. To connect a guest to the 'default' virtual network, the following could be used in the XML configuration file (such as /etc/libvirtd/qemu/myguest.xml) for the guest:
<interface type='network'>
   <source network='default'/>
</interface>

Note

Defining a MAC address is optional. A MAC address is automatically generated if omitted. Manually setting the MAC address may be useful to maintain consistency or easy reference throughout your environment, or to avoid the very small chance of a conflict.
<interface type='network'>
  <source network='default'/>
  <mac address='00:16:3e:1a:b3:4a'/>
</interface>

10.2. Bridged networking with libvirt

Bridged networking (also known as physical device sharing) is used for dedicating a physical device to a virtual machine. Bridging is often used for more advanced setups and on servers with multiple network interfaces.
Disable NetworkManager
NetworkManager does not support bridging. NetworkManager must be disabled to use networking with the network scripts (located in the /etc/sysconfig/network-scripts/ directory).
# chkconfig NetworkManager off
# chkconfig network on
# service NetworkManager stop
# service network start

Note

Instead of turning off NetworkManager, add "NM_CONTROLLED=no" to the ifcfg-* scripts used in the examples.
Creating the bridge
Create or edit the following two network configuration files. These steps can be repeated (with different names) for additional network bridges.
  1. Change to the network scripts directory

    Change to the /etc/sysconfig/network-scripts directory:
    # cd /etc/sysconfig/network-scripts
    
  2. Modify a network interface to make a bridge

    Edit the network script for the network device you are adding to the bridge. In this example, /etc/sysconfig/network-scripts/ifcfg-eth0 is used. This file defines eth0, the physical network interface which is set as part of a bridge:
    DEVICE=eth0
    # change the hardware address to match the hardware address your NIC uses
    HWADDR=00:16:76:D6:C9:45
    ONBOOT=yes
    BRIDGE=br0
    

    Tip

    You can configure the device's Maximum Transfer Unit (MTU) by appending an MTU variable to the end of the configuration file.
    MTU=9000
    
  3. Create the bridge script

    Create a new network script in the /etc/sysconfig/network-scripts directory called ifcfg-br0 or similar. The br0 is the name of the bridge, this can be anything as long as the name of the file is the same as the DEVICE parameter, and that it matches the bridge name used in step 2.
    DEVICE=br0
    TYPE=Bridge
    BOOTPROTO=dhcp
    ONBOOT=yes
    DELAY=0
    

    Warning

    The line, TYPE=Bridge, is case-sensitive. It must have uppercase 'B' and lower case 'ridge'.
  4. Restart the network

    After configuring, restart networking or reboot.
    # service network restart
    
  5. Configure iptables

    Configure iptables to allow all traffic to be forwarded across the bridge.
    # iptables -I FORWARD -m physdev --physdev-is-bridged -j ACCEPT
    # service iptables save
    # service iptables restart
    

    Disable iptables on bridges

    Alternatively, prevent bridged traffic from being processed by iptables rules. In /etc/sysctl.conf append the following lines:
    net.bridge.bridge-nf-call-ip6tables = 0
    net.bridge.bridge-nf-call-iptables = 0
    net.bridge.bridge-nf-call-arptables = 0
    
    Reload the kernel parameters configured with sysctl.
    # sysctl -p /etc/sysctl.conf
    
  6. Restart the libvirt service

    Restart the libvirt service with the service command.
    # service libvirtd reload
    
  7. Verify the bridge

    Verify the new bridge is available with the bridge control command (brctl).
    # brctl show
    bridge name     bridge id               STP enabled     interfaces
    virbr0          8000.000000000000       yes
    br0             8000.000e0cb30550       no              eth0
    
A "Shared physical device" is now available through virt-manager and libvirt, which guests can be attached and have full network access.
Note, the bridge is completely independent of the virbr0 bridge. Do not attempt to attach a physical device to virbr0. The virbr0 bridge is only for Network Address Translation (NAT) connectivity.

Chapter 11. KVM Para-virtualized Drivers

Para-virtualized drivers are available for virtualized Windows guests running on KVM hosts. These para-virtualized drivers are included in the virtio package. The virtio package supports block (storage) devices and network interface controllers.
Para-virtualized drivers enhance the performance of fully virtualized guests. With the para-virtualized drivers guest I/O latency decreases and throughput increases to near bare-metal levels. It is recommended to use the para-virtualized drivers for fully virtualized guests running I/O heavy tasks and applications.
The KVM para-virtualized drivers are automatically loaded and installed on the following:
  • Red Hat Enterprise Linux 3.9 and newer
  • Red Hat Enterprise Linux 4.8 and newer
  • Red Hat Enterprise Linux 5.3 and newer
  • Red Hat Enterprise Linux 6 and newer
  • Some versions of Linux based on the 2.6.27 kernel or newer kernel versions.
Versions of Red Hat Enterprise Linux in the list above detect and install the drivers, additional installation steps are not required.

Note

PCI devices are limited by the virtualized system architecture. Out of the 32 available PCI devices for a guest, 4 are not removable. This means there are up to 28 free PCI slots available for additional devices per guest. Each PCI device in a guest can have up to 8 functions.
The following Microsoft Windows versions are expected to function normally using KVM para-virtualized drivers:
  • Windows XP (32-bit only)
  • Windows Server 2003 (32-bit and 64-bit versions)
  • Windows Server 2008 (32-bit and 64-bit versions)
  • Windows 7 (32-bit and 64-bit versions)

11.1. Using the para-virtualized drivers with Red Hat Enterprise Linux 3.9 guests

Para-virtualized drivers for Red Hat Enterprise Linux 3.9 consist of five kernel modules: virtio, virtio_blk, virtio_net, virtio_pci and virtio_ring. All five modules must be loaded to use both the para-virtualized block and network devices drivers.

Note

To use the network device driver only, load the virtio, virtio_net and virtio_pci modules. To use the block device driver only, load the virtio, virtio_ring, virtio_blk and virtio_pci modules.

Modified initrd files

The virtio package modifies the initrd RAM disk file in the /boot directory. The original initrd file is saved to /boot/initrd- kernel-version .img.virtio.orig. The original initrd file is replaced with a new initrd RAM disk containing the virtio driver modules. The initrd RAM disk is modified to allow the guest to boot from a storage device using the para-virtualized drivers. To use a different initrd file, you must ensure that drivers are loaded with the sysinit script (Loading the para-virtualized drivers with the sysinit script) or when creating new initrd RAM disk (Adding the para-virtualized drivers to the initrd RAM disk).
Loading the para-virtualized drivers with the sysinit script
This procedure covers loading the para-virtualized driver modules during the boot sequence on a Red Hat Enterprise Linux 3.9 or newer guest with the sysinit script. Note that the guest cannot use the para-virtualized drivers for the default boot disk if the modules are loaded with the sysinit script.
The drivers must be loaded in the following order:
  1. virtio
  2. virtio_ring
  3. virtio_blk
  4. virtio_net
  5. virtio_pci
Only order of virtio_net and virtio_blk can be change. If the drivers are loaded in a different order, drivers will not work.
Configure the modules to . Locate the following section of the /etc/rc.d/rc.sysinit file.
if [ -f /etc/rc.modules ]; then
        /etc/rc.modules
fi
Append the following lines after that section:
if [ -f /etc/rc.modules ]; then
        /etc/rc.modules
fi

modprobe virtio
modprobe virtio_ring # Comment this out if you do not need block driver
modprobe virtio_blk  # Comment this out if you do not need block driver
modprobe virtio_net  # Comment this out if you do not need net driver
modprobe virtio_pci
Reboot the guest to load the kernel modules.
Adding the para-virtualized drivers to the initrd RAM disk
This procedure covers loading the para-virtualized driver modules with the kernel on a Red Hat Enterprise Linux 3.9 or newer guest by including the modules in the initrd RAM disk. The mkinitrd tool configures the initrd RAM disk to load the the modules. Specify the additional modules with the --with parameter for the mkinitrd command. Append following set of parameters, in the exact order, when using the mkinitrd command to create a custom initrd RAM disk:
--with virtio --with virtio_ring --with virtio_blk --with virtio_net --with virtio_pci
AMD64 and Intel 64 issues
Use the x86_64 version of the virtio package for AMD64 systems.
Use the ia32e version of the virtio package for Intel 64 systems. Using the x86_64 version of the virtio may cause a 'Unresolved symbol' error during the boot sequence on Intel 64 systems.
Network performance issues
If you experience low performance with the para-virtualized network drivers, verify the setting for the GSO and TSO features on the host system. The para-virtualized network drivers require that the GSO and TSO options are disabled for optimal performance.
Verify the status of the GSO and TSO settings, use the command on the host (replacing interface with the network interface used by the guest):
# ethtool -k interface
Disable the GSO and TSO options with the following commands on the host:
# ethtool -K interface gso off
# ethtool -K interface tso off
Para-virtualized driver swap partition issue
After activating the para-virtualized block device driver the swap partition may not be available. This issue is may be caused by a change in disk device name. To fix this issue, open the /etc/fstab file and locate the lines containing swap partitions, for example:
/dev/hda3		swap	swap	defaults	0 0
The para-virtualized drivers use the /dev/vd* naming convention, not the /dev/hd* naming convention. To resolve this issue modify the incorrect swap entries in the /etc/fstab file to use the /dev/vd* convention, for the example above:
			/dev/vda3		swap	swap	defaults	0 0
Save the changes and reboot the virtualized guest. The guest should now correctly have swap partitions.

11.2. Installing the KVM Windows para-virtualized drivers

This section covers the installation process for the KVM Windows para-virtualized drivers. The KVM para-virtualized drivers can be loaded during the Windows installation or installed after the guest is installed.
You can install the para-virtualized drivers on your guest by one of the following methods:
  • hosting the installation files on a network accessible to the guest,
  • using a virtualized CD-ROM device of the driver installation disk .iso file, or
  • using a virtualized floppy device to install the drivers during boot time (for Windows guests).
This guide describes installation from the para-virtualized installer disk as a virtualized CD-ROM device.
  1. Download the drivers

    The virtio-win package contains the para-virtualized block and network drivers for all supported Windows guests.
    Download the virtio-win package with the yum command.
    # yum install virtio-win
    
    The drivers are also from Microsoft (windowsservercatalog.com). Note that the Red Hat Enterprise Virtualization Hypervisor and Red Hat Enterprise Linux are created on the same code base so the drivers for the same version (for example, Red Hat Enterprise Virtualization Hypervisor 2.2 and Red Hat Enterprise Linux 5.5) are supported for both environments.
    The virtio-win package installs a CD-ROM image, virtio-win.iso, in the /usr/share/virtio-win/ directory.
  2. Install the para-virtualized drivers

    It is recommended to install the drivers on the guest before attaching or modifying a device to use the para-virtualized drivers.
    For block devices storing root file systems or other block devices required for booting the guest, the drivers must be installed before the device is modified. If the drivers are not installed on the guest and the driver is set to the virtio driver the guest will not boot.

11.2.1. Installing the drivers on an installed Windows guest

This procedure covers installing the para-virtualized drivers with a virtualized CD-ROM after Windows is installed.
Follow Procedure 11.1, “Installing from the driver CD-ROM image with virt-manager” to add a CD-ROM image with virt-manager and then install the drivers.
Procedure 11.1. Installing from the driver CD-ROM image with virt-manager
  1. Open virt-manager and the guest

    Open virt-manager, select your virtualized guest from the list by double clicking the guest name.
  2. Open the hardware window

    Click the blue Information button at the top to view guest details. Then click the Add Hardware button at the bottom of the window.
  3. Select the device type

    This opens a wizard for adding the new device. Select Storage from the dropdown menu.
    Click the Forward button to proceed.
  4. Select the ISO file

    Select Select managed or other existing storage and set the file location of the para-virtualized drivers .iso image file. The default location for the latest version of the drivers is /usr/share/virtio-win/virtio-win.iso.
    Change the Device type to IDE cdrom and click the Forward button to proceed.
  5. Finish adding virtual hardware

    Press the Finish button to complete the wizard.
  6. Reboot

    Reboot or start the guest to begin using the driver disc. Virtualized IDE devices require a restart to for the guest to recognize the new device.
Once the CD-ROM with the drivers is attached and the guest has started, proceed with Procedure 11.2, “Windows installation”.
Procedure 11.2. Windows installation
  1. Open My Computer

    On the Windows guest, open My Computer and select the CD-ROM drive.
  2. Select the correct installation files

    There are four files available on the disc. Select the drivers you require for your guest's architecture:
    • the para-virtualized block device driver (RHEV-Block.msi for 32-bit guests or RHEV-Block64.msi for 64-bit guests),
    • the para-virtualized network device driver (RHEV-Network.msi for 32-bit guests or RHEV-Block64.msi for 64-bit guests),
    • or both the block and network device drivers.
    Double click the installation files to install the drivers.
  3. Install the block device driver

    1. Start the block device driver installation

      Double click RHEV-Block.msi or RHEV-Block64.msi.
      Press Install to continue.
    2. Confirm the exception

      Windows may prompt for a security exception.
      Press Yes if it is correct.
    3. Finish

      Press Finish to complete the installation.
  4. Install the network device driver

    1. Start the network device driver installation

      Double click RHEV-Network.msi or RHEV-Network64.msi.
      Press Next to continue.
    2. Performance setting

      This screen configures advanced TCP settings for the network driver. TCP timestamps and TCP window scaling can be enabled or disabled. The default is, 1, for window scaling to be enabled.
      TCP window scaling is covered by IETF RFC 1323. The RFC defines a method of increasing the receive window size to a size greater than the default maximum of 65,535 bytes up to a new maximum of 1 gigabyte (1,073,741,824 bytes). TCP window scaling allows networks to transfer at closer to theoretical network bandwidth limits. Larger receive windows may not be supported by some networking hardware or operating systems.
      TCP timestamps are also defined by IETF RFC 1323. TCP timestamps are used to better calculate Return Travel Time estimates by embedding timing information is embedded in packets. TCP timestamps help the system to adapt to changing traffic levels and avoid congestion issues on busy networks.
      ValueAction
      0Disable TCP timestamps and window scaling.
      1Enable TCP window scaling.
      2Enable TCP timestamps.
      3Enable TCP timestamps and window scaling.
      Press Next to continue.
    3. Confirm the exception

      Windows may prompt for a security exception.
      Press Yes if it is correct.
    4. Finish

      Press Finish to complete the installation.
  5. Reboot

    Reboot the guest to complete the driver installation.
Change an existing device to use the para-virtualized drivers (Section 11.3, “Using KVM para-virtualized drivers for existing devices”) or install a new device using the para-virtualized drivers (Section 11.4, “Using KVM para-virtualized drivers for new devices”).

11.2.2. Installing drivers during the Windows installation

This procedure covers installing the para-virtualized drivers during a Windows installation.
This method allows a Windows guest to use the para-virtualized (virtio) drivers for the default storage device.
  1. Install the virtio-win package:
    # yum install virtio-win
    

    Creating guests

    Create the guest, as normal, without starting the guest. Follow one of the procedures below.
  2. Creating the guest with virsh

    This method attaches the para-virtualized driver floppy disk to a Windows guest before the installation.
    If the guest is created from an XML definition file with virsh use the virsh define command not the virsh create command.
    1. Create, but do not start, the guest. Refer to Chapter 30, Managing guests with virsh for details on creating guests with the virsh command.
    2. Add the driver disk as a virtualized floppy disk with the virsh command. This example can be copied and used if there are no other virtualized floppy devices attached to the virtualized guest.
      # virsh attach-disk guest1 /usr/share/virtio-win/virtio-drivers.vfd fda --type floppy
  3. Creating the guest with virt-manager

    1. At the final step of the virt-manager guest creation wizard, check the Customize configuration before install checkbox.
      Press the Finish button to continue.
    2. Add the new device

      Select Storage from the Hardware type list. Click Forward to continue.
    3. Select the driver disk

      Select Select managed or existing storage.
      Set the location to /usr/share/virtio-win/virtio-drivers.vfd.
      Change Device type to Floppy disk.
      Press the Forward button to continue.
    4. Confirm the new device

      Click the Finish button to confirm the device setup and add the device to the guest.
      Press the green tick button to add the new device.
  4. Creating the guest with virt-install

    Append the following parameter exactly as listed below to add the driver disk to the installation with the virt-install command :
    --disk path=/usr/share/virtio-win/virtio-drivers.vfd,device=floppy
  5. During the installation, additional steps are required to install drivers, depending on the type of Windows guest.
    1. Windows Server 2003 and Windows XP

      Before the installation blue screen repeatedly press F6 for third party drivers.
      Press S to install additional
      Press Enter to continue the installation.
    2. Windows Server 2008

      When the installer prompts you for the driver, click on Load Driver, point the installer to Drive A: and pick the driver that suits your guest operating system and architecture.

11.3. Using KVM para-virtualized drivers for existing devices

You can modify an existing hard disk device attached to the guest to use the virtio driver instead of the virtualized IDE driver. This example edits libvirt configuration files. Alternatively, virt-manager, virsh attach-disk or virsh attach-interface can add a new device using the para-virtualized drivers Section 11.4, “Using KVM para-virtualized drivers for new devices”. Note that the guest does not need to be shut down to perform these steps, however the change will not be applied until the guest is completely shut down and rebooted.
  1. Run the virsh edit <guestname> command to edit the XML configuration file for your device. For example, virsh edit guest1. The configuration files are located in /etc/libvirt/qemu.
  2. Below is a file-based block device using the virtualized IDE driver. This is a typical entry for a virtualized guest not using the para-virtualized drivers.
    <disk type='file' device='disk'>
       <source file='/var/lib/libvirt/images/disk1.img'/>
       <target dev='hda' bus='ide'/>
    </disk>
    
  3. Change the entry to use the para-virtualized device by modifying the bus= entry to virtio. Note that if the disk was previously IDE it will have a target similar to hda, hdb, or hdc and so on. When changing to bus=virtio the target needs to be changed to vda, vdb, or vdc accordingly.
    <disk type='file' device='disk'>
       <source file='/var/lib/libvirt/images/disk1.img'/>
       <target dev='vda' bus='virtio'/>
    </disk>
    
  4. Remove the address tag inside the disk tags. This must be done for this procedure to work. Libvirt will regenerate the address tag appropriately the next time the guest is started.
Please refer to the libvirt wiki: http://wiki.libvirt.org/page/Virtio for more details on using Virtio.

11.4. Using KVM para-virtualized drivers for new devices

This procedure covers creating new devices using the KVM para-virtualized drivers with virt-manager.
Alternatively, the virsh attach-disk or virsh attach-interface commands can be used to attach devices using the para-virtualized drivers.

Install the drivers first

Ensure the drivers have been installed on the Windows guest before proceeding to install new devices. If the drivers are unavailable the device will not be recognized and will not work.
Procedure 11.3. Starting the new device wizard
  1. Open the virtualized guest by double clicking on the name of the guest in virt-manager.
  2. Open the Information tab by pressing the i information button.
    The information tab button
    Figure 11.1. The information tab button

  3. In the information tab, press the Add Hardware button.
  4. In the Adding Virtual Hardware tab select Storage or Network for the type of device. The storage and network device wizards are covered in procedures Procedure 11.4, “Adding a storage device using the para-virtualized storage driver” and Procedure 11.5, “Adding a network device using the para-virtualized network driver”
Procedure 11.4. Adding a storage device using the para-virtualized storage driver
  1. Select hardware type

    Select Storage as the Hardware type.
    Press Forward to continue.
  2. Select the storage device and driver

    Create a new disk image or select a storage pool volume.
    Set the Device type to Virtio Disk to use the para-virtualized drivers.
    Press Forward to continue.
  3. Finish the procedure

    Confirm the details for the new device are correct.
    Press Finish to complete the procedure.
Procedure 11.5. Adding a network device using the para-virtualized network driver
  1. Select hardware type

    Select Network as the Hardware type.
    Press Forward to continue.
  2. Select the network device and driver

    Select the network device from the Host device list.
    Create a custom MAC address or use the one provided.
    Set the Device model to virtio to use the para-virtualized drivers.
    Press Forward to continue.
  3. Finish the procedure

    Confirm the details for the new device are correct.
    Press Finish to complete the procedure.
Once all new devices are added, reboot the guest. Windows guests may may not recognise the devices until the guest is rebooted.

Chapter 12. PCI passthrough

This chapter covers using PCI passthrough with KVM.
Certain hardware platforms allow virtualized guests to directly access various hardware devices and components. This process in virtualization is known as passthrough. Passthrough is known as device assignment in some of the KVM documentation and the KVM code.
The KVM hypervisor supports attaching PCI devices on the host system to virtualized guests. PCI passthrough allows guests to have exclusive access to PCI devices for a range of tasks. PCI passthrough allows PCI devices to appear and behave as if they were physically attached to the guest operating system. PCI passthrough can improve the I/O performance of devices attached to virtualized guests.
Almost all PCI and PCI Express devices that support passthrough, except for graphics cards, can be directly attached to virtualized guests with PCI passthrough.
PCI passthrough is only available on hardware platforms supporting either Intel VT-d or AMD IOMMU. These Intel VT-d or AMD IOMMU extensions must be enabled in BIOS for PCI passthrough to function.
Red Hat Enterprise Linux 6.0 and newer supports hot plugging PCI passthrough devices into virtualized guests.
Out of the 32 available PCI devices for a guest 4 are not removable. This means there are only 28 PCI slots available for additional devices per guest. Every para-virtualized network or block device uses one slot. Each guest can use up to 28 additional devices made up of any combination of para-virtualized network, para-virtualized disk devices, or other PCI devices using VT-d.
Procedure 12.1. Preparing an Intel system for PCI passthrough
  1. Enable the Intel VT-d extensions

    The Intel VT-d extensions provides hardware support for directly assigning a physical devices to guest.
    The VT-d extensions are required for PCI passthrough with Red Hat Enterprise Linux. The extensions must be enabled in the BIOS. Some system manufacturers disable these extensions by default.
    These extensions are often called various terms in BIOS which differ from manufacturer to manufacturer. Consult your system manufacturer's documentation.
  2. Activate Intel VT-d in the kernel

    Activate Intel VT-d in the kernel by appending the intel_iommu=on parameter to the kernel line of the kernel line in the /boot/grub/grub.conf file.
    The example below is a modified grub.conf file with Intel VT-d activated.
    default=0
    timeout=5
    splashimage=(hd0,0)/grub/splash.xpm.gz
    hiddenmenu
    title Red Hat Enterprise Linux Server (2.6.32-36.x86-645)
            root (hd0,0)
            kernel /vmlinuz-2.6.32-36.x86-64 ro root=/dev/VolGroup00/LogVol00 rhgb quiet intel_iommu=on
            initrd /initrd-2.6.32-36.x86-64.img
  3. Ready to use

    Reboot the system to enable the changes. Your system is now PCI passthrough capable.
Procedure 12.2. Preparing an AMD system for PCI passthrough
  • Enable AMD IOMMU extensions

    The AMD IOMMU extensions are required for PCI passthrough with Red Hat Enterprise Linux. The extensions must be enabled in the BIOS. Some system manufacturers disable these extensions by default.
AMD systems only require that the IOMMU is enabled in the BIOS. The system is ready for PCI passthrough once the IOMMU is enabled.

12.1. Adding a PCI device with virsh

These steps cover adding a PCI device to a virtualized guest on a KVM hypervisor using hardware-assisted PCI passthrough.
This example uses a USB controller device with the PCI identifier code, pci_8086_3a6c, and a fully virtualized guest named win2k3.
  1. Identify the device

    Identify the PCI device designated for passthrough to the guest. The virsh nodedev-list command lists all devices attached to the system. The --tree option is useful for identifying devices attached to the PCI device (for example, disk controllers and USB controllers).
    # virsh nodedev-list --tree
    For a list of only PCI devices, run the following command:
    # virsh nodedev-list | grep pci
    In the output from this command, each PCI device is identified by a string, as shown in the following example output:
    pci_0000_00_00_0
    pci_0000_00_02_0
    pci_0000_00_02_1
    pci_0000_00_03_0
    pci_0000_00_03_2
    pci_0000_00_03_3
    pci_0000_00_19_0
    pci_0000_00_1a_0
    pci_0000_00_1a_1
    pci_0000_00_1a_2
    pci_0000_00_1a_7
    pci_0000_00_1b_0
    pci_0000_00_1c_0
    

    Tip: determining the PCI device

    Comparing lspci output to lspci -n (which turns off name resolution) output can assist in deriving which device has which device identifier code.
    Record the PCI device number; the number is needed in other steps.
  2. Information on the domain, bus and function are available from output of the virsh nodedev-dumpxml command:
    # virsh nodedev-dumpxml pci_8086_3a6c
    <device>
      <name>pci_8086_3a6c</name>
      <parent>computer</parent>
      <capability type='pci'>
        <domain>0</domain>
        <bus>0</bus>
        <slot>26</slot>
        <function>7</function>
        <id='0x3a6c'>82801JD/DO (ICH10 Family) USB2 EHCI Controller #2</product>
        <vendor id='0x8086'>Intel Corporation</vendor>
      </capability>
    </device>
  3. Detach the device from the system. Attached devices cannot be used and may cause various errors if connected to a guest without detaching first.
    # virsh nodedev-dettach pci_8086_3a6c 
    Device pci_8086_3a6c dettached
  4. Convert slot and function values to hexadecimal values (from decimal) to get the PCI bus addresses. Append "0x" to the beginning of the output to tell the computer that the value is a hexadecimal number.
    For example, if bus = 0, slot = 26 and function = 7 run the following:
    $ printf %x 0
    0
    $ printf %x 26
    1a
    $ printf %x 7
    7
    The values to use:
    bus='0x00'
    slot='0x1a'
    function='0x7'
  5. Run virsh edit (or virsh attach device) and added a device entry in the <devices> section to attach the PCI device to the guest.
    # virsh edit win2k3
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <source>
          <address domain='0x0000' bus='0x00' slot='0x1a' function='0x7'/>
      </source>
    </hostdev>
  6. Once the guest system is configured to use the PCI address, the host system must be configured to stop using the device. The ehci driver is loaded by default for the USB PCI controller.
    $ readlink /sys/bus/pci/devices/0000\:00\:1a.7/driver
    ../../../bus/pci/drivers/ehci_hcd
  7. Detach the device:
    $ virsh nodedev-dettach pci_8086_3a6c
  8. Verify it is now under the control of pci_stub:
    $ readlink /sys/bus/pci/devices/0000\:00\:1d.7/driver
    ../../../bus/pci/drivers/pci-stub
  9. Set a sebool to allow the management of the PCI device from the guest:
    $ setsebool -P virt_manage_sysfs 1
  10. Start the guest system :
    # virsh start win2k3
The PCI device should now be successfully attached to the guest and accessible to the guest operating system.

12.2. Adding a PCI device with virt-manager

PCI devices can be added to guests using the graphical virt-manager tool. The following procedure adds a 2 port USB controller to a virtualized guest.
  1. Identify the device

    Identify the PCI device designated for passthrough to the guest. The virsh nodedev-list command lists all devices attached to the system. The --tree option is useful for identifying devices attached to the PCI device (for example, disk controllers and USB controllers).
    # virsh nodedev-list --tree
    For a list of only PCI devices, run the following command:
    # virsh nodedev-list | grep pci
    In the output from this command, each PCI device is identified by a string, as shown in the following example output:
    pci_0000_00_00_0
    pci_0000_00_02_0
    pci_0000_00_02_1
    pci_0000_00_03_0
    pci_0000_00_03_2
    pci_0000_00_03_3
    pci_0000_00_19_0
    pci_0000_00_1a_0
    pci_0000_00_1a_1
    pci_0000_00_1a_2
    pci_0000_00_1a_7
    pci_0000_00_1b_0
    pci_0000_00_1c_0
    

    Tip: determining the PCI device

    Comparing lspci output to lspci -n (which turns off name resolution) output can assist in deriving which device has which device identifier code.
    Record the PCI device number; the number is needed in other steps.
  2. Detach the PCI device

    Detach the device from the system.
    # virsh nodedev-dettach pci_8086_3a6c 
    Device pci_8086_3a6c dettached
  3. Open the hardware settings

    Open the virtual machine and click the Add Hardware button to add a new device to the guest.
  4. Add the new device

    Select Physical Host Device from the Hardware type list. Click Forward to continue.
  5. Select a PCI device

    Select an unused PCI device. Note that selecting PCI devices presently in use on the host causes errors. In this example a PCI to USB interface device is used.
  6. Confirm the new device

    Click the Finish button to confirm the device setup and add the device to the guest.
The setup is complete and the guest can now use the PCI device.

12.3. PCI passthrough with virt-install

To use PCI passthrough with the virt-install parameter, use the additional --host-device parameter.
  1. Identify the PCI device

    Identify the PCI device designated for passthrough to the guest. The virsh nodedev-list command lists all devices attached to the system. The --tree option is useful for identifying devices attached to the PCI device (for example, disk controllers and USB controllers).
    # virsh nodedev-list --tree
    For a list of only PCI devices, run the following command:
    # virsh nodedev-list | grep pci
    In the output from this command, each PCI device is identified by a string, as shown in the following example output:
    pci_0000_00_00_0
    pci_0000_00_02_0
    pci_0000_00_02_1
    pci_0000_00_03_0
    pci_0000_00_03_2
    pci_0000_00_03_3
    pci_0000_00_19_0
    pci_0000_00_1a_0
    pci_0000_00_1a_1
    pci_0000_00_1a_2
    pci_0000_00_1a_7
    pci_0000_00_1b_0
    pci_0000_00_1c_0
    

    Tip: determining the PCI device

    Comparing lspci output to lspci -n (which turns off name resolution) output can assist in deriving which device has which device identifier code.
  2. Add the device

    Use the PCI identifier output from the virsh nodedev command as the value for the --host-device parameter.
    # virt-install \
     -n hostdev-test -r 1024 --vcpus 2 \
     --os-variant fedora11 -v \
     -l http://download.fedoraproject.org/pub/fedora/linux/development/x86_64/os \
     -x 'console=ttyS0 vnc' --nonetworks --nographics  \
     --disk pool=default,size=8 \
     --debug --host-device=pci_8086_10bd 
  3. Complete the installation

    Complete the guest installation. The PCI device should be attached to the guest.

Chapter 13. SR-IOV

13.1. Introduction

The PCI-SIG (PCI Special Interest Group) developed the Single Root I/O Virtualization (SR-IOV) specification. The SR-IOV specification is a standard for a type of PCI passthrough which natively shares a single device to multiple guests. SR-IOV reduces hypervisor involvement by specifying virtualization compatible memory spaces, interrupts and DMA streams. SR-IOV improves device performance for virtualized guests.
How SR-IOV works
Figure 13.1. How SR-IOV works

SR-IOV enables a Single Root Function (for example, a single Ethernet port), to appear as multiple, separate, physical devices. A physical device with SR-IOV capabilities can be configured to appear in the PCI configuration space as multiple functions, each device has its own configuration space complete with Base Address Registers (BARs).
SR-IOV uses two new PCI functions:
  • Physical Functions (PFs) are full PCIe devices that include the SR-IOV capabilities. Physical Functions are discovered, managed, and configured as normal PCI devices. Physical Functions configure and manage the SR-IOV functionality by assigning Virtual Functions.
  • Virtual Functions (VFs) are simple PCIe functions that only process I/O. Each Virtual Function is derived from a Physical Function. The number of Virtual Functions a device may have is limited by the device hardware. A single Ethernet port, the Physical Device, may map to many Virtual Functions that can be shared to virtualized guests.
The hypervisor can map one or more Virtual Functions to a virtualized guest. The Virtual Function's configuration space is mapped to the configuration space presented to the virtualized guest by the hypervisor.
Each Virtual Function can only be mapped to a single guest at a time, as Virtual Functions require real hardware resources. A virtualized guest can have multiple Virtual Functions. A Virtual Function appears as a network card in the same way as a normal network card would appear to an operating system.
The SR-IOV drivers are implemented in the kernel. The core implementation is contained in the PCI subsystem, but there must also be driver support for both the Physical Function (PF) and Virtual Function (VF) devices. With an SR-IOV capable device one can allocate VFs from a PF. The VFs appear as PCI devices which are backed on the physical PCI device by resources (queues, and register sets).
Migrating guests with SR-IOV is possible with the vhost-net feature.
Advantages of SR-IOV
SR-IOV devices can share a single physical port with multiple virtualized guests.
Virtual Functions have near-native performance and provide better performance than para-virtualized drivers and emulated access. Virtual Functions provide data protection between virtualized guests on the same physical server as the data is managed and controlled by the hardware.
These features allow for increased virtualized guest density on hosts within a data center.
SR-IOV is better able to utilize the bandwidth of devices with multiple guests.

13.2. Using SR-IOV

This section covers attaching Virtual Function to a guest as an additional network device.
SR-IOV requires Intel VT-d support.
Procedure 13.1. Attach an SR-IOV network device
  1. Enable Intel VT-d in BIOS and in the kernel

    Skip this step if Intel VT-d is already enabled and working.
    Enable Intel VT-D in BIOS if it is not enabled already. Refer to Procedure 12.1, “Preparing an Intel system for PCI passthrough” for procedural help on enabling Intel VT-d in BIOS and the kernel.
  2. Verify support

    Verify if the PCI device with SR-IOV capabilities are detected. This example lists an Intel 82576 network interface card which supports SR-IOV. Use the lspci command to verify if the device was detected.
    # lspci
    03:00.0 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)
    03:00.1 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)
    
    Note that the output has been modified to remove all other devices.
  3. Start the SR-IOV kernel modules

    If the device is supported the driver kernel module should be loaded automatically by the kernel. Optional parameters can be passed to the module using the modprobe command. The Intel 82576 network interface card uses the igb driver kernel module.
    # modprobe igb [<option>=<VAL1>,<VAL2>,]
    # lsmod |grep igb
    igb    87592  0
    dca    6708    1 igb
    
  4. Activate Virtual Functions

    The max_vfs parameter of the igb module allocates the maximum number of Virtual Functions. The max_vfs parameter causes the driver to spawn, up to the value of the parameter in, Virtual Functions. For this particular card the valid range is 0 to 7.
    Remove the module to change the variable.
    # modprobe -r igb
    Restart the module with the max_vfs set to 1 or any number of Virtual Functions up to the maximum supported by your device.
    # modprobe igb max_vfs=7
    
  5. Make the Virtual Functions persistent

    The modprobe command /etc/modprobe.d/igb.conf options igb max_vfs=7
  6. Inspect the new Virtual Functions

    Using the lspci command, list the newly added Virtual Functions attached to the Intel 82576 network device.
    # lspci | grep 82576
    0b:00.0 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)
    0b:00.1 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)
    0b:10.0 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
    0b:10.1 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
    0b:10.2 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
    0b:10.3 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
    0b:10.4 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
    0b:10.5 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
    0b:10.6 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
    0b:10.7 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
    0b:11.0 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
    0b:11.1 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
    0b:11.2 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
    0b:11.3 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
    0b:11.4 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
    0b:11.5 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)
    
    The identifier for the PCI device is found with the -n parameter of the lspci command. The Physical Functions corresponds to 0b:00.0 and 0b:00.1. All the Virtual Functions have Virtual Function in the description.
  7. Verify devices exist with virsh

    The libvirt service must recognize the device before adding a device to a guest. libvirt uses a similar notation to the lspci output. All punctuation characters, ; and ., in lspci output are changed to underscores (_).
    Use the virsh nodedev-list command and the grep command to filter the Intel 82576 network device from the list of available host devices. 0b is the filter for the Intel 82576 network devices in this example. This may vary for your system and may result in additional devices.
    # virsh nodedev-list | grep 0b
    pci_0000_0b_00_0
    pci_0000_0b_00_1
    pci_0000_0b_10_0
    pci_0000_0b_10_1
    pci_0000_0b_10_2
    pci_0000_0b_10_3
    pci_0000_0b_10_4
    pci_0000_0b_10_5
    pci_0000_0b_10_6
    pci_0000_0b_11_7
    pci_0000_0b_11_1
    pci_0000_0b_11_2
    pci_0000_0b_11_3
    pci_0000_0b_11_4
    pci_0000_0b_11_5
    
    The serial numbers for the Virtual Functions and Physical Functions should be in the list.
  8. Get device details with virsh

    The pci_0000_0b_00_0 is one of the Physical Functions and pci_0000_0b_10_0 is the first corresponding Virtual Function for that Physical Function. Use the virsh nodedev-dumpxml command to get advanced output for both devices.
    <device>
        <name>pci_0000_0b_00_0</name>
        <parent>pci_0000_00_01_0</parent>
        <driver>
          <name>igb</name>
        </driver>
        <capability type='pci'>
          <domain>0</domain>
          <bus>11</bus>
          <slot>0</slot>
          <function>0</function>
          <product id='0x10c9'>Intel Corporation</product>
          <vendor id='0x8086'>82576 Gigabit Network Connection</vendor>
        </capability>
      </device>
    # virsh nodedev-dumpxml pci_0000_0b_10_0
      <device>
        <name>pci_0000_0b_10_0</name>
        <parent>pci_0000_00_01_0</parent>
        <driver>
          <name>igbvf</name>
        </driver>
        <capability type='pci'>
          <domain>0</domain>
          <bus>11</bus>
          <slot>16</slot>
          <function>0</function>
          <product id='0x10ca'>Intel Corporation</product>
          <vendor id='0x8086'>82576 Virtual Function</vendor>
        </capability>
      </device>
    
    This example adds the Virtual Function pci_0000_0b_10_0 to the guest in Step 10. Note the bus, slot and function parameters of the Virtual Function, these are required for adding the device.
  9. Detach the Virtual Functions

    Devices attached to a host cannot be attached to guests. Red Hat Enterprise Linux automatically attaches new devices to the host. Detach the Virtual Function from the host so that the Virtual Function can be used by the guest. Detaching the Physical Function causes errors, only detach the required Virtual Functions.
    # virsh nodedev-dettach pci_0000_0b_10_0
    Device pci_0000_0b_10_0 dettached
    
  10. Add the Virtual Function to the guest

    1. Shut down the guest.
    2. Use the output from the virsh nodedev-dumpxml pci_8086_10ca_0 command to calculate the values for the configuration file. Convert slot and function values to hexadecimal values (from decimal) to get the PCI bus addresses. Append "0x" to the beginning of the output to tell the computer that the value is a hexadecimal number.
      The example device has the following values: bus = 3, slot = 16 and function = 1. Use the printf utility to convert decimal values to hexadecimal values.
      $ printf %x 3
      3
      $ printf %x 16
      10
      $ printf %x 1
      1
      This example would use the following values in the configuration file:
      bus='0x03'
      slot='0x10'
      function='0x01'
    3. Open the XML configuration file with the virsh edit command. This example edits a guest named MyGuest.
      # virsh edit MyGuest
    4. The default text editor will open the libvirt configuration file for the guest. Add the new device to the devices section of the XML configuration file.
      <hostdev mode='subsystem' type='pci'>
            <source>
              <address bus='0x03' slot='0x10' function='0x01'/>
            </source>
      </hostdev>
      
    5. Save the configuration.
  11. Restart

    Restart the guest to complete the installation.
    # virsh start MyGuest
The guest should start successfully and detect a new network interface card. This new card is the Virtual Function of the SR-IOV device.

13.3. Troubleshooting SR-IOV

This section contains some issues and solutions for problems which may affect SR-IOV.
Error starting the guest
Start the configured vm , an error reported as follows:
# virsh start test
error: Failed to start domain test
error: internal error unable to start guest: char device redirected to
/dev/pts/2
get_real_device: /sys/bus/pci/devices/0000:03:10.0/config: Permission denied
init_assigned_device: Error: Couldn't get real device (03:10.0)!
Failed to initialize assigned device host=03:10.0
This error is often caused by a device which is already assigned to another guest or to the host itself.

Chapter 14. KVM guest timing management

Virtualization poses various challenges for guest time keeping. Guests using the Time Stamp Counter (TSC) as a clock source may suffer timing issues as some CPUs do not have a constant Time Stamp Counter. Guests without accurate timekeeping may have issues with some networked applications and processes as the guest will run faster or slower than the actual time and fall out of synchronization.
KVM works around this issue by providing guests with a para-virtualized clock. Alternatively, some guests may use other x86 clock sources for their timing in future versions of those operating systems.
Guests can have several problems caused by inaccurate clocks and counters:
  • Clocks can fall out of synchronization with the actual time which invalidates sessions and affects networks.
  • Guests with slower clocks may have issues migrating.
These problems exist on other virtualization platforms and timing should always be tested.

NTP

The Network Time Protocol (NTP) daemon should be running on the host and the guests. Enable the ntpd service:
# service ntpd start
Add the ntpd service to the default startup sequence:
# chkconfig ntpd on
Using the ntpd service should minimize the affects of clock skew in all cases.
Determining if your CPU has the constant Time Stamp Counter
Your CPU has a constant Time Stamp Counter if the constant_tsc flag is present. To determine if your CPU has the constant_tsc flag run the following command:
$ cat /proc/cpuinfo | grep constant_tsc
If any output is given your CPU has the constant_tsc bit. If no output is given follow the instructions below.
Configuring hosts without a constant Time Stamp Counter
Systems without constant time stamp counters require additional configuration. Power management features interfere with accurate time keeping and must be disabled for guests to accurately keep time with KVM.

Note

These instructions are for AMD revision F cpus only.
If the CPU lacks the constant_tsc bit, disable all power management features (BZ#513138). Each system has several timers it uses to keep time. The TSC is not stable on the host, which is sometimes caused by cpufreq changes, deep C state, or migration to a host with a faster TSC. Deep C sleep states can stop the TSC. To prevent the kernel using deep C states append processor.max_cstate=1 to the kernel boot options in the grub.conf file on the host:
title Red Hat Enterprise Linux (2.6.32-36.x86-64)
        root (hd0,0)
	kernel /vmlinuz-2.6.32-36.x86-64 ro root=/dev/VolGroup00/LogVol00 rhgb quiet processor.max_cstate=1
Disable cpufreq (only necessary on hosts without the constant_tsc) by editing the /etc/sysconfig/cpuspeed configuration file and change the MIN_SPEED and MAX_SPEED variables to the highest frequency available. Valid limits can be found in the /sys/devices/system/cpu/cpu*/cpufreq/scaling_available_frequencies files.
Using the para-virtualized clock with Red Hat Enterprise Linux guests
For certain Red Hat Enterprise Linux guests, additional kernel parameters are required. These parameters can be set by appending them to the end of the /kernel line in the /boot/grub/grub.conf file of the guest.
The table below lists versions of Red Hat Enterprise Linux and the parameters required for guests on systems without a constant Time Stamp Counter.
Red Hat Enterprise LinuxAdditional guest kernel parameters
6.0 AMD64/Intel 64 with the para-virtualized clockAdditional parameters are not required
6.0 AMD64/Intel 64 without the para-virtualized clocknotsc lpj=n
5.5 AMD64/Intel 64 with the para-virtualized clockAdditional parameters are not required
5.5 AMD64/Intel 64 without the para-virtualized clockdivider=10 notsc lpj=n
5.5 x86 with the para-virtualized clockAdditional parameters are not required
5.5 x86 without the para-virtualized clockdivider=10 clocksource=acpi_pm lpj=n
5.4 AMD64/Intel 64divider=10 notsc
5.4 x86divider=10 clocksource=acpi_pm
5.3 AMD64/Intel 64divider=10 notsc
5.3 x86divider=10 clocksource=acpi_pm
4.8 AMD64/Intel 64notsc divider=10
4.8 x86clock=pmtmr divider=10
3.9 AMD64/Intel 64 Additional parameters are not required
3.9 x86Additional parameters are not required
Using the Real-Time Clock with Windows Server 2003 and Windows XP guests
Windows uses the both the Real-Time Clock (RTC) and the Time Stamp Counter (TSC). For Windows guests the Real-Time Clock can be used instead of the TSC for all time sources which resolves guest timing issues.
To enable the Real-Time Clock for the PMTIMER clock source (the PMTIMER usually uses the TSC) add the following line to the Windows boot settings. Windows boot settings are stored in the boot.ini file. Add the following line to the boot.ini file:
/use pmtimer
For more information on Windows boot settings and the pmtimer option, refer to Available switch options for the Windows XP and the Windows Server 2003 Boot.ini files.
Using the Real-Time Clock with Windows Vista, Windows Server 2008 and Windows 7 guests
Windows uses the both the Real-Time Clock (RTC) and the Time Stamp Counter (TSC). For Windows guests the Real-Time Clock can be used instead of the TSC for all time sources which resolves guest timing issues.
The boot.ini file is no longer used from Windows Vista and newer. Windows Vista, Windows Server 2008 and Windows 7 use the Boot Configuration Data Editor (bcdedit.exe) to modify the Windows boot parameters.
This procedure is only required if the guest is having time keeping issues. Time keeping issues may not affect guests on all host systems.
  1. Open the Windows guest.
  2. Open the Accessories menu of the start menu. Right click on the Command Prompt application, select Run as Administrator.
  3. Confirm the security exception, if prompted.
  4. Set the boot manager to use the platform clock. This should instruct Windows to use the PM timer for the primary clock source. The system UUID ({default} in the example below) should be changed if the system UUID is different than the default boot device.
    C:\Windows\system32>bcdedit /set {default} USEPLATFORMCLOCK on
    The operation completed successfully
This fix should improve time keeping for Windows Vista, Windows Server 2008 and Windows 7 guests.

Part IV. Administration

Administering virtualized systems

These chapters contain information for administering host and virtualized guests using tools included in Red Hat Enterprise Linux 6.

Table of Contents

15. Server best practices
16. Security for virtualization
16.1. Storage security issues
16.2. SELinux and virtualization
16.3. SELinux
16.4. Virtualization firewall information
17. sVirt
17.1. Security and Virtualization
17.2. sVirt labeling
18. KVM live migration
18.1. Live migration requirements
18.2. Shared storage example: NFS for a simple migration
18.3. Live KVM migration with virsh
18.4. Migrating with virt-manager
19. Remote management of virtualized guests
19.1. Remote management with SSH
19.2. Remote management over TLS and SSL
19.3. Transport modes
20. Overcommitting with KVM
21. KSM
22. Advanced virtualization administration
22.1. Guest scheduling
22.2. Advanced memory management
22.3. Guest block I/O throttling
22.4. Guest network I/O throttling
23. Migrating to KVM from other hypervisors using virt-v2v
23.1. Preparing to convert a virtualized guest
23.2. Converting virtualized guests
23.2.1. virt-v2v
23.2.2. Converting a local Xen virtualized guest
23.2.3. Converting a remote Xen virtualized guest
23.2.4. Converting a VMware ESX virtualized guest
23.2.5. Converting a virtualized guest running Windows
23.3. Running converted virtualized guests
23.4. Configuration changes
23.4.1. Configuration changes for Linux virtualized guests
23.4.2. Configuration changes for Windows virtualized guests
24. Miscellaneous administration tasks
24.1. Automatically starting guests
24.2. Using qemu-img
24.3. Verifying virtualization extensions
24.4. Setting KVM processor affinities
24.5. Generating a new unique MAC address
24.6. Improving guest response time
24.7. Very Secure ftpd
24.8. Disable SMART disk monitoring for guests
24.9. Configuring a VNC Server
24.10. Gracefully shutting down guests
24.11. Virtual machine timer management with libvirt

Chapter 15. Server best practices

The following tasks and tips can assist you with securing and ensuring reliability of your Red Hat Enterprise Linux host.
  • Run SELinux in enforcing mode. Set SELinux to run in enforcing mode with the setenforce command.
    # setenforce 1
    
  • Remove or disable any unnecessary services such as AutoFS, NFS, FTP, HTTP, NIS, telnetd, sendmail and so on.
  • Only add the minimum number of user accounts needed for platform management on the server and remove unnecessary user accounts.
  • Avoid running any unessential applications on your host. Running applications on the host may impact virtual machine performance and can affect server stability. Any application which may crash the server will also cause all virtual machines on the server to go down.
  • Use a central location for virtual machine installations and images. Virtual machine images should be stored under /var/lib/libvirt/images/. If you are using a different directory for your virtual machine images make sure you add the directory to your SELinux policy and relabel it before starting the installation.
  • Installation sources, trees, and images should be stored in a central location, usually the location of your vsftpd server.

Chapter 16. Security for virtualization

When deploying virtualization technologies on your corporate infrastructure, you must ensure that the host cannot be compromised. The host is a Red Hat Enterprise Linux system that manages the system, devices, memory and networks as well as all virtualized guests. If the host is insecure, all guests in the system are vulnerable. There are several ways to enhance security on systems using virtualization. You or your organization should create a Deployment Plan containing the operating specifications and specifies which services are needed on your virtualized guests and host servers as well as what support is required for these services. Here are a few security issues to consider while developing a deployment plan:
  • Run only necessary services on hosts. The fewer processes and services running on the host, the higher the level of security and performance.
  • Enable SELinux on the hypervisor. Read Section 16.2, “SELinux and virtualization” for more information on using SELinux and virtualization.
  • Use a firewall to restrict traffic to the host. You can setup a firewall with default-reject rules that will help secure the host from attacks. It is also important to limit network-facing services.
  • Do not allow normal users to access the host. The host is privileged, and granting access to unprivileged accounts may compromise the level of security.

16.1. Storage security issues

Administrators of virtualized guests can change the partitions the host boots in certain circumstances. To prevent this administrators should follow these recommendations:
The host should not use disk labels to identify file systems in the fstab file, the initrd file or used by the kernel command line. If less privileged users, especially virtualized guests, have write access to whole partitions or LVM volumes.
Guests should not be given write access to whole disks or block devices (for example, /dev/sdb). Use partitions (for example, /dev/sdb1) or LVM volumes.

16.2. SELinux and virtualization

Security Enhanced Linux was developed by the NSA with assistance from the Linux community to provide stronger security for Linux. SELinux limits an attackers abilities and works to prevent many common security exploits such as buffer overflow attacks and privilege escalation. It is because of these benefits that all Red Hat Enterprise Linux systems should run with SELinux enabled and in enforcing mode.
SELinux prevents guest images from loading if SELinux is enabled and the images are not in the correct directory. SELinux requires that all guest images are stored in /var/lib/libvirt/images.
Adding LVM based storage with SELinux in enforcing mode
The following section is an example of adding a logical volume to a virtualized guest with SELinux enabled. These instructions also work for hard drive partitions.
Procedure 16.1. Creating and mounting a logical volume on a virtualized guest with SELinux enabled
  1. Create a logical volume. This example creates a 5 gigabyte logical volume named NewVolumeName on the volume group named volumegroup.
    # lvcreate -n NewVolumeName -L 5G volumegroup
  2. Format the NewVolumeName logical volume with a file system that supports extended attributes, such as ext3.
    # mke2fs -j /dev/volumegroup/NewVolumeName
  3. Create a new directory for mounting the new logical volume. This directory can be anywhere on your file system. It is advised not to put it in important system directories (/etc, /var, /sys) or in home directories (/home or /root). This example uses a directory called /virtstorage
    # mkdir /virtstorage
  4. Mount the logical volume.
    # mount /dev/volumegroup/NewVolumeName /virtstorage
  5. Set the correct SELinux type for the libvirt image folder.
    # semanage fcontext -a -t virt_image_t "/virtstorage(/.*)?"
    
    If the targeted policy is used (targeted is the default policy) the command appends a line to the /etc/selinux/targeted/contexts/files/file_contexts.local file which makes the change persistent. The appended line may resemble this:
    /virtstorage(/.*)?    system_u:object_r:virt_image_t:s0
    
  6. Run the command to change the type of the mount point (/virtstorage) and all files under it to virt_image_t (the restorecon and setfiles commands read the files in /etc/selinux/targeted/contexts/files/).
    # restorecon -R -v /virtstorage
    

Testing new attributes

Create a new file (using the touch command) on the file system.
# touch /virtstorage/newfile
Verify the file has been relabeled using the following command:
# sudo ls -Z /virtstorage
-rw-------. root root system_u:object_r:virt_image_t:s0 newfile
The output shows that the new file has the correct attribute, virt_image_t.

16.3. SELinux

This sections contains topics to consider when using SELinux with your virtualization deployment. When you deploy system changes or add devices, you must update your SELinux policy accordingly. To configure an LVM volume for a guest, you must modify the SELinux context for the respective underlying block device and volume group.
# semanage fcontext -a -t virt_image _t -f -b /dev/sda2
# restorecon /dev/sda2
KVM and SELinux
There are several SELinux Booleans which affect KVM and libvirt. These Booleans are listed below for your convenience.
KVM SELinux Booleans
SELinux BooleanDescription
allow_unconfined_qemu_transitionDefault: off. This Boolean controls whether KVM guests can be transitioned to unconfined users.
qemu_full_networkDefault: on. This Boolean controls full network access to KVM guests.
qemu_use_cifsDefault: on. This Boolean controls KVM's access to CIFS or Samba file systems.
qemu_use_commDefault: off. This Boolean controls whether KVM can access serial or parallel communications ports.
qemu_use_nfsDefault: on. This Boolean controls KVM's access to NFS file systems.

16.4. Virtualization firewall information

Various ports are used for communication between virtualized guests and management utilities.

Guest network services

Any network service on a virtualized guest must have the applicable ports open on the guest to allow external access. If a network service on a guest is firewalled it will be inaccessible. Always verify the guests network configuration first.
  • ICMP requests must be accepted. ICMP packets are used for network testing. You cannot ping guests if ICMP packets are blocked.
  • Port 22 should be open for SSH access and the initial installation.
  • Ports 80 or 443 (depending on the security settings on the RHEV Manager) are used by the vdsm-reg service to communicate information about the host.
  • Ports 5634 to 6166 are used for guest console access with the SPICE protocol.
  • Ports 49152 to 49216 are used for migrations with KVM. Migration may use any port in this range depending on the number of concurrent migrations occurring.
  • Enabling IP forwarding (net.ipv4.ip_forward = 1) is also required for shared bridges and the default bridge. Note that installing libvirt enables this variable so it will be enabled when the virtualization packages are installed unless it was manually disabled.

Chapter 17. sVirt

sVirt is a technology included in Red Hat Enterprise Linux 6 that integrates SELinux and virtualization. sVirt applies Mandatory Access Control (MAC) to improve security when using virtualized guests. The main reasons for integrating these technologies are to improve security and harden the system against bugs in the hypervisor that might be used as an attack vector aimed toward the host or to another virtualized guest.
This chapter describes how sVirt integrates with virtualization technologies in Red Hat Enterprise Linux 6.
Non-virtualized environments
In a non-virtualized environment, hosts are separated from each other physically and each host has a self-contained environment, consisting of services such as a web server, or a DNS server. These services communicate directly to their own user space, host kernel and physical host, offering their services directly to the network. The following image represents a non-virtualized environment:
Virtualized environments
In a virtualized environment, several operating systems can run on a single host kernel and physical host. The following image represents a virtualized environment:

17.1. Security and Virtualization

When services are not virtualized, machines are physically separated. Any exploit is usually contained to the affected machine, with the obvious exception of network attacks. When services are grouped together in a virtualized environment, extra vulnerabilities emerge in the system. If there is a security flaw in the hypervisor that can be exploited by a guest instance, this guest may be able to not only attack the host, but also other guests running on that host. This is not theoretical; attacks already exist on hypervisors. These attacks can extend beyond the guest instance and could expose other guests to attack.
sVirt is an effort to isolate guests and limit their ability to launch further attacks if exploited. This is demonstrated in the following image, where an attack can not break out of the virtualized guest and extend to another host instance:
SELinux introduces a pluggable security framework for virtualized instances in its implementation of Mandatory Access Control (MAC). The sVirt framework allows guests and their resources to be uniquely labeled. Once labeled, rules can be applied which can reject access between different guests.

17.2. sVirt labeling

Like other services under the protection of SELinux, sVirt uses process-based mechanisms and restrictions to provide an extra layer of security over guest instances. Under typical use, you should not even notice that sVirt is working in the background. This section describes the labeling features of sVirt.
As shown in the following output, when using sVirt, each virtualized guest process is labeled and runs with a dynamically generated level. Each process is isolated from other VMs with different levels:
# ps -eZ | grep qemu

system_u:system_r:svirt_t:s0:c87,c520 27950 ?  00:00:17 qemu-kvm
system_u:system_r:svirt_t:s0:c639,c757 27989 ? 00:00:06 qemu-system-x86
The actual disk images are automatically labeled to match the processes, as shown in the following output:
# ls -lZ /var/lib/libvirt/images/*

  system_u:object_r:svirt_image_t:s0:c87,c520   image1
The following table outlines the different labels that can be assigned when using sVirt:
Table 17.1. sVirt labels
Type SELinux Context Description
Virtualized guest processes system_u:system_r:svirt_t:MCS1 MCS1 is a randomly selected MCS field. Currently approximately 500,000 labels are supported.
Virtualized guest images system_u:object_r:svirt_image_t:MCS1 Only svirt_t processes with the same MCS fields are able to read/write these image files and devices.
Virtualized guest shared read/write content system_u:object_r:svirt_image_t:s0 All svirt_t processes are allowed to write to the svirt_image_t:s0 files and devices.
Virtualized guest shared read only content system_u:object_r:svirt_content_t:s0 All svirt_t processes are able to read files/devices with this label.
Virtualized guest images system_u:object_r:virt_content_t:s0 System default label used when an image exits. No svirt_t virtual processes are allowed to read files/devices with this label.

It is also possible to perform static labeling when using sVirt. Static labels allow the administrator to select a specific label, including the MCS/MLS field, for a virtualized guest. Administrators who run statically-labeled virtualized guests are responsible for setting the correct label on the image files. The virtualized guest will always be started with that label, and the sVirt system will never modify the label of a statically-labeled virtual machine's content. This allows the sVirt component to run in an MLS environment. You can also run multiple virtualized guests with different sensitivity levels on a system, depending on your requirements.

Chapter 18. KVM live migration

This chapter covers migrating guests running on a KVM hypervisor to another KVM host.
Migration is the term for the process of moving a virtualized guest from one host to another. Migration is a key feature of virtualization as software is completely separated from hardware. Migration is useful for:
  • Load balancing - guests can be moved to hosts with lower usage when a host becomes overloaded.
  • Hardware failover - when hardware devices on the host start to fail, guests can be safely relocated so the host can be powered down and repaired.
  • Energy saving - guests can be redistributed to other hosts and host systems powered off to save energy and cut costs in low usage periods.
  • Geographic migration - guests can be moved to another location for lower latency or in serious circumstances.
Migrations can be performed live or offline. To migrate guests the storage must be shared. Migration works by sending the guests memory to the destination host. The shared storage stores the guest's default file system. The file system image is not sent over the network from the source host to the destination host.
An offline migration suspends the guest then moves an image of the guests memory to the destination host. The guest is resumed on the destination host and the memory the guest used on the source host is freed.
The time an offline migration takes depends on network bandwidth and latency. If the network is experiencing heavy use or low bandwidth the migration will take much longer.
A live migration keeps the guest running on the source host and begins moving the memory without stopping the guest. All modified memory pages are monitored for changes and sent to the destination while the image is sent. The memory is updated with the changed pages. The process continues until the amount of pause time allowed for the guest equals the predicted time for the final few pages to be transferred. KVM estimates the time remaining and attempts to transfer the maximum amount of page files from the source to the destination until KVM predicts the amount of remaining pages can be transferred during a very brief time while the virtualized guest is paused. The registers are loaded on the new host and the guest is then resumed on the destination host. If the guest cannot be merged (which happens when guests are under extreme loads) the guest is paused and then an offline migration is started instead.

18.1. Live migration requirements

Migrating guests requires the following:
Migration requirements
  • A virtualized guest installed on shared networked storage using one of the following protocols:
    • Fibre Channel
    • iSCSI
    • NFS
    • GFS2
  • Two or more Red Hat Enterprise Linux systems of the same version with the same updates.
  • Both systems must have the appropriate ports open.
  • Both systems must have identical network configurations. All bridging and network configurations must be exactly the same on both hosts.
  • Shared storage must mount at the same location on source and destination systems. The mounted directory name must be identical.
Configuring network storage
Configure shared storage and install a guest on the shared storage. For shared storage instructions, refer to Part V, “Virtualization storage topics”.

18.2. Shared storage example: NFS for a simple migration

This example uses NFS to share guest images with other KVM hosts. This example is not practical for large installations, this example is only for demonstrating migration techniques and small deployments. Do not use this example for migrating or running more than a few virtualized guests.
For advanced and more robust shared storage instructions, refer to Part V, “Virtualization storage topics”
  1. Export your libvirt image directory

    Add the default image directory to the /etc/exports file:
    /var/lib/libvirt/images *.example.com(rw,no_root_squash,async)
    
    Change the hosts parameter as required for your environment.
  2. Start NFS

    1. Install the NFS packages if they are not yet installed:
      # yum install nfs
      
    2. Open the ports for NFS in iptables and add NFS to the /etc/hosts.allow file.
    3. Start the NFS service:
      # service nfs start
      
  3. Mount the shared storage on the destination

    On the destination system, mount the /var/lib/libvirt/images directory:
    # mount sourceURL:/var/lib/libvirt/images /var/lib/libvirt/images
    

    Locations must be the same on source and destination

    Whichever directory is chosen for the guests must exactly the same on host and guest. This applies to all types of shared storage. The directory must be the same or the migration will fail.

18.3. Live KVM migration with virsh

A guest can be migrated to another host with the virsh command. The migrate command accepts parameters in the following format:
# virsh migrate --live GuestName DestinationURL
The GuestName parameter represents the name of the guest which you want to migrate.
The DestinationURL parameter is the URL or hostname of the destination system. The destination system must run the same version of Red Hat Enterprise Linux, be using the same hypervisor and have libvirt running.
Once the command is entered you will be prompted for the root password of the destination system.
Example: live migration with virsh
This example migrates from test1.example.com to test2.example.com. Change the host names for your environment. This example migrates a virtual machine named RHEL4test.
This example assumes you have fully configured shared storage and meet all the prerequisites (listed here: Migration requirements).
  1. Verify the guest is running

    From the source system, test1.example.com, verify RHEL4test is running:
    [[email protected] ~]# virsh list
    Id Name                 State
    ----------------------------------
     10 RHEL4                running
    
  2. Migrate the guest

    Execute the following command to live migrate the guest to the destination, test2.example.com. Append /system to the end of the destination URL to tell libvirt that you need full access.
    # virsh migrate --live RHEL4test qemu+ssh://test2.example.com/system
    Once the command is entered you will be prompted for the root password of the destination system.
  3. Wait

    The migration may take some time depending on load and the size of the guest. virsh only reports errors. The guest continues to run on the source host until fully migrated.
  4. Verify the guest has arrived at the destination host

    From the destination system, test2.example.com, verify RHEL4test is running:
    [[email protected] ~]# virsh list
    Id Name                 State
    ----------------------------------
     10 RHEL4                running
    
The live migration is now complete.

Other networking methods

libvirt supports a variety of networking methods including TLS/SSL, unix sockets, SSH, and unencrypted TCP. Refer to Chapter 19, Remote management of virtualized guests for more information on using other methods.

18.4. Migrating with virt-manager

This section covers migrating KVM based guests with virt-manager.
  1. Connect to the source and the target hosts

    Connect to the source and target hosts. On the File menu, click Add Connection, the Add Connection window appears.
    Enter the following details:
    • Hypervisor: Select QEMU.
    • Connection: Select the connection type.
    • Hostname: Enter the hostname.
    Press the Connect button.
    Add Connection
    Figure 18.1. Add Connection

    virt-manager now displays the newly connected host in the list of available hosts.
    Connected Host
    Figure 18.2. Connected Host

  2. Add a storage pool to both hosts

    Both hosts must be connected to the same storage pool. Create the storage pool on both hosts using the same network storage device. Using a storage pool ensures both servers have identical storage configurations. This procedure uses a NFS server.
    1. Open the storage tab

      On the Edit menu, click Host Details, the Host Details window appears.
      Click the Storage tab.
      Storage tab
      Figure 18.3. Storage tab

    2. Add a storage pool with the same NFS to the source and target hosts.

      Add a new storage pool. In the lower left corner of the window, click the + button. The Add a New Storage Pool window appears.
      Enter the following details:
      • Name: Enter the name of the storage pool.
      • Type: Select netfs: Network Exported Directory.
      Add a new Storage Pool
      Figure 18.4. Add a new Storage Pool

      Press Forward to continue.
    3. Specify storage pool details

      Enter the following details:
      • Format: Select the storage type. This must be NFS or iSCSI for live migrations.
      • Host Name: Enter the IP address or fully-qualified domain name of the storage server.
      Storage pool details
      Figure 18.5. Storage pool details

      Press the Finish button to add the storage pool.
    4. Verify the new storage pool was added sucessfully

      The new storage pool should be visible in the Storage tab.
      New storage pool in the storage tab
      Figure 18.6. New storage pool in the storage tab

    Complete these steps on both hosts before proceeding.
  3. Optional: Add a volume to the storage pool

    Add a volume to the storage pool or create a new virtualized guest on the storage pool. If your storage pool already has virtualized guests, you can skip this step.
    1. Create a new volume in the shared storage pool, click New Volume.
      Enter the details, then click Create Volume.
      Add a storage volume
      Figure 18.7. Add a storage volume

    2. Create a new virtualized guest on the new volume

      Create a new virtualized guest that uses the new volume. For information on creating virtualized guests, refer to Part II, “Installation”.
      New virtualized guest
      Figure 18.8. New virtualized guest

      The Virtual Machine window appears.
      Virtual Machine window
      Figure 18.9. Virtual Machine window

  4. Migrate the virtualized guest

    From the main virt-manager screen, right-click on the virtual machine and select Migrate.... The Migrate the virtual machine window appears.
    Migrate the virtual machine
    Figure 18.10. Migrate the virtual machine

    Select the destination host from the list.
    Select Migrate offline to disable live migration and do an offline migration.
    Select advanced options if required. For a standard migration, no of these settings should be modified.
    Press Migrate to confirm and migrate the virtualized guest.
  5. A status bar tracks the progress of the migration. Once the migration is complete the virtualized guest will appear in the list of virtualized guests on the destination.
    Completed migration
    Figure 18.11. Completed migration

Chapter 19. Remote management of virtualized guests

This section explains how to remotely manage your virtualized guests using ssh or TLS and SSL.

19.1. Remote management with SSH

The ssh package provides an encrypted network protocol which can securely send management functions to remote virtualization servers. The method described uses the libvirt management connection securely tunneled over an SSH connection to manage the remote machines. All the authentication is done using SSH public key cryptography and passwords or passphrases gathered by your local SSH agent. In addition the VNC console for each guest virtual machine is tunneled over SSH.
SSH is usually configured by default so you probably already have SSH keys setup and no extra firewall rules needed to access the management service or VNC console.
Be aware of the issues with using SSH for remotely managing your virtual machines, including:
  • you require root log in access to the remote machine for managing virtual machines,
  • the initial connection setup process may be slow,
  • there is no standard or trivial way to revoke a user's key on all hosts or guests, and
  • ssh does not scale well with larger numbers of remote machines.
Configuring password less or password managed SSH access for virt-manager
The following instructions assume you are starting from scratch and do not already have SSH keys set up. If you have SSH keys set up and copied to the other systems you can skip this procedure.

The user is important for remote management

SSH keys are user dependent. Only the user who owns the key may access that key.
virt-manager must run as the user who owns the keys to connect to the remote host. That means, if the remote systems are managed by a non-root user virt-manager must be run in unprivileged mode. If the remote systems are managed by the local root user then the SSH keys must be owned and created by root.
You cannot manage the local host as an unprivileged user with virt-manager.
  1. Optional: Changing user

    Change user, if required. This example uses the local root user for remotely managing the other hosts and the local host.
    $ su -
  2. Generating the SSH key pair

    Generate a public key pair on the machine virt-manager is used. This example uses the default key location, in the ~/.ssh/ directory.
    $ ssh-keygen -t rsa
  3. Copying the keys to the remote hosts

    Remote login without a password, or with a passphrase, requires an SSH key to be distributed to the systems being managed. Use the ssh-copy-id command to copy the key to root user at the system address provided (in the example, [email protected]).
    $ ssh-copy-id -i ~/.ssh/id_rsa.pub [email protected]
    [email protected]'s password:
    
    Now try logging into the machine, with the ssh [email protected] command and check in the .ssh/authorized_keys file to make sure unexpected keys have not been added.
    Repeat for other systems, as required.
  4. Optional: Add the passphrase to the ssh-agent

    Add the passphrase for the SSH key to the ssh-agent, if required. On the local host, use the following command to add the passphrase (if there was one) to enable password-less login.
    # ssh-add ~/.ssh/id_rsa.pub
The SSH key was added to the remote system.
The libvirt daemon (libvirtd)
The libvirt daemon provide an interface for managing virtual machines. You must have the libvirtd daemon installed and running on every remote host that needs managing.
$ ssh [email protected]somehost
# chkconfig libvirtd on
# service libvirtd start
After libvirtd and SSH are configured you should be able to remotely access and manage your virtual machines. You should also be able to access your guests with VNC at this point.
Accessing remote hosts with virt-manager
Remote hosts can be managed with the virt-manager GUI tool. SSH keys must belong to the user executing virt-manager for password-less login to work.
  1. Start virt-manager.
  2. Open the File->Add Connection menu.
  3. Input values for the hypervisor type, the connection, Connection->Remote tunnel over SSH, and enter the desired hostname, then click connection.

19.2. Remote management over TLS and SSL

You can manage virtual machines using TLS and SSL. TLS and SSL provides greater scalability but is more complicated than ssh (refer to Section 19.1, “Remote management with SSH”). TLS and SSL is the same technology used by web browsers for secure connections. The libvirt management connection opens a TCP port for incoming connections, which is securely encrypted and authenticated based on x509 certificates.
TLS/SSL access for virt-manager
The libvirt Wiki contains complete details on how to configure TLS/SSL access: http://wiki.libvirt.org/page/TLSSetup
To enable SSL and TLS for VNC, refer to the libvirt Wiki: http://wiki.libvirt.org/page/VNCTLSSetup. It is necessary to place the Certificate Authority Certificate, Client Certificate, and Client Certificate Private Key, in the following locations:
  • The Certificate Authority Certificate should be placed in /etc/pki/CA/cacert.pem.
  • The Client Certificate, signed by the CA, should be placed in either of:
    • /etc/pki/libvirt-vnc/clientcert.pem for system wide use, or
    • $HOME/.pki/libvirt-vnc/clientcert.pem for an individual user.
  • The Private Key for the Client Certificate should be placed in either of:
    • /etc/pki/libvirt-vnc/private/clientkey.pem for system wide use, or
    • $HOME/.pki/libvirt-vnc/private/clientkey.pem for an individual user.

19.3. Transport modes

For remote management, libvirt supports the following transport modes:
Transport Layer Security (TLS)
Transport Layer Security TLS 1.0 (SSL 3.1) authenticated and encrypted TCP/IP socket, usually listening on a public port number. To use this you will need to generate client and server certificates. The standard port is 16514.
UNIX sockets
Unix domain sockets are only accessible on the local machine. Sockets are not encrypted, and use UNIX permissions or SELinux for authentication. The standard socket names are /var/run/libvirt/libvirt-sock and /var/run/libvirt/libvirt-sock-ro (for read-only connections).
SSH
Transported over a Secure Shell protocol (SSH) connection. Requires Netcat (the nc package) installed. The libvirt daemon (libvirtd) must be running on the remote machine. Port 22 must be open for SSH access. You should use some sort of ssh key management (for example, the ssh-agent utility) or you will be prompted for a password.
ext
The ext parameter is used for any external program which can make a connection to the remote machine by means outside the scope of libvirt. This parameter is unsupported.
tcp
Unencrypted TCP/IP socket. Not recommended for production use, this is normally disabled, but an administrator can enable it for testing or use over a trusted network. The default port is 16509.
The default transport, if no other is specified, is tls.
Remote URIs
A Uniform Resource Identifier (URI) is used by virsh and libvirt to connect to a remote host. URIs can also be used with the --connect parameter for the virsh command to execute single commands or migrations on remote hosts.
libvirt URIs take the general form (content in square brackets, "[]", represents optional functions):
driver[+transport]://[[email protected]][hostname][:port]/[path][?extraparameters]
The transport method or the hostname must be provided to target an external location.
Examples of remote management parameters
  • Connect to a remote KVM host named server7, using SSH transport and the SSH username ccurran.
    qemu+ssh://[email protected]/
    
  • Connect to a remote KVM hypervisor on the host named server7 using TLS.
    qemu://server7/
    
  • Connect to a remote KVM hypervisor on host server7 using TLS. The no_verify=1 instructs libvirt not to verify the server's certificate.
    qemu://server7/?no_verify=1
    
Testing examples
  • Connect to the local KVM hypervisor with a non-standard UNIX socket. The full path to the Unix socket is supplied explicitly in this case.
    qemu+unix:///system?socket=/opt/libvirt/run/libvirt/libvirt-sock
    
  • Connect to the libvirt daemon with an unencrypted TCP/IP connection to the server with the IP address 10.1.1.10 on port 5000. This uses the test driver with default settings.
    test+tcp://10.1.1.10:5000/default
    
Extra URI parameters
Extra parameters can be appended to remote URIs. The table below Table 19.1, “Extra URI parameters” covers the recognized parameters. All other parameters are ignored. Note that parameter values must be URI-escaped (that is, a question mark (?) is appended before the parameter and special characters are converted into the URI format).
Table 19.1. Extra URI parameters
Name Transport mode Description Example usage
name all modes The name passed to the remote virConnectOpen function. The name is normally formed by removing transport, hostname, port number, username and extra parameters from the remote URI, but in certain very complex cases it may be better to supply the name explicitly. name=qemu:///system
command ssh and ext The external command. For ext transport this is required. For ssh the default is ssh. The PATH is searched for the command. command=/opt/openssh/bin/ssh
socket unix and ssh The path to the UNIX domain socket, which overrides the default. For ssh transport, this is passed to the remote netcat command (see netcat). socket=/opt/libvirt/run/libvirt/libvirt-sock
netcat ssh
The netcat command can be used to connect to remote systems. The default netcat parameter uses the nc command. For SSH transport, libvirt constructs an SSH command using the form below:
command -p port [-l username] hostname
netcat -U socket
The port, username and hostname parameters can be specified as part of the remote URI. The command, netcat and socket come from other extra parameters.
netcat=/opt/netcat/bin/nc
no_verify tls If set to a non-zero value, this disables client checks of the server's certificate. Note that to disable server checks of the client's certificate or IP address you must change the libvirtd configuration. no_verify=1
no_tty ssh If set to a non-zero value, this stops ssh from asking for a password if it cannot log in to the remote machine automatically (for using ssh-agent or similar). Use this when you do not have access to a terminal - for example in graphical programs which use libvirt. no_tty=1

Chapter 20. Overcommitting with KVM

The KVM hypervisor supports overcommitting CPUs and overcommitting memory. Overcommitting is allocating more virtualized CPUs or memory than there are physical resources on the system. With CPU overcommit, under-utilized virtualized servers or desktops can run on fewer servers which saves power and money.
Overcommitting memory
Most operating systems and applications do not use 100% of the available RAM all the time. This behavior can be exploited with KVM. KVM can allocate more memory for virtualized guests than the host has physically available.
With KVM, virtual machines are Linux processes. Guests on the KVM hypervisor do not have dedicated blocks of physical RAM assigned to them, instead guests function as Linux processes. The Linux kernel allocates each process memory when the process requests more memory. KVM guests are allocated memory when requested by the guest operating system. The guest only requires slightly more physical memory than the virtualized operating system reports as used. The Linux kernel swaps infrequently used memory out of physical memory and into virtual memory. Swapping decreases the amount of memory required by virtualized guests.
When physical memory is completely used or a process is inactive for some time, Linux moves the process's memory to swap. Swap is usually a partition on a hard disk drive or solid state drive which Linux uses to extend virtual memory. Swap is significantly slower than RAM due to the throughput and response times of hard drives and solid state drives.
As KVM virtual machines are Linux processes, underused or idle memory of virtualized guests is moved by default to swap. The total memory used by guests can be overcommitted, which is to use more than the physically available host memory. Overcommitting requires sufficient swap space for all guests and all host processes.
Without sufficient swap space for all processes in virtual memory the pdflush process, the cleanup process, starts. The pdflush process kills processes to free memory so the system does not crash. pdflush may destroy virtualized guests or other system processes which may cause file system errors and may leave virtualized guests unbootable.This can cause issues if virtualized guests use their total RAM.

Warning

If sufficient swap is not available guest operating systems will be forcibly shut down. This may leave guests inoperable. Avoid this by never overcommitting more memory than there is swap available.

Overcommitting with KSM

If KSM is used ensure the swap size is sufficient for the overcommitted RAM. KSM reduces the RAM usage of identical or similar guests. Overcommitting guests with KSM without sufficient swap may be possible but is not recommended. For more information on KSM and overcommitting, refer to Chapter 21, KSM.
Configuring swap for overcommitting memory
The swap partition is used for swapping underused memory to the hard drive to speed up memory performance. The default size of the swap partition is calculated from the physical RAM of the host.
Red Hat Knowledgebase has an article on safely and efficiently determining the size of the swap partition.
The swap partition must be large enough to provide virtual memory for all guests and the host system.

Important

The example below is provided as a guide for configuring swap only. The settings listed may not be appropriate for your environment.
Example 20.1. Memory overcommit example
ExampleServer1 has 32GB of RAM. The system is being configured to run 56 guests with 1GB of virtualized memory. The host system rarely uses more than 4GB of memory for system processes, drivers and storage caching.
32GB minus 4GB for the host leaves 28GB of physical RAM for virtualized guests. Each guest uses 1GB of RAM, a total of 56GB of virtual RAM is required for the guests.
The Red Hat Knowledgebase recommends 8GB of swap for a system with 32GB of RAM. To safely overcommit memory there must be sufficient virtual memory for all guests and the host. The host has 28GB of RAM for guests (which need 56GB of RAM). Therefore, the system needs at least 28GB of swap for the guests.
ExampleServer1 requires at least 36GB (8GB for the host and 28GB for the guests) of swap to safely overcommit for all 56 guests.

It is possible to overcommit memory over ten times the amount of physical RAM in the system. This only works with certain types of guest, for example, desktop virtualization with minimal intensive usage or running several identical guests with KSM. Configuring swap and memory overcommit is not a formula, each environment and setup is different. Your environment must be tested and customized to ensure stability and performance.
For more information on KSM and overcommitting, refer to Chapter 21, KSM.
Overcommitting virtualized CPUs
The KVM hypervisor supports overcommitting virtualized CPUs. Virtualized CPUs can be overcommitted as far as load limits of virtualized guests allow. Use caution when overcommitting VCPUs as loads near 100% may cause dropped requests or unusable response times.
Virtualized CPUs are overcommitted best when each virtualized guest only has a single VCPU. The Linux scheduler is very efficient with this type of load. KVM should safely support guests with loads under 100% at a ratio of five VCPUs. Overcommitting single VCPU virtualized guests is not an issue.
You cannot overcommit symmetric multiprocessing guests on more than the physical number of processing cores. For example a guest with four VCPUs should not be run on a host with a dual core processor. Overcommitting symmetric multiprocessing guests in over the physical number of processing cores will cause significant performance degradation.
Assigning guests VCPUs up to the number of physical cores is appropriate and works as expected. For example, running virtualized guests with four VCPUs on a quad core host. Guests with less than 100% loads should function effectively in this setup.

Always test first

Do not overcommit memory or CPUs in a production environment without extensive testing. Applications which use 100% of memory or processing resources may become unstable in overcommitted environments. Test before deploying.

Chapter 21. KSM

The concept of shared memory is common in modern operating systems. For example, when a program is first started it shares all of its memory with the parent program. When either the child or parent program tries to modify this memory, the kernel allocates a new memory region, copies the original contents and allows the program to modify this new region. This is known as copy on write.
KSM is a new Linux feature which uses this concept in reverse. KSM enables the kernel to examine two or more already running programs and compare their memory. If any memory regions or pages are identical, KSM reduces multiple references to multiple identical memory pages to a single reference to a single page. This page is then marked copy on write. If the contents of the page is modified, a new page is created.
This is useful for virtualization with KVM. When a virtualized guest is started, it only inherits the memory from the parent qemu-kvm process. Once the guest is running the contents of the guest operating system image can be shared when guests are running the same operating system or applications. KSM only identifies and merges identical pages which does not interfere with the guest or impact the security of the host or the guests. KSM allows KVM to request that these identical guest memory regions be shared.
KSM provides enhanced memory speed and utilization. With KSM, common process data is stored in cache or in main memory. This reduces cache misses for the KVM guests which can improve performance for some applications and operating systems. Secondly, sharing memory reduces the overall memory usage of guests which allows for higher densities and greater utilization of resources.
Red Hat Enterprise Linux uses two separate methods for controlling KSM:
  • The ksm service starts and stops the KSM kernel thread.
  • The ksmtuned service controls and tunes the ksm, dynamically managing same-page merging. The ksmtuned service starts ksm and stops the ksm service if memory sharing is not necessary. The ksmtuned service must be told with the retune parameter to run when new virtualized guests are created or destroyed.
Both of these services are controlled with the standard service management tools.
The KSM service
The ksm service is a standard Linux daemon that uses the KSM kernel features.
KSM is included in the qemu-common package, which is a dependency of KVM. KSM is enabled by default in Red Hat Enterprise Linux. When the ksm service is not started, KSM shares only 2000 pages. This default is low and provides limited memory saving benefits.
When the ksm service is started, KSM will share up to half of the host system's main memory. Start the ksm service to enable KSM to share more memory.
# service ksm start
Starting ksm:                                              [  OK  ]
The ksm service can be added to the default startup sequence. Make the ksm service persistent with the chkconfig command.
# chkconfig ksm on
The KSM tuning service
The ksmtuned service does not have any options. The ksmtuned service loops and adjusts ksm. The ksmtuned service is notified by libvirt when a virtualized guest is created or destroyed.
# service ksmtuned start
Starting ksmtuned:                                         [  OK  ]
The ksmtuned service can be tuned with the retune parameter. The retune parameter instructs ksmtuned to run tuning functions manually.
The /etc/ksmtuned.conf file is the configuration file for the ksmtuned service. The file output below is the default ksmtuned.conf file.
# Configuration file for ksmtuned.

# How long ksmtuned should sleep between tuning adjustments
# KSM_MONITOR_INTERVAL=60

# Millisecond sleep between ksm scans for 16Gb server.
# Smaller servers sleep more, bigger sleep less.
# KSM_SLEEP_MSEC=10

# KSM_NPAGES_BOOST=300
# KSM_NPAGES_DECAY=-50
# KSM_NPAGES_MIN=64
# KSM_NPAGES_MAX=1250

# KSM_THRES_COEF=20
# KSM_THRES_CONST=2048

# uncomment the following to enable ksmtuned debug information
# LOGFILE=/var/log/ksmtuned
# DEBUG=1
KSM variables and monitoring
KSM stores monitoring data in the /sys/kernel/mm/ksm/ directory. Files in this directory are updated by the kernel and are an accurate record of KSM usage and statistics.
The variables in the list below are also configurable variables in the /etc/ksmtuned.conf file as noted below.
The /sys/kernel/mm/ksm/ files
full_scans
Full scans run.
pages_shared
Total pages shared.
pages_sharing
Pages presently shared.
pages_to_scan
Pages not scanned.
pages_unshared
Pages no longer shared.
pages_volatile
Number of volatile pages.
run
Whether the KSM process is running.
sleep_millisecs
Sleep milliseconds.
KSM tuning activity is stored in the /var/log/ksmtuned log file if the DEBUG=1 line is added to the /etc/ksmtuned.conf file. The log file location can be changed with the LOGFILE parameter. Changing the log file location is not advised and may require special configuration of SELinux settings.
The /etc/sysconfig/ksm file can manually set a number or all pages used by KSM as not swappable.
  1. Open the /etc/sysconfig/ksm file with a text editor.
    # The maximum number of unswappable kernel pages
    # which may be allocated by ksm (0 for unlimited)
    # If unset, defaults to half of total memory
    # KSM_MAX_KERNEL_PAGES=
  2. Uncomment the KSM_MAX_KERNEL_PAGES line to manually configure the number of unswappable pages for KSM. Setting this variable to 0 configures KSM to keep all identical pages in main memory which can improve performance if the system has sufficient main memory.
    # The maximum number of unswappable kernel pages
    # which may be allocated by ksm (0 for unlimited)
    # If unset, defaults to half of total memory
    KSM_MAX_KERNEL_PAGES=0
Deactivating KSM
KSM has a performance overhead which may be too large for certain environments or host systems.
KSM can be deactivated by stopping the ksm service and the ksmtuned service. Stopping the services deactivates KSM but does not persist after restarting.
# service ksm stop
Stopping ksm:                                              [  OK  ]
# service ksmtuned stop
Stopping ksmtuned:                                         [  OK  ]
Persistently deactivate KSM with the chkconfig command. To turn off the services, run the following commands:
# chkconfig ksm off
# chkconfig ksmtuned off

Chapter 22. Advanced virtualization administration

This chapter covers advanced administration tools for fine tuning and controlling virtualized guests and host system resources.

Note

This chapter is a work in progress. Refer back to this document at a later date.

22.1. Guest scheduling

KVM guests function as Linux processes. By default, KVM guests are prioritized and scheduled with the Linux Completely Fair Scheduler. Tuning the schedule for guest processes may be required for some environments or to prioritize certain guests.

22.2. Advanced memory management

Capping memory available to guests and preventing overcommit on certain guests.

22.3. Guest block I/O throttling

Limit guest block I/O throughput.

22.4. Guest network I/O throttling

Limit guest network activity.

Chapter 23. Migrating to KVM from other hypervisors using virt-v2v

The virt-v2v command converts guests from a foreign hypervisor to run on KVM, managed by libvirt. The virt-v2v command can currently convert Red Hat Enterprise Linux 4, Red Hat Enterprise Linux 5, Windows Vista, Windows 7, Windows Server 2003 and Windows Server 2008 virtualized guests running on Xen, KVM and VMware ESX. The virt-v2v command enables para-virtualized (virtio) drivers in the converted guest if possible.
virt-v2v is available on Red Hat Network (RHN) in the Red Hat Enterprise Linux Server (v. 6 for 64-bit x86_64) or Red Hat Enterprise Linux Workstation (v.6 for x86_64) channel.
The virt-v2v tool requires root access to the host system.
Installing virt-v2v
To install virt-v2v from RHN, ensure the system is subscribed to the appropriate channel, then run:
yum install virt-v2v

23.1. Preparing to convert a virtualized guest

Before a virtualized guest can be converted, ensure that the following steps are completed.
  1. Create a local storage domain for transferred storage
    virt-v2v copies the guest storage to a locally defined libvirt storage pool during import. This pool can be defined using any libvirt tool, and can be of any type. The simplest way to create a new pool is with virt-manager. Select your host, right click and select details.
    Select host details
    Figure 23.1. Select host details

    Select the Storage tab.
    The storage tab
    Figure 23.2. The storage tab

    Click the plus sign (+) button to add a new storage pool.
    Adding a storage pool
    Figure 23.3. Adding a storage pool

  2. Create local network interfaces.
    The local machine must have an appropriate network to which the converted virtualized guest can connect. This is likely to be a bridge interface. A bridge interface can be created using standard tools on the host. Since version 0.8.3, virt-manager can also create and manage bridges.
  3. Specify network mappings in virt-v2v.conf. This step is optional, and is not required for most use cases.
    If your virtualized guest has multiple network interfaces, /etc/virt-v2v.conf must be edited to specify the network mapping for all interfaces. You can specify an alternative virt-v2v.conf file with the -f parameter.
    If your virtualized guest only has a single network interface, it is simpler to use the --network or --bridge parameters, rather than modifying virt-v2v.conf.
Preparing to convert a virtualized guest running Linux
Before a virtualized guest running Linux can be converted, ensure that the following steps are completed.
  1. Obtain the software
    As part of the conversion process, virt-v2v may install a new kernel and drivers on the virtualized guest. If the host running virt-v2v is registered to Red Hat Network (RHN), the required packages will be automatically downloaded. For environments where RHN is not available, the virt-v2v.conf file references a list of RPMs used for this purpose. The RPMs relevant to your virtualized guest must be downloaded manually from RHN and made available in the directory specified by the path-root configuration element, which by default is /var/lib/virt-v2v/software/. virt-v2v will display an error similar to Example 23.1, “Missing Package error” if software it depends upon for a particular conversion is not available.
    Example 23.1. Missing Package error
    virt-v2v: Installation failed because the following files referenced in the configuration file are required, but missing:
    rhel/5/kernel-2.6.18-128.el5.x86_64.rpm
    rhel/5/ecryptfs-utils-56-8.el5.x86_64.rpm
    rhel/5/ecryptfs-utils-56-8.el5.i386.rpm

    To obtain the relevant RPMs for your environment, repeat these steps for each missing package:
    1. Login to Red Hat Network
    2. Select Channels
    3. Use the Filter by Product Channel function to select the channel for the version of Red Hat Enterprise Linux running on the virtualized guest. In the case of the example shown in Example 23.1, “Missing Package error”, the channel is Red Hat Enterprise Linux Server 5.3.
    4. Select the Packages tab
    5. Use the Filter by Package function to locate the missing package
    6. Select the package exactly matching the one shown in the error message. For the the example shown in Example 23.1, “Missing Package error”, the first package is kernel-2.6.18-128.el5.x86_64
    7. Select Download Package at the bottom of the package details page
    8. Save the downloaded package to the appropriate directory in /var/lib/virt-v2v/software. For Red Hat Enterprise Linux 5, the directory is /var/lib/virt-v2v/software/rhel/5
Preparing to convert a virtualized guest running Windows
Before a virtualized guest running Windows can be converted, ensure that the following steps are completed.

Important

Virtualized guests running Windows can only be converted for output to Red Hat Enterprise Virtualization. The conversion procedure depends on post-processing by the Red Hat Enterprise Virtualization Manager for completion. See Section 23.4.2, “Configuration changes for Windows virtualized guests” for details of the process. Virtualized guests running Windows cannot be converted for output to libvirt.
  1. Obtain the Guest Tools ISO
    As part of the conversion process for virtualized guests running Windows, the Red Hat Enterprise Virtualization Manager will install drivers using the Guest Tools ISO. See Section 23.4.2, “Configuration changes for Windows virtualized guests” for details of the process. The Guest Tools ISO is obtained as follows:
    1. From the Red Hat Enterprise Virtualization Manager, Login to Red Hat Network
    2. Click on Download Software
    3. Select the Red Hat Enterprise Virtualization (x86-64) channel
    4. Select the Red Hat Enterprise Virt Manager for Desktops (v.2 x86) or Red Hat Enterprise Virt Manager for Desktops (v.2 x86) channel, as appropriate for your subscription.
    5. Download Guest Tools ISO for 2.2 and save it locally
  2. Upload the Guest Tools ISO to the Red Hat Enterprise Virtualization Manager
    Upload the Guest Tools ISO using the ISO Uploader. See the Red Hat Enterprise Virtualization for Servers Administration Guide for instructions.
  3. Ensure that the libguestfs-winsupport package is installed on the host running virt-v2v. This package provides support for NTFS, which is used by many Windows systems. If you attempt to convert a virtualized guest using NTFS without the libguestfs-winsupport package installed, the conversion will fail.
  4. Ensure that the virtio-win package is installed on the host running virt-v2v. This package provides para-virtualized block and network drivers for Windows guests. If you attempt to convert a virtualized guest running Windows without the virtio-win package installed, the conversion will fail giving an error message concerning missing files.
Preparing to convert a local Xen virtualized guest
The following is required when converting virtualized guests on a host which used to run Xen, but has been updated to run KVM. It is not required when converting a Xen guest imported directly from a running libvirt/Xen instance.
  1. Obtain the XML for the virtualized guest
    virt-v2v uses a libvirt domain description to determine the current configuration of the virtualized guest, including the location of its storage. Before starting the conversion, obtain this from the host running the virtualized guest with the following command:
    virsh dumpxml vm-name > vm-name.xml
    This will require booting into a Xen kernel to obtain the XML, as libvirt needs to connect to a running Xen hypervisor to obtain its metadata. The conversion process is optimized for KVM, so obtaining domain data while running a Xen kernel, then performing the conversion using a KVM kernel will be more efficient than running the conversion on a Xen kernel.

23.2. Converting virtualized guests

Once you have prepared to convert the virtualized guests, use virt-v2v to perform the actual conversions. This section provides the steps to convert the virtualized guests, and the reference table for virt-v2v. Note that conversions are resource intensive processes, involving copying the whole disk image for a virtualized guest. In typical environments, converting a single virtualized guest takes approximately 5-10 minutes.

23.2.1. virt-v2v

virt-v2v converts guests from a foreign hypervisor to run on KVM, managed by libvirt.
virt-v2v -i libvirtxml -op pool --bridge brname vm-name.xml
virt-v2v -op pool --network netname vm-name
virt-v2v -ic esx://esx.example.com/?no_verify=1 -op pool --bridge brname vm-name
Parameters
-i input
Specifies the input method to obtain the guest for conversion. The default is libvirt. Supported options are:
  • libvirt Guest argument is the name of a libvirt domain.
  • libvirtxml Guest argument is the path to an XML file containing a libvirt domain.
-ic URI
Specifies the connection to use when using the libvirt input method. If omitted, this defaults to qemu:///system.
virt-v2v can currently automatically obtain guest storage from local libvirt connections, ESX connections, and connections over SSH. Other types of connection are not supported.
-o method
Specifies the output method. If no output method is specified, the default is libvirt. Supported output methods are:
  • libvirt, create a libvirt guest. See the -oc and -op options. -op must be specified for the libvirt output method.
  • rhev, create a guest on a Red Hat Enterprise Virtualization Export storage domain, which can later be imported using the manager. The -osd or Export storage domain must be specified for the rhev output method.
-oc URI
Specifies the libvirt connection to use to create the converted guest. If omitted, this defaults to qemu:///system. Note that virt-v2v must be able to write directly to storage described by this libvirt connection. This makes writing to a remote connection impractical at present.
-op pool
Specifies the pool which will be used to create new storage for the converted guest.
-osd domain
Specifies the path to an existing Red Hat Enterprise Virtualization Export storage domain.
The domain must be in the format <host > <path>; for example, storage.example.com:/rhev/export. The nfs export must be mountable and writable by the machine running virt-v2v.
-f file | --config file Load the virt-v2v configuration from file. Defaults to /etc/virt-v2v.conf if it exists.
-n network | --network network
Map all guest bridges or networks which don't have a mapping in the configuration file to the specified network.
This option cannot be used in conjunction with --bridge.
-b bridge | --bridge bridge
Map all guest bridges or networks which don't have a mapping in the configuration file to the specified bridge.
This option cannot be used in conjunction with --network.
--help Display brief help.
--version Display version number and exit.

23.2.2. Converting a local Xen virtualized guest

Ensure that the virtualized guest's XML is available locally, and that the storage referred to in the XML is available locally at the same paths.
To convert the virtualized guest from an XML file, run:
virt-v2v -i libvirtxml -op pool --bridge brname vm-name.xml
Where pool is the local storage pool to hold the image, brname is the name of a local network bridge to connect the converted guest's network to, and vm-name.xml is the path to the virtualized guest's exported XML. You may also use the --network parameter to connect to a locally managed network, or specify multiple mappings in /etc/virt-v2v.conf.
If your guest uses a Xen para-virtualized kernel (it would be called something like kernel-xen or kernel-xenU), virt-v2v will attempt to install a new kernel during the conversion process. You can avoid this requirement by installing a regular kernel, which won't reference a hypervisor in its name, alongside the Xen kernel prior to conversion. You should not make this newly installed kernel your default kernel, because Xen will not boot it. virt-v2v will make it the default during conversion.

23.2.3. Converting a remote Xen virtualized guest

Xen virtualized guests can be converted remotely via SSH. Ensure that the host running the virtualized guest is accessible via SSH.
To convert the virtualized guest, run:
virt-v2v -ic xen+ssh://[email protected] -op pool --bridge brname vm-name
Where vmhost.example.com is the host running the virtualized guest, pool is the local storage pool to hold the image, brname is the name of a local network bridge to connect the converted guest's network to, and vm-name is the domain of the Xen virtualized guest. You may also use the --network parameter to connect to a locally managed network, or specify multiple mappings in /etc/virt-v2v.conf.
If your guest uses a Xen para-virtualized kernel (it would be called something like kernel-xen or kernel-xenU), virt-v2v will attempt to install a new kernel during the conversion process. You can avoid this requirement by installing a regular kernel, which won't reference a hypervisor in its name, alongside the Xen kernel prior to conversion. You should not make this newly installed kernel your default kernel, because Xen will not boot it. virt-v2v will make it the default during conversion.

23.2.4. Converting a VMware ESX virtualized guest

Ensure that the virtualized guest is stopped prior to running the v2v process.
To convert the virtualized guest, run:
virt-v2v -ic esx://esx.example.com/ -op pool --bridge brname vm-name
Where esx.example.com is the VMware ESX server, pool is the local storage pool to hold the image, brname is the name of a local network bridge to connect the converted guest's network to, and vm-name is the name of the virtualized guest. You may also use the --network parameter to connect to a locally managed network, or specify multiple mappings in /etc/virt-v2v.conf.
Authenticating to the ESX server
Connecting to the ESX server will require authentication. virt-v2v supports password authentication when connecting to ESX. It reads passwords from $HOME/.netrc. The format of this file is described in the netrc(5) man page. An example entry is:
machine esx.example.com login root password s3cr3t

.netrc permissions

The .netrc file must have a permission mask of 0600 to be read correctly by virt-v2v
Connecting to an ESX server with an invalid certificate
In non-production environments, the ESX server may have a non-valid certificate, for example a self-signed certificate. In this case, certificate checking can be explicitly disabled by adding '?no_verify=1' to the connection URI as shown below:
... -ic esx://esx.example.com/?no_verify=1 ...

23.2.5. Converting a virtualized guest running Windows

Important

Virtualized guests running Windows can only be converted for output to Red Hat Enterprise Virtualization. The conversion procedure depends on post-processing by the Red Hat Enterprise Virtualization Manager for completion. See Section 23.4.2, “Configuration changes for Windows virtualized guests” for details of the process. Virtualized guests running Windows cannot be converted for output to libvirt.
This example demonstrates converting a local Xen virtualized guest running Windows for output to Red Hat Enterprise Virtualization. Ensure that the virtualized guest's XML is available locally, and that the storage referred to in the XML is available locally at the same paths.
To convert the virtualized guest from an XML file, run:
virt-v2v -i libvirtxml -o rhev -osd storage.example.com:/exportdomain --network rhevm vm-name.xml
Where vm-name.xml is the path to the virtualized guest's exported xml, and storage.example.com:/exportdomain is the export storage domain. You may also use the --network parameter to connect to a locally managed network, or specify multiple mappings in /etc/virt-v2v.conf.
If your guest uses a Xen para-virtualized kernel (it would be called something like kernel-xen or kernel-xenU), virt-v2v will attempt to install a new kernel during the conversion process. You can avoid this requirement by installing a regular kernel, which won't reference a hypervisor in its name, alongside the Xen kernel prior to conversion. You should not make this newly installed kernel your default kernel, because Xen will not boot it. virt-v2v will make it the default during conversion.

23.3. Running converted virtualized guests

On successful completion, virt-v2v will create a new libvirt domain for the converted virtualized guest with the same name as the original virtualized guest. It can be started as usual using libvirt tools, for example virt-manager.
Guest network configuration
virt-v2v cannot currently reconfigure a guest's network configuration. If the converted guest is not connected to the same subnet as the source, its network configuration may have to be updated.

23.4. Configuration changes

As well as configuring libvirt appropriately, virt-v2v will make certain changes to a guest to enable it to run on a KVM hypervisor either with or without virtio drivers. These changes are specific to the guest operating system. The details specified here pertain to supported Red Hat based Linux distributions and Windows.

23.4.1. Configuration changes for Linux virtualized guests

Table 23.1. virt-v2v changes to Linux virtualized guests
Change Description
Kernel Un-bootable, that is, xen para-virtualized, kernels will be uninstalled. No new kernel will be installed if there is a remaining kernel which supports virtio. If no remaining kernel supports virtio and the configuration file specifies a new kernel it will be installed and configured as the default.
X reconfiguration If the guest has X configured, its display driver will be updated. See GUEST DRIVERS for which driver will be used.
Rename block devices If changes have caused block devices to change name, these changes will be reflected in /etc/fstab
Configure device drivers Whether virtio or non-virtio drivers are configured, virt-v2v will ensure that the correct network and block drivers are specified in the modprobe configuration.
initrd virt-v2v will ensure that the initrd for the default kernel supports booting the root device, whether it is using virtio or not.
SELinux virt-v2v will initiate a relabel of the guest on the next boot. This ensures that any changes it has made are correctly labeled according to the guest's local policy.

virt-v2v will configure the following drivers in a Linux guest:
Table 23.2. Configured drivers in a Linux Guest
Para-virtualized driver type Driver module
Display cirrus
Storage virtio_blk
Network virtio_net
In addition, initrd will preload the virtio_pci driver  
Other drivers
Display cirrus
Block Virtualized IDE
Network Virtualized e1000

23.4.2. Configuration changes for Windows virtualized guests

Warning

Before converting Windows virtualized guests, ensure that the libguestfs-winsupport and virtio-win packages are installed on the host running virt-v2v. These packages provide support for NTFS and Windows para-virtualized block and network drivers. If you attempt to convert a virtualized guest using NTFS without the libguestfs-winsupport package installed, the conversion will fail. If you attempt to convert a virtualized guest running Windows without the virtio-win package installed, the conversion will fail giving an error message concerning missing files.
virt-v2v can convert virtualized guests running Windows Vista, Windows 7, Windows Server 2003 and Windows Server 2008. The conversion process for virtualized guests running Windows is slightly to different to the process for virtualized guests running Linux. Windows virtualized guest images are converted as follows:
  1. virt-v2v installs virtio block drivers.
  2. virt-v2v installs the CDUpgrader utility.
  3. virt-v2v makes registry changes to include the virtio block drivers in the CriticalDeviceDatabase section of the registry, and ensure the CDUpgrader service is started at the next boot.
At this point, virt-v2v has completed the conversion. The converted virtualized guest is now bootable, but does not yet have all the drivers installed necessary to function correctly. The conversion must be finished by the Red Hat Enterprise Virtualization Manager. The Manager performs the following steps:
  1. The virtualized guest is imported and run on the Manager. See the Red Hat Enterprise Virtualization for Servers Administration Guide for details.

    Important

    The first boot stage can take several minutes to run, and must not be interrupted. It will run automatically without any administrator intervention other than starting the virtualized guest. To ensure the process is not interrupted, no user should login to the virtualized guest until it has quiesced. You can check for this in the Manager GUI.
  2. The Manager attaches the Guest Tools CD to the virtual machine.

    Note

    The Guest Tools ISO must be uploaded using the ISO Uploader for this step to succeed. See Preparing to convert a virtualized guest running Windows for instructions.
  3. CDUpgrader detects the Guest Tools CD and installs all the virtio drivers from it, including a re-install of the virtio block drivers.

Chapter 24. Miscellaneous administration tasks

This chapter contain useful hints and tips to improve virtualization performance, scale and stability.

24.1. Automatically starting guests

This section covers how to make virtualized guests start automatically during the host system's boot phase.
This example uses virsh to set a guest, TestServer, to automatically start when the host boots.
# virsh autostart TestServer
Domain TestServer marked as autostarted
The guest now automatically starts with the host.
To stop a guest automatically booting use the --disable parameter
# virsh autostart --disable TestServer
Domain TestServer unmarked as autostarted
The guest no longer automatically starts with the host.

24.2. Using qemu-img

The qemu-img command line tool is used for formatting various file systems used by KVM. qemu-img should be used for formatting virtualized guest images, additional storage devices and network storage. qemu-img options and usages are listed below.
Formatting and creating new images or devices
Create the new disk image filename of size size and format format.
# qemu-img create [-6] [-e] [-b base_image] [-f format] filename [size]
If base_image is specified, then the image will record only the differences from base_image. No size needs to be specified in this case. base_image will never be modified unless you use the "commit" monitor command.
Convert an existing image to another format
The convert option is used for converting a recognized format to another image format.
Command format:
# qemu-img convert [-c] [-e] [-f format] filename [-O output_format] output_filename
Convert the disk image filename to disk image output_filename using format output_format. The disk image can be optionally encrypted with the -e option or compressed with the -c option.
Only the qcow2 format supports encryption or compression. the compression is read-only. It means that if a compressed sector is rewritten, then it is rewritten as uncompressed data.
The encryption uses the AES format with very secure 128-bit keys. Use a long password (over 16 characters) to get maximum protection.
Image conversion is also useful to get smaller image when using a format which can grow, such as qcow or cow. The empty sectors are detected and suppressed from the destination image.
getting image information
the info parameter displays information about a disk image. the format for the info option is as follows:
# qemu-img info [-f format] filename
give information about the disk image filename. use it in particular to know the size reserved on disk which can be different from the displayed size. if vm snapshots are stored in the disk image, they are displayed too.
Supported formats
The format of an image is usually guessed automatically. The following formats are supported:
raw
Raw disk image format (default). This format has the advantage of being simple and easily exportable to all other emulators. If your file system supports holes (for example in ext2 or ext3 on Linux or NTFS on Windows), then only the written sectors will reserve space. Use qemu-img info to know the real size used by the image or ls -ls on Unix/Linux.
qcow2
QEMU image format, the most versatile format. Use it to have smaller images (useful if your file system does not supports holes, for example: on Windows), optional AES encryption, zlib based compression and support of multiple VM snapshots.
qcow
Old QEMU image format. Only included for compatibility with older versions.
cow
User Mode Linux Copy On Write image format. The cow format is included only for compatibility with previous versions. It does not work with Windows.
vmdk
VMware 3 and 4 compatible image format.
cloop
Linux Compressed Loop image, useful only to reuse directly compressed CD-ROM images present for example in the Knoppix CD-ROMs.

24.3. Verifying virtualization extensions

Use this section to determine whether your system has the hardware virtualization extensions. Virtualization extensions (Intel VT or AMD-V) are required for full virtualization.
  1. Run the following command to verify the CPU virtualization extensions are available:
    $ grep -E 'svm|vmx' /proc/cpuinfo
    
  2. Analyze the output.
    • The following output contains a vmx entry indicating an Intel processor with the Intel VT extensions:
      flags   : fpu tsc msr pae mce cx8 apic mtrr mca cmov pat pse36 clflush 
      	dts acpi mmx fxsr sse sse2 ss ht  tm syscall lm constant_tsc pni monitor ds_cpl
      	vmx est tm2 cx16 xtpr lahf_lm
      
    • The following output contains an svm entry indicating an AMD processor with the AMD-V extensions:
      flags   :  fpu tsc msr pae mce cx8 apic mtrr mca cmov pat pse36 clflush
      	mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt lm 3dnowext 3dnow pni cx16
      	lahf_lm cmp_legacy svm cr8legacy ts fid vid ttp tm stc
      
    If any output is received, the processor has the hardware virtualization extensions. However in some circumstances manufacturers disable the virtualization extensions in BIOS.
    The "flags:" output content may appear multiple times, once for each hyperthread, core or CPU on the system.
    The virtualization extensions may be disabled in the BIOS. If the extensions do not appear or full virtualization does not work refer to Procedure 34.1, “Enabling virtualization extensions in BIOS”.
  3. For users of the KVM hypervisor

    If the kvm package is installed. I As an additional check, verify that the kvm modules are loaded in the kernel:
    # lsmod | grep kvm
    
    If the output includes kvm_intel or kvm_amd then the kvm hardware virtualization modules are loaded and your system meets requirements. sudo

Additional output

If the libvirt package is installed, the virsh command can output a full list of virtualization system capabilities. Run virsh capabilities as root to receive the complete list.

24.4. Setting KVM processor affinities

This section covers setting processor and processing core affinities with libvirt and KVM guests.
By default, libvirt provisions guests using the hypervisor's default policy. For most hypervisors, the policy is to run guests on any available processing core or CPU. There are times when an explicit policy may be better, in particular for systems with a NUMA (Non-Uniform Memory Access) architecture. A guest on a NUMA system should be pinned to a processing core so that its memory allocations are always local to the node it is running on. This avoids cross-node memory transports which have less bandwidth and can significantly degrade performance.
On a non-NUMA systems some form of explicit placement across the hosts’ sockets, cores and hyperthreads may be more efficient.
Identifying CPU and NUMA topology
The first step in deciding what policy to apply is to determine the host’s memory and CPU topology. The virsh nodeinfo command provides information about how many sockets, cores and hyperthreads there are attached a host.
# virsh nodeinfo
CPU model:           x86_64
CPU(s):              8
CPU frequency:       1000 MHz
CPU socket(s):       2
Core(s) per socket:  4
Thread(s) per core:  1
NUMA cell(s):        1
Memory size:         8179176 kB
This system has eight CPUs, in two sockets, each processor has four cores.
The output shows that that the system has a NUMA architecture. NUMA is more complex and requires more data to accurately interpret. Use the virsh capabilities to get additional output data on the CPU configuration.
# virsh capabilities
<capabilities>
  <host>
    <cpu>
      <arch>x86_64</arch>
    </cpu>
    <migration_features>
      <live/>
      <uri_transports>
        <uri_transport>tcp</uri_transport>
      </uri_transports>
    </migration_features>
    <topology>
      <cells num='2'>
        <cell id='0'>
          <cpus num='4'>
            <cpu id='0'/>
            <cpu id='1'/>
            <cpu id='2'/>
            <cpu id='3'/>
          </cpus>
        </cell>
        <cell id='1'>
          <cpus num='4'>
            <cpu id='4'/>
            <cpu id='5'/>
            <cpu id='6'/>
            <cpu id='7'/>
          </cpus>
        </cell>
      </cells>
    </topology>
    <secmodel>
      <model>selinux</model>
      <doi>0</doi>
    </secmodel>
  </host>

 [ Additional XML removed ]

</capabilities>
The output shows two NUMA nodes (also know as NUMA cells), each containing four logical CPUs (four processing cores). This system has two sockets, therefore it can be inferred that each socket is a separate NUMA node. For a guest with four virtual CPUs, it would be optimal to lock the guest to physical CPUs 0 to 3, or 4 to 7 to avoid accessing non-local memory, which are significantly slower than accessing local memory.
If a guest requires eight virtual CPUs, as each NUMA node only has four physical CPUs, a better utilization may be obtained by running a pair of four virtual CPU guests and splitting the work between them, rather than using a single 8 CPU guest. Running across multiple NUMA nodes significantly degrades performance for physical and virtualized tasks.
Decide which NUMA node can run the guest
Locking a guest to a particular NUMA node offers no benefit if that node does not have sufficient free memory for that guest. libvirt stores information on the free memory available on each node. Use the virsh freecell command to display the free memory on all NUMA nodes.
# virsh freecell
0: 2203620 kB
1: 3354784 kB
If a guest requires 3 GB of RAM allocated, then the guest should be run on NUMA node (cell) 1. Node 0 only has 2.2GB free which is probably not sufficient for certain guests.
Lock a guest to a NUMA node or physical CPU set
Once you have determined which node to run the guest on, refer to the capabilities data (the output of the virsh capabilities command) about NUMA topology.
  1. Extract from the virsh capabilities output.
    <topology>
      <cells num='2'>
        <cell id='0'>
        <cpus num='4'>
          <cpu id='0'/>
          <cpu id='1'/>
          <cpu id='2'/>
          <cpu id='3'/>
        </cpus>
      </cell>
      <cell id='1'>
        <cpus num='4'>
          <cpu id='4'/>
          <cpu id='5'/>
          <cpu id='6'/>
          <cpu id='7'/>
        </cpus>
      </cell>
      </cells>
    </topology>
  2. Observe that the node 1, <cell id='1'>, has physical CPUs 4 to 7.
  3. The guest can be locked to a set of CPUs by appending the cpuset attribute to the configuration file.
    1. While the guest is offline, open the configuration file with virsh edit.
    2. Locate where the guest's virtual CPU count is specified. Find the vcpus element.
      <vcpus>4</vcpus>
      The guest in this example has four CPUs.
    3. Add a cpuset attribute with the CPU numbers for the relevant NUMA cell.
      <vcpus cpuset='4-7'>4</vcpus>
  4. Save the configuration file and restart the guest.
The guest has been locked to CPUs 4 to 7.
Automatically locking guests to CPUs with virt-install
The virt-install provisioning tool provides a simple way to automatically apply a 'best fit' NUMA policy when guests are created.
The cpuset option for virt-install can use a CPU set of processors or the parameter auto. The auto parameter automatically determines the optimal CPU locking using the available NUMA data.
For a NUMA system, use the --cpuset=auto with the virt-install command when creating new guests.
Tuning CPU affinity on running guests
There may be times where modifying CPU affinities on running guests is preferable to rebooting the guest. The virsh vcpuinfo and virsh vcpupin commands can perform CPU affinity changes on running guests.
The virsh vcpuinfo command gives up to date information about where each virtual CPU is running.
In this example, guest1 is a guest with four virtual CPUs is running on a KVM host.
# virsh vcpuinfo guest1
VCPU:           0
CPU:            3
State:          running
CPU time:       0.5s
CPU Affinity:   yyyyyyyy
VCPU:           1
CPU:            1
State:          running
CPU Affinity:   yyyyyyyy
VCPU:           2
CPU:            1
State:          running
CPU Affinity:   yyyyyyyy
VCPU:           3
CPU:            2
State:          running
CPU Affinity:   yyyyyyyy
The virsh vcpuinfo output (the yyyyyyyy value of CPU Affinity) shows that the guest can presently run on any CPU.
To lock the virtual CPUs to the second NUMA node (CPUs four to seven), run the following commands.
# virsh vcpupin guest1 0 4
# virsh vcpupin guest1 1 5
# virsh vcpupin guest1 2 6
# virsh vcpupin guest1 3 7
The virsh vcpuinfo command confirms the change in affinity.
# virsh vcpuinfo guest1
VCPU:           0
CPU:            4
State:          running
CPU time:       32.2s
CPU Affinity:   ----y---
VCPU:           1
CPU:            5
State:          running
CPU time:       16.9s
CPU Affinity:   -----y--
VCPU:           2
CPU:            6
State:          running
CPU time:       11.9s
CPU Affinity:   ------y-
VCPU:           3
CPU:            7
State:          running
CPU time:       14.6s
CPU Affinity:   -------y
Information from the KVM processes can also confirm that the guest is now running on the second NUMA node.
# grep pid /var/run/libvirt/qemu/guest1.xml
<domstatus state='running' pid='4907'>
# grep Cpus_allowed_list /proc/4907/task/*/status
/proc/4907/task/4916/status:Cpus_allowed_list: 4
/proc/4907/task/4917/status:Cpus_allowed_list: 5
/proc/4907/task/4918/status:Cpus_allowed_list: 6
/proc/4907/task/4919/status:Cpus_allowed_list: 7
</section>

24.5. Generating a new unique MAC address

In some case you will need to generate a new and unique MAC address for a guest. There is no command line tool available to generate a new MAC address at the time of writing. The script provided below can generate a new MAC address for your guests. Save the script to your guest as macgen.py. Now from that directory you can run the script using ./macgen.py and it will generate a new MAC address. A sample output would look like the following:
$ ./macgen.py 
00:16:3e:20:b0:11
	
#!/usr/bin/python
# macgen.py script to generate a MAC address for virtualized guests
#
import random
#
def randomMAC():
	mac = [ 0x00, 0x16, 0x3e,
		random.randint(0x00, 0x7f),
		random.randint(0x00, 0xff),
		random.randint(0x00, 0xff) ]
	return ':'.join(map(lambda x: "%02x" % x, mac))
#
print randomMAC()
Another method to generate a new MAC for your guest
You can also use the built-in modules of python-virtinst to generate a new MAC address and UUID for use in a guest configuration file:
# echo  'import virtinst.util ; print\
 virtinst.util.uuidToString(virtinst.util.randomUUID())' | python
# echo  'import virtinst.util ; print virtinst.util.randomMAC()' | python
The script above can also be implemented as a script file as seen below.
#!/usr/bin/env python
#  -*- mode: python; -*-
print ""
print "New UUID:"
import virtinst.util ; print virtinst.util.uuidToString(virtinst.util.randomUUID())
print "New MAC:"
import virtinst.util ; print virtinst.util.randomMAC()
print ""

24.6. Improving guest response time

Virtualized guests can sometimes be slow to respond with certain workloads and usage patterns. Examples of situations which may cause slow or unresponsive guests:
  • Severely overcommitted memory.
  • Overcommitted memory with high processor usage
  • Other (not qemu-kvm processes) busy or stalled processes on the host.
These types of workload may cause guests to appear slow or unresponsive. Usually, the guests memory is eventually fully loaded from swap into the hosts main memory. Once the guest is loaded in main memory, the guest will preform normally. Note, the process of loading a guest from swap to main memory may take several seconds per gigabyte of RAM assigned to the guest depending on the type of storage used for swap and the performance of the components.
KVM virtualized guests function as Linux processes. Linux processes are not permanently kept in main memory (physical RAM). The kernel scheduler swaps process memory into virtual memory (swap). Swap, with conventional hard disk drives, is thousands of times slower than main memory in modern computers. If a guest is inactive for long periods of time, the guest may be placed into swap by the kernel.
KVM virtualized guests processes may be moved to swap regardless of whether memory is overcommitted or overall memory usage.
Using unsafe overcommit levels or overcommitting with swap turned off guest processes or other critical processes may be killed by the pdflush kernel function. pdflush automatically kills processes to keep the system from crashing and to free up memory. Always ensure the host has sufficient swap space when overcommitting memory.
For more information on overcommitting with KVM, refer to Chapter 20, Overcommitting with KVM.

Warning: turning off swap

Virtual memory allows Linux system to use more memory than there is physical RAM on the system. Underused processes are swapped out which allows active processes to use memory, improving memory utilization. Disabling swap reduces memory utilization as all processes are stored in physical RAM.
If swap is turned off, do not overcommit guests. Overcommitting guests without any swap can cause guests or the host system to crash.
Turning off swap
Swap usage can be completely turned off to prevent guests from being unresponsive while they are moved back to main memory. This may improve performance but will expose the system to certain risks.
The swapoff command can disable all swap partitions and swap files on a system.
# swapoff -a
To make this change permanent, remove swap lines from the /etc/fstab file and restart the host system.
Using SSDs for swap
Using Solid State Drives (SSDs) for swap storage may improve the performance of virtualized guests.
Using RAID arrays, faster disks or separate drives dedicated to swap may also improve performance.

24.7. Very Secure ftpd

vsftpd can provide access to installation trees for para-virtualized guests (for example, the Red Hat Enterprise Linux repositories) or other data. If you have not installed vsftpd during the server installation you can grab the RPM package from your Server directory of your installation media and install it using the rpm -ivh vsftpd*.rpm (note that the RPM package must be in your current directory).
  1. To configure vsftpd, edit /etc/passwd using vipw and change the ftp user's home directory to the directory where you are going to keep the installation trees for your guests. An example entry for the FTP user would look like the following:
    ftp:x:14:50:FTP User:/installtree/:/sbin/nologin
    
  2. Verify that vsftpd is not enabled using the chkconfig --list vsftpd:
    $ chkconfig --list vsftpd
    vsftpd          0:off   1:off   2:off   3:off   4:off   5:off   6:off
    
  3. Run the chkconfig --levels 345 vsftpd on to start vsftpd automatically for run levels 3, 4 and 5.
  4. Use the chkconfig --list vsftpd command to verify the vsftpd daemon is enabled to start during system boot:
    $ chkconfig --list vsftpd
    vsftpd          0:off   1:off   2:off   3:on    4:on    5:on    6:off
    
  5. use the service vsftpd start vsftpd to start the vsftpd service:
    $service vsftpd start vsftpd
    Starting vsftpd for vsftpd:                  [  OK  ]
    

24.8. Disable SMART disk monitoring for guests

SMART disk monitoring can be safely disabled as virtual disks and the physical storage devices are managed by the host.
# service smartd stop
# chkconfig --del smartd

24.9. Configuring a VNC Server

To configure a VNC server use the Remote Desktop application in System > Preferences. Alternatively, you can run the vino-preferences command.
The following steps set up a dedicated VNC server session:
  1. Edit the ~/.vnc/xstartup file to start a GNOME session whenever vncserver is started. The first time you run the vncserver script it will ask you for a password you want to use for your VNC session.
  2. A sample xstartup file:
    #!/bin/sh
    # Uncomment the following two lines for normal desktop:
    # unset SESSION_MANAGER
    # exec /etc/X11/xinit/xinitrc
    [ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
    [ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
    #xsetroot -solid grey
    #vncconfig -iconic &
    #xterm -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &
    #twm &
    if test -z "$DBUS_SESSION_BUS_ADDRESS" ; then
    	eval `dbus-launch --sh-syntax –exit-with-session`
    	echo "D-BUS per-session daemon address is: \
    	$DBUS_SESSION_BUS_ADDRESS"
    fi
    exec  gnome-session
    

24.10. Gracefully shutting down guests

Installing virtualized Red Hat Enterprise Linux 6 guests with the Minimal installation installation option will not install the acpid package.
Without the acpid package, the Red Hat Enterprise Linux 6 guest does not shut down when the virsh shutdown command is executed. The virsh shutdown command is designed to gracefully shut down virtualized guests.
Using virsh shutdown is easier and safer for system administration. Without graceful shut down with the virsh shutdown command a system administrator must log into a virtualized guest manually or send the Ctrl-Alt-Del key combination to each guest.

Other virtualized operating systems

Other virtualized operating systems may be affected by this issue. The virsh shutdown command requires that the guest operating system is configured to handle ACPI shut down requests. Many operating systems require additional configuration on the guest operating system to accept ACPI shut down requests.
Procedure 24.1. Workaround for Red Hat Enterprise Linux 6
  1. Install the acpid package

    The acpid service listen and processes ACPI requests.
    Log into the guest and install the acpid package on the guest:
    # yum install acpid
  2. Enable the acpid service

    Set the acpid service to start during the guest boot sequence and start the service:
    # chkconfig acpid on
    # service acpid start
The guest is now configured to shut down when the virsh shutdown command is used.

24.11. Virtual machine timer management with libvirt

Accurate time keeping on virtualized guests is a key challenge for virtualization platforms. Different hypervisors attempt to handle the problem of time keeping in a variety of ways. Libvirt provides hypervisor independent configuration settings for time management, using the <clock> and <timer> elements in the domain XML. Note that not all options are supported for all hypervisors. The domain XML can be edited using the virsh edit command. See Editing a guest's configuration file for details.
<clock>
The clock element is used to determine how the guest clock is synchronized with the host clock. The clock element has the following attributes:
  • offset
    Determines how the guest clock is offset from the host clock. The offset attribute has the following possible values:
    Table 24.1. Offset attribute values
    Value Description
    utc The guest clock will be synchronized to UTC when booted.
    localtime The guest clock will be synchronized to the host's configured timezone when booted, if any.
    timezone The guest clock will be synchronized to a given timezone, specified by the timezone attribute.
    variable The guest clock will be synchronized to an arbitrary offset from UTC. The delta relative to UTC is specified in seconds, using the adjustment attribute. The guest is free to adjust the Real Time Clock (RTC) over time and expect that it will be honored following the next reboot. This is in contrast to utc mode, where any RTC adjustments are lost at each reboot.

  • timezone
    The timezone to which the guest clock is to be synchronized.
  • adjustment
    The delta for guest clock synchronization. In seconds, relative to UTC.
Example 24.1. Always synchronize to UTC
<clock offset="utc" />

Example 24.2. Always synchronize to the host timezone
<clock offset="localtime" />

Example 24.3. Synchronize to an arbitrary timezone
<clock offset="timezone" timezone="Europe/Paris" />

Example 24.4. Synchronize to UTC + arbitrary offset
<clock offset="variable" adjustment="123456" />

<timer>
A clock element can have zero or more timer elements as children. The timer element specifies a time source used for guest clock synchronization. The timer element has the following attributes. Only the name is required, all other attributes are optional.
  • name
    The name of the time source to use.
    Table 24.2. name attribute values
    Value Description
    platform The master virtual time source which may be used to drive the policy of other time sources.
    pit Programmable Interval Timer - a timer with periodic interrupts.
    rtc Real Time Clock - a continuously running timer with periodic interrupts.
    hpet High Precision Event Timer - multiple timers with periodic interrupts.
    tsc Time Stamp Counter - counts the number of ticks since reset, no interrupts.

  • wallclock
    Specifies whether the wallclock should track host or guest time. Only valid for a name value of platform or rtc.
    Table 24.3. wallclock attribute values
    Value Description
    host RTC wallclock always tracks host time.
    guest RTC wallclock always tracks guest time.

  • tickpolicy
    The policy used to pass ticks on to the guest.
    Table 24.4. tickpolicy attribute values
    Value Description
    none Continue to deliver at normal rate (i.e. ticks are delayed).
    catchup Deliver at a higher rate to catch up.
    merge Ticks merged into one single tick.
    discard All missed ticks are discarded.

  • frequency
    Used to set a fixed frequency, measured in Hz. This attribute is only relevant for a name value of tsc. All other timers operate at a fixed frequency (pit, rtc), or at a frequency fully controlled by the guest (hpet).
  • mode
    Determines how the time source is exposed to the guest. This attribute is only relevant for a name value of tsc. All other timers are always emulated.
    Table 24.5. mode attribute values
    Value Description
    auto Native if safe, otherwise emulated.
    native Always native.
    emulate Always emulate.
    paravirt Native + para-virtualized.

  • present
    Used to override the default set of timers visible to the guest. For example, to enable or disable the HPET.
    Table 24.6. present attribute values
    Value Description
    yes Force this timer to the visible to the guest.
    no Force this timer to not be visible to the guest.

Example 24.5. Clock synchronizing to local time with RTC and PIT timers, and the HPET timer disabled
<clock mode="localtime">
	<timer name="rtc" tickpolicy="catchup" wallclock="guest" />
	<timer name="pit" tickpolicy="none" />
	<timer name="hpet" present="no" />
</clock>

Part V. Virtualization storage topics

Chapter 25. Storage concepts

This chapter introduces the concepts used for describing managing storage devices.
Local storage
Local storage is directly attached to the host server. Local storage includes local directories, directly attached disks, and LVM volume groups on local storage devices.
Networked storage
Networked storage covers storage devices shared over a network using standard protocols. Networked storage includes shared storage devices using Fibre Channel, iSCSI, NFS, GFS2, and SCSI RDMA protocols. Networked storage is a requirement for migrating guest virtualized guests between hosts.

25.1. Storage pools

A storage pool is a file, directory, or storage device managed by libvirt for the purpose of providing storage to virtualized guests. Storage pools are divided into storage volumes that store virtualized guest images or are attached to virtualized guests as additional storage.
libvirt uses a directory-based storage pool, the /var/lib/libvirt/images/ directory, as the default storage pool. The default storage pool can be changed to another storage pool.
Storage pools can be divided up into volumes or allocated directly to a guest. Volumes of a storage pool can be allocated to virtualized guests. There are two categories of storage pool available:
Local storage pools
Local storage pools are directly attached to the host server. Local storage pools include local directories, directly attached disks, and LVM volume groups on local devices.
Local storage pools are useful for development, testing and small deployments that do not require migration or large numbers of virtualized guests. Local storage pools are not suitable for many production environments as local storage pools do not support live migration.
Networked (shared) storage pools
Networked storage pools covers storage devices shared over a network using standard protocols.
Supported protocols for networked storage pools:
  • Fibre Channel-based LUNs
  • iSCSI
  • NFS
  • GFS2
  • SCSI RDMA protocols (SCSI RCP), the block export protocol used in Infiniband and 10GbE iWARP adapters.
Networked storage is a requirement for migrating guest virtualized guests between hosts. Networked storage pools are managed by libvirt.

25.2.  Volumes

Storage pools are divided into storage volumes. Storage volumes are an abstraction of physical partitions, LVM logical volumes, file-based disk images and other storage types handled by libvirt. Storage volumes are presented to virtualized guests as local storage devices regardless of the underlying hardware.
Referencing volumes
To reference a specific volume, three approaches are possible:
The name of the volume and the storage pool
A volume may be referred to by name, along with an identifier for the storage pool it belongs in. On the virsh command line, this takes the form --pool storage_pool volume_name.
For example, a volume named firstimage in the guest_images pool.
# virsh vol-info --pool guest_images
						firstimage
Name:           firstimage
Type:           block
Capacity:       20.00 GB
Allocation:     20.00 GB

virsh #
The full path to the storage on the host system
A volume may also be referred to by its full path on the file system. When using this approach, a pool identifier does not need to be included.
For example, a volume named secondimage.img, visible to the host system as /images/secondimage.img. The image can be referred to as /images/secondimage.img.
# virsh vol-info /images/secondimage.img
Name:           secondimage.img
Type:           file
Capacity:       20.00 GB
Allocation:     136.00 KB
The unique volume key
When a volume is first created in the virtualization system, a unique identifier is generated and assigned to it. The unique identifier is termed the volume key. The format of this volume key varies upon the storage used.
When used with block based storage such as LVM, the volume key may follow this format:
c3pKz4-qPVc-Xf7M-7WNM-WJc8-qSiz-mtvpGn
When used with file based storage, the volume key may instead be a copy of the full path to the volume storage.
/images/secondimage.img
For example, a volume with the volume key of Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr:
# virsh vol-info Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr
Name:           firstimage
Type:           block
Capacity:       20.00 GB
Allocation:     20.00 GB
virsh provides commands for converting between a volume name, volume path, or volume key:
vol-name
Returns the volume name when provided with a volume path or volume key.
# virsh vol-name /dev/guest_images/firstimage firstimage
# virsh vol-name Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr
vol-path
Returns the volume path when provided with a volume key, or a storage pool identifier and volume name.
# virsh vol-path Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr
/dev/guest_images/firstimage
# virsh vol-path --pool guest_images firstimage
/dev/guest_images/firstimage
The vol-key command
Returns the volume key when provided with a volume path, or a storage pool identifier and volume name.
# virsh vol-key /dev/guest_images/firstimage
Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr
# virsh vol-key --pool guest_images firstimage Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr

Chapter 26.  Storage pools

26.1.  Creating storage pools

26.1.1. Dedicated storage device-based storage pools

This section covers dedicating storage devices to virtualized guests.

Security issues with dedicated disks

Guests should not be given write access to whole disks or block devices (for example, /dev/sdb). Use partitions (for example, /dev/sdb1) or LVM volumes.
Guests with full access to a disk device may be able to maliciously access other disk devices that they are not assigned due to disks not having access control lists.

26.1.1.1. Creating a dedicated disk storage pool using virsh

This procedure creates a new storage pool using a dedicated disk device with the virsh command.

Warning

Dedicating a disk to a storage pool will reformat and erase all data presently stored on the disk device. Back up the storage device before commencing the procedure.
  1. Create a GPT disk label on the disk

    The disk must be relabeled with a GUID Partition Table (GPT) disk label. GPT disk labels allow for creating a large numbers of partitions, up to 128 partitions, on each device. GPT partition tables can store partition data for far more partitions than the msdos partition table.
    # parted /dev/sdb
    GNU Parted 2.1
    Using /dev/sdb
    Welcome to GNU Parted! Type 'help' to view a list of commands.
    (parted) mklabel                                                          
    New disk label type? gpt                                                  
    (parted) quit                                                             
    Information: You may need to update /etc/fstab.                           
    
    #
    
  2. Create the storage pool configuration file

    Create a temporary XML text file containing the storage pool information required for the new device.
    The file must be in the format shown below, and contain the following fields:
    <name>guest_images_disk</name>
    The name parameter determines the name of the storage pool. This example uses the name guest_images_disk in the example below.
    <device path='/dev/sdb'/>
    The device parameter with the path attribute specifies the device path of the storage device. This example uses the device /dev/sdb .
    <target> <path>/dev</path>
    The file system target parameter with the path sub-parameter determines the location on the host file system to attach volumes created with this this storage pool.
    For example, sdb1, sdb2, sdb3. Using /dev/, as in the example below, means volumes created from this storage pool can be accessed as /dev/sdb1, /dev/sdb2, /dev/sdb3.
    <format type='gpt'/>
    The format parameter specifies the partition table type. his example uses the gpt in the example below, to match the GPT disk label type created in the previous step.
    Create the XML file for the storage pool device with a text editor.
    Example 26.1. Dedicated storage device storage pool
    <pool type='disk'>
      <name>guest_images_disk</name>
      <source>
        <device path='/dev/sdb'/>
        <format type='gpt'/>
      </source>
      <target>
        <path>/dev</path>
      </target>
      </pool>
    

  3. Attach the device

    Add the storage pool definition using the virsh pool-define command with the XML configuration file created in the previous step.
    # virsh pool-define ~/guest_images_disk.xml
    Pool guest_images_disk defined from /root/guest_images_disk.xml
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    guest_images_disk    inactive   no
    
  4. Start the storage pool

    Start the storage pool with the virsh pool-start command. Verify the pool is started with the virsh pool-list --all command.
    # virsh pool-start guest_images_disk
    Pool guest_images_disk started
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    guest_images_disk    active     no
    
  5. Turn on autostart

    Turn on autostart for the storage pool. Autostart configures the libvirtd service to start the storage pool when the service starts.
    # virsh pool-autostart guest_images_disk
    Pool guest_images_disk marked as autostarted
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    guest_images_disk    active     yes
    
  6. Verify the storage pool configuration

    Verify the storage pool was created correctly, the sizes reported correctly, and the state reports as running.
    # virsh pool-info guest_images_disk
    Name:           guest_images_disk
    UUID:           551a67c8-5f2a-012c-3844-df29b167431c
    State:          running
    Capacity:       465.76 GB
    Allocation:     0.00 
    Available:      465.76 GB
    # ls -la /dev/sdb
    brw-rw----. 1 root disk 8, 16 May 30 14:08 /dev/sdb
    # virsh vol-list guest_images_disk
    Name                 Path
    -----------------------------------------
    
  7. Optional: Remove the temporary configuration file

    Remove the temporary storage pool XML configuration file if it is not needed.
    # rm ~/guest_images_disk.xml
    
    
A dedicated storage device storage pool is now available.

26.1.2. Partition-based storage pools

This section covers using a pre-formatted block device, a partition, as a storage pool.
For the following examples, a host has a 500GB hard drive (/dev/sdc) partitioned into one 500GB, ext4 formatted partition (/dev/sdc1). We set up a storage pool for it using the procedure below.

26.1.2.1. Creating a partition-based storage pool using virt-manager

This procedure creates a new storage pool using a partition of a storage device.
Procedure 26.1. Creating a partition-based storage pool with virt-manager
  1. Open the storage pool settings

    1. In the virt-manager graphical interface, select the host from the main window.
      Open the Edit menu and select Host Details
    2. Click on the Storage tab of the Host Details window.
  2. Create the new storage pool

    1. Add a new pool (part 1)

      Press the + button (the add pool button). The Add a New Storage Pool wizard appears.
      Choose a Name for the storage pool. This example uses the name guest_images_fs. Change the Type to fs: Pre-Formatted Block Device.
      Press the Forward button to continue.
    2. Add a new pool (part 2)

      Change the Target Path, Format, and Source Path fields.
      Target Path
      Enter the location to mount the source device for the storage pool in the Target Path field. If the location does does not already exist, virt-manager will create the directory.
      Format
      Select a format from the Format list. The device is formatted with the selected format.
      This example uses the ext4 file system, the default Red Hat Enterprise Linux file system.
      Source Path
      Enter the device in the Source Path field.
      This example uses the /dev/sdc1 device.
      Verify the details and press the Finish button to create the storage pool.
  3. Verify the new storage pool

    The new storage pool appears in the storage list on the left after a few seconds. Verify the size is reported as expected, 458.20 GB Free in this example. Verify the State field reports the new storage pool as Active.
    Select the storage pool. In the Autostart field, click the On Boot checkbox. This will make sure the storage device starts whenever the libvirtd service starts.
    The storage pool is now created, close the Host Details window.

26.1.2.2. Creating a partition-based storage pool using virsh

This section covers creating a partition-based storage pool with the virsh command.

Security warning

Do not use this procedure to assign an entire disk as a storage pool (for example, /dev/sdb). Guests should not be given write access to whole disks or block devices. Only use this method to assign partitions (for example, /dev/sdb1) to storage pools.
Procedure 26.2. Creating pre-formatted block device storage pools using virsh
  1. Create the storage pool definition

    Use the virsh pool-define-as command to create a new storage pool definition. There are three options that must be provided to define a pre-formatted disk as a storage pool:
    Partition name
    The name parameter determines the name of the storage pool. This example uses the name guest_images_fs in the example below.
    device
    The device parameter with the path attribute specifies the device path of the storage device. This example uses the partition /dev/sdc1 .
    mountpoint
    The mountpoint on the local file system where the formatted device will be mounted. If the mount point directory does not exist, the virsh command can create the directory.
    The directory /guest_images is used in this example.
    # virsh pool-define-as guest_images_fs fs - - /dev/sdc1 - "/guest_images"
    Pool guest_images_fs defined
    
    The new pool and mount points are now created.
  2. Verify the new pool

    List the present storage pools.
    # virsh pool-list --all
    Name                 State      Autostart
    -----------------------------------------
    default              active     yes
    guest_images_fs      inactive   no
    
  3. Ceate the mount point

    Use the virsh pool-build command to create a mount point for a pre-formatted file system storage pool.
    # virsh pool-build guest_images_fs
    Pool guest_images_fs built
    # ls -la /guest_images
    total 8
    drwx------.  2 root root 4096 May 31 19:38 .
    dr-xr-xr-x. 25 root root 4096 May 31 19:38 ..
    # virsh pool-list --all
    Name                 State      Autostart
    -----------------------------------------
    default              active     yes
    guest_images_fs      inactive   no
    
    
  4. Start the storage pool

    Use the virsh pool-start command to mount the file system onto the mount point and make the pool available for use.
    # virsh pool-start guest_images_fs
    Pool guest_images_fs started
    # virsh pool-list --all
    Name                 State      Autostart
    -----------------------------------------
    default              active     yes
    guest_images_fs      active     no
    
  5. Turn on autostart

    By default, a storage pool is defined with virsh is not set to automatically start each time the libvirtd starts. Turn on automatic start with the virsh pool-autostart command. The storage pool is now automatically started each time libvirtd starts.
    # virsh pool-autostart guest_images_fs
    Pool guest_images_fs marked as autostarted
    
    # virsh pool-list --all
    Name                 State      Autostart
    -----------------------------------------
    default              active     yes
    guest_images_fs      active     yes
    
  6. Verify the storage pool

    Verify the storage pool was created correctly, the sizes reported are as expected, and the state is reported as running. Verify there is a "lost+found" directory in the mount point on the file system, indicating the device is mounted.
    # virsh pool-info guest_images_fs
    Name:           guest_images_fs
    UUID:           c7466869-e82a-a66c-2187-dc9d6f0877d0
    State:          running
    Capacity:       458.39 GB
    Allocation:     197.91 MB
    Available:      458.20 GB
    # mount | grep /guest_images
    /dev/sdc1 on /guest_images type ext4 (rw)
    # ls -la /guest_images
    total 24
    drwxr-xr-x.  3 root root  4096 May 31 19:47 .
    dr-xr-xr-x. 25 root root  4096 May 31 19:38 ..
    drwx------.  2 root root 16384 May 31 14:18 lost+found
    

26.1.3. Directory-based storage pools

This section covers storing virtualized guests in a directory on the host.
Directory-based storage pools can be created with virt-manager or the virsh command line tools.

26.1.3.1. Creating a directory-based storage pool with virt-manager

  1. Create the local directory

    1. Optional: Create a new directory for the storage pool

      Create the directory on the host for the storage pool. An existing directory can be used if permissions and SELinux are configured correctly. This example uses a directory named /guest_images.
      # mkdir /guest_images
    2. Set directory ownership

      Change the user and group ownership of the directory. The directory must be owned by the root user.
      # chown root:root /guest_images
    3. Set directory permissions

      Change the file permissions of the directory.
      # chmod 700 /guest_images
    4. Verify the changes

      Verify the permissions were modified. The output shows a correctly configured empty directory.
      # ls -la /guest_images
      total 8
      drwx------.  2 root root 4096 May 28 13:57 .
      dr-xr-xr-x. 26 root root 4096 May 28 13:57 ..
      
  2. Configure SELinux file contexts

    Configure the correct SELinux context for the new directory.
    # semanage fcontext -a -t virt_image_t /guest_images
    
  3. Open the storage pool settings

    1. In the virt-manager graphical interface, select the host from the main window.
      Open the Edit menu and select Host Details
    2. Click on the Storage tab of the Host Details window.
  4. Create the new storage pool

    1. Add a new pool (part 1)

      Press the + button (the add pool button). The Add a New Storage Pool wizard appears.
      Choose a Name for the storage pool. This example uses the name guest_images_dir. Change the Type to dir: Filesystem Directory.
      Press the Forward button to continue.
    2. Add a new pool (part 2)

      Change the Target Path field. This example uses /guest_images.
      Verify the details and press the Finish button to create the storage pool.
  5. Verify the new storage pool

    The new storage pool appears in the storage list on the left after a few seconds. Verify the size is reported as expected, 36.41 GB Free in this example. Verify the State field reports the new storage pool as Active.
    Select the storage pool. In the Autostart field, click the On Boot checkbox. This will make sure the storage pool starts whenever the libvirtd service sarts.
    The storage pool is now created, close the Host Details window.

26.1.3.2. Creating a directory-based storage pool with virsh

  1. Create the storage pool definition

    Use the virsh pool-define-as command to define a new storage pool. There are two options required for creating directory-based storage pools:
    • The name of the storage pool.
      This example uses the name guest_images_dir. All further virsh commands used in this example use this name.
    • The path to a file system directory for storing virtualized guest image files . If this directory does not exist, virsh will create it.
      This example uses the /guest_images directory.
     # virsh pool-define-as guest_images_dir dir - - - - "/guest_images"
    Pool guest_images_dir defined
  2. Verify the storage pool is listed

    Verify the storage pool object is created correctly and the state reports it as inactive.
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    guest_images_dir     inactive   no
  3. Create the local directory

    Use the virsh pool-build command to build the directory-based storage pool. virsh pool-build sets the required permissions and SELinux settings for the directory and creates the directory if it does not exist.
    # virsh pool-build guest_images_dir
    Pool guest_images_dir built
    # ls -la /guest_images
    total 8
    drwx------.  2 root root 4096 May 30 02:44 .
    dr-xr-xr-x. 26 root root 4096 May 30 02:44 ..
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    guest_images_dir     inactive   no
  4. Start the storage pool

    Use the virsh command pool-start for this. pool-start enables a directory storage pool, allowing it to be used for volumes and guests.
    # virsh pool-start guest_images_dir
    Pool guest_images_dir started
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    guest_images_dir    active     no
    
  5. Turn on autostart

    Turn on autostart for the storage pool. Autostart configures the libvirtd service to start the storage pool when the service starts.
    # virsh pool-autostart guest_images_dir
    Pool guest_images_dir marked as autostarted
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    guest_images_dir     active     yes
    
  6. Verify the storage pool configuration

    Verify the storage pool was created correctly, the sizes reported correctly, and the state reports as running.
    # virsh pool-info guest_images_dir
    Name:           guest_images_dir
    UUID:           779081bf-7a82-107b-2874-a19a9c51d24c
    State:          running
    Capacity:       49.22 GB
    Allocation:     12.80 GB
    Available:      36.41 GB
    
    # ls -la /guest_images
    total 8
    drwx------.  2 root root 4096 May 30 02:44 .
    dr-xr-xr-x. 26 root root 4096 May 30 02:44 ..
    #
    
A directory-based storage pool is now available.

26.1.4. LVM-based storage pools

This chapter covers using LVM volume groups as storage pools.
LVM-based storage groups provide flexibility of

Warning

LVM-based storage pools require a full disk partition. This partition will be formatted and all data presently stored on the disk device will be erased. Back up the storage device before commencing the procedure.

26.1.4.1. Creating an LVM-based storage pool with virt-manager

LVM-based storage pools can use existing LVM volume groups or create new LVM volume groups on a blank partition.
  1. Optional: Create new partition for LVM volumes

    These steps describe how to create a new partition and LVM volume group on a new hard disk drive.

    Warning

    This procedure will remove all data from the selected storage device.
    1. Create a new partition

      Use the fdisk command to create a new disk partition from the command line. The following example creates a new partition that uses the entire disk on the storage device /dev/sdb.
      # fdisk /dev/sdb
      Command (m for help):
      
      Press n for a new partition.
    2. Press p for a primary partition.
      Command action
         e   extended
         p   primary partition (1-4)
      
    3. Choose an available partition number. In this example the first partition is chosen by entering 1.
      Partition number (1-4): 1
    4. Enter the default first cylinder by pressing Enter.
      First cylinder (1-400, default 1):
      
    5. Select the size of the partition. In this example the entire disk is allocated by pressing Enter.
      Last cylinder or +size or +sizeM or +sizeK (2-400, default 400):
      
    6. Set the type of partition by pressing t.
      Command (m for help): t
    7. Choose the partition you created in the previous steps. In this example, the partition number is 1.
      Partition number (1-4): 1
    8. Enter 8e for a Linux LVM partition.
      Hex code (type L to list codes): 8e
    9. write changes to disk and quit.
      Command (m for help): w 
      Command (m for help): q
    10. Create a new LVM volume group

      Create a new LVM volume group with the vgcreate command. This example creates a volume group named guest_images_lvm.
      # vgcreate guest_images_lvm /dev/sdb1
        Physical volmue "/dev/vdb1" successfully created
        Volume group "guest_images_lvm" successfully created
      
    The new LVM volume group, guest_images_lvm, can now be used for an LVM-based storage pool.
  2. Open the storage pool settings

    1. In the virt-manager graphical interface, select the host from the main window.
      Open the Edit menu and select Host Details
    2. Click on the Storage tab of the Host Details window.
  3. Create the new storage pool

    1. Start the Wizard

      Press the + button (the add pool button). The Add a New Storage Pool wizard appears.
      Choose a Name for the storage pool. We use guest_images_lvm for this example. Then change the Type to logical: LVM Volume Group, and
      Press the Forward button to continue.
    2. Add a new pool (part 2)

      Change the Target Path field. This example uses /guest_images.
      Now fill in the Target Path and Source Path fields, then tick the Build Pool check box.
      • Use the Target Path field to either select an existing LVM volume group or as the name for a new volume group. The default format is /dev/storage_pool_name.
        This example uses a new volume group named /dev/guest_images_lvm.
      • The Source Path field is optional if an existing LVM volume group is used in the Target Path.
        For new LVM volume groups, input the location of a storage device in the Source Path field. This example uses a blank partition /dev/sdc.
      • The Build Pool checkbox instructs virt-manager to create a new LVM volume group. If you are using an existing volume group you should not select the Build Pool checkbox.
        This example is using a blank partition to create a new volume group so the Build Pool checkbox must be selected.
      Verify the details and press the Finish button format the LVM volume group and create the storage pool.
    3. Confirm the device to be formatted

      A warning message appears.
      Press the Yes button to proceed to erase all data on the storage device and create the storage pool.
  4. Verify the new storage pool

    The new storage pool will appear in the list on the left after a few seconds. Verify the details are what you expect, 465.76 GB Free in our example. Also verify the State field reports the new storage pool as Active.
    It is generally a good idea to have the Autostart check box enabled, to ensure the storage pool starts automatically with libvirtd.
    Close the Host Details dialog, as the task is now complete.

26.1.4.2. Creating an LVM-based storage pool with virsh

  • # virsh pool-define-as guest_images_lvm logical - - /dev/sdc libvirt_lvm /dev/libvirt_lvm
    Pool guest_images_lvm defined
    # virsh pool-build guest_images_lvm
    Pool guest_images_lvm built
    # virsh pool-start guest_images_lvm
    Pool guest_images_lvm started
    # vgs
    VG          #PV #LV #SN Attr   VSize   VFree  
    libvirt_lvm   1   0   0 wz--n- 465.76g 465.76g
    # virsh pool-autostart guest_images_lvm
    Pool guest_images_lvm marked as autostarted
    
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    guest_images_lvm     active     yes       
    
    # virsh vol-create-as guest_images_lvm volume1 8G
    Vol volume1 created
    
    # virsh vol-create-as guest_images_lvm volume2 8G
    Vol volume2 created
    
    # virsh vol-create-as guest_images_lvm volume3 8G
    Vol volume3 created
    
    # virsh vol-list guest_images_lvm
    Name                 Path
    -----------------------------------------
    volume1              /dev/libvirt_lvm/volume1
    volume2              /dev/libvirt_lvm/volume2
    volume3              /dev/libvirt_lvm/volume3
    
    # lvscan
    ACTIVE            '/dev/libvirt_lvm/volume1' [8.00 GiB] inherit
    ACTIVE            '/dev/libvirt_lvm/volume2' [8.00 GiB] inherit
    ACTIVE            '/dev/libvirt_lvm/volume3' [8.00 GiB] inherit
    # lvs
    LV      VG          Attr   LSize   Origin Snap%  Move Log Copy%  Convert
    volume1 libvirt_lvm -wi-a-   8.00g
    volume2 libvirt_lvm -wi-a-   8.00g
    volume3 libvirt_lvm -wi-a-   8.00g
    # vgs
    VG          #PV #LV #SN Attr   VSize   VFree
    libvirt_lvm   1   3   0 wz--n- 465.76g 441.76g
    vg_host2      1   3   0 wz--n- 465.27g      0
    #
    

26.1.5. iSCSI-based storage pools

This section covers using iSCSI-based devices to store virtualized guests.
iSCSI (Internet Small Computer System Interface) is a network protocol for sharing storage devices. iSCSI connects initiators (storage clients) to targets (storage servers) using SCSI instructions over the IP layer. For more information and background on the iSCSI protocol refer to wikipedia's iSCSI article.

26.1.5.1. Configuring a software iSCSI target

The scsi-target-utils package provides a tool for creating software-backed iSCSI targets.
Procedure 26.3. Creating an iSCSI target
  1. Install the required packages

    Install the scsi-target-utils package and all dependencies
    # yum install scsi-target-utils
  2. Start the tgtd service

    The tgtd service hosts SCSI targets and uses the iSCSI protocol to host targets. Start the tgtd service and make the service persistent after restarting with the chkconfig command.
    # service tgtd start
    # chkconfig tgtd on
  3. Optional: Create LVM volumes

    LVM volumes are useful for iSCSI backing images. LVM snapshots and resizing can be beneficial for virtualized guests. This example creates an LVM image named virtimage1 on a new volume group named virtstore on a RAID5 array for hosting virtualized guests with iSCSI.
    1. Create the RAID array

      Creating software RAID5 arrays is covered by the Red Hat Enterprise Linux Deployment Guide.
    2. Create the LVM volume group

      Create a volume group named virtstore with the vgcreate command.
      # vgcreate virtstore /dev/md1
    3. Create a LVM logical volume

      Create a logical volume group named virtimage1 on the virtstore volume group with a size of 20GB using the lvcreate command.
      # lvcreate --size 20G -n virtimage1
      							virtstore
      The new logical volume, virtimage1, is ready to use for iSCSI.
  4. Optional: Create file-based images

    File-based storage is sufficient for testing but is not recommended for production environments or any significant I/O activity. This optional procedure creates a file based imaged named virtimage2.img for an iSCSI target.
    1. Create a new directory for the image

      Create a new directory to store the image. The directory must have the correct SELinux contexts.
      # mkdir -p /var/lib/tgtd/virtualization
    2. Create the image file

      Create an image named virtimage2.img with a size of 10GB.
      # dd if=/dev/zero of=/var/lib/tgtd/virtualization/virtimage2.img bs=1M seek=10000 count=0
    3. Configure SELinux file contexts

      Configure the correct SELinux context for the new image and directory.
      # restorecon -R /var/lib/tgtd
      The new file-based image, virtimage2.img, is ready to use for iSCSI.
  5. Create targets

    Targets can be created by adding a XML entry to the /etc/tgt/targets.conf file. The target attribute requires an iSCSI Qualified Name (IQN). The IQN is in the format:
    iqn.yyyy-mm.reversed domain name:optional identifier text
    Where:
    • yyyy-mm represents the year and month the device was started (for example: 2010-05);
    • reversed domain name is the hosts domain name in reverse (for example server1.example.com in an IQN would be com.example.server1); and
    • optional identifier text is any text string, without spaces, that assists the administrator in identifying devices or hardware.
    This example creates iSCSI targets for the two types of images created in the optional steps on server1.example.com with an optional identifier trial. Add the following to the /etc/tgt/targets.conf file.
    <target iqn.2010-05.com.example.server1:trial>
    backing-store /dev/virtstore/virtimage1  #LUN 1
    backing-store /var/lib/tgtd/virtualization/virtimage2.img  #LUN 2
    write-cache off
    </target>
    Ensure that the /etc/tgt/targets.conf file contains the default-driver iscsi line to set the driver type as iSCSI. The driver uses iSCSI by default.

    Important

    This example creates a globally accessible target without access control. Refer to the scsi-target-utils for information on implementing secure access.
  6. Restart the tgtd service

    Restart the tgtd service to reload the configuration changes.
    # service tgtd restart
  7. iptables configuration

    Open port 3260 for iSCSI access with iptables.
    # iptables -I INPUT -p tcp -m tcp --dport 3260 -j ACCEPT
    # service iptables save
    # service iptables restart
  8. Verify the new targets

    View the new targets to ensure the setup was success with the tgt-admin --show command.
    # tgt-admin --show
    Target 1: iqn.2010-05.com.example.server1:trial
    System information:
    Driver: iscsi
    State: ready
    I_T nexus information:
    LUN information:
    LUN: 0
        Type: controller
        SCSI ID: IET     00010000
        SCSI SN: beaf10
        Size: 0 MB
        Online: Yes
        Removable media: No
        Backing store type: rdwr
        Backing store path: None
    LUN: 1
        Type: disk
        SCSI ID: IET     00010001
        SCSI SN: beaf11
        Size: 20000 MB
        Online: Yes
        Removable media: No
        Backing store type: rdwr
        Backing store path: /dev/virtstore/virtimage1
    LUN: 2
        Type: disk
        SCSI ID: IET     00010002
        SCSI SN: beaf12
        Size: 10000 MB
        Online: Yes
        Removable media: No
        Backing store type: rdwr
        Backing store path: /var/lib/tgtd/virtualization/virtimage2.img
    Account information:
    ACL information:
    ALL

    Security warning

    The ACL list is set to all. This allows all systems on the local network to access this device. It is recommended to set host access ACLs for production environments.
  9. Optional: Test discovery

    Test whether the new iSCSI device is discoverable.
    # iscsiadm --mode discovery --type sendtargets --portal server1.example.com
    127.0.0.1:3260,1 iqn.2010-05.com.example.server1:trial1
  10. Optional: Test attaching the device

    Attach the new device (iqn.2010-05.com.example.server1:trial1) to determine whether the device can be attached.
    # iscsiadm -d2 -m node --login
    scsiadm: Max file limits 1024 1024
    
    Logging in to [iface: default, target: iqn.2010-05.com.example.server1:trial1, portal: 10.0.0.1,3260]
    Login to [iface: default, target: iqn.2010-05.com.example.server1:trial1, portal: 10.0.0.1,3260] successful.
    Detach the device.
    # iscsiadm -d2 -m node --logout
    scsiadm: Max file limits 1024 1024
    
    Logging out of session [sid: 2, target: iqn.2010-05.com.example.server1:trial1, portal: 10.0.0.1,3260
    Logout of [sid: 2, target: iqn.2010-05.com.example.server1:trial1, portal: 10.0.0.1,3260] successful.
An iSCSI device is now ready to use for virtualization.

26.1.5.2. Adding an iSCSI target to virt-manager

This procedure covers creating a storage pool with an iSCSI target in virt-manager.
Procedure 26.4. Adding an iSCSI device to virt-manager
  1. Open the host storage tab

    Open the Storage tab in the Host Details window.
    1. Open virt-manager.
    2. Select a host from the main virt-manager window.
    3. Open the Edit menu and select Host Details.
    4. Click on the Storage tab of the Host Details window.
  2. Add a new pool (part 1)

    Press the + button (the add pool button). The Add a New Storage Pool wizard appears.
    Choose a name for the storage pool, change the Type to iscsi, and press Forward to continue.
  3. Add a new pool (part 2)

    Enter the target path for the device, the host name of the target and the source path (the IQN). The Format option is not available as formatting is handled by the guests. It is not advised to edit the Target Path. The default target path value, /dev/disk/by-path/, adds the drive path to that folder. The target path should be the same on all hosts for migration.
    Enter the hostname or IP address of the iSCSI target. This example uses server1.example.com.
    Enter the source path, the IQN for the iSCSI target. This example uses iqn.2010-05.com.example.server1:trial1.
    Press Finish to create the new storage pool.

26.1.5.3. Creating an iSCSI-based storage pool with virsh

  1. Create the storage pool definition

    The example below is an XML definition file for a iSCSI-based storage pool.
    <name>trial1</name>
    The name element sets the name for the storage pool. The name is required and must be unique.
    <uuid>afcc5367-6770-e151-bcb3-847bc36c5e28</uuid>
    The optional uuid element provides a unique global identifier for the storage pool. The uuid element can contain any valid UUID or an existing UUID for the storage device. If a UUID is not provided, virsh will generate a UUID for the storage pool.
    <host name='server1.example.com'/>
    The host element with the name attribute specifies the hostname of the iSCSI server. The host element attribute can contain a port attribute for a non-standard iSCSI protocol port number.
    <device path='iqn.2010-05.com.example.server1:trial1'/>
    The device element path attribute must contain the IQN for the iSCSI server.
    With a text editor, create an XML file for the iSCSI storage pool. This example uses a XML definition named trial1.xml.
    <pool type='iscsi'>
      <name>trial1</name>
      <uuid>afcc5367-6770-e151-bcb3-847bc36c5e28</uuid>
      <source>
        <host name='server1.example.com'/>
        <device path='iqn.2010-05.com.example.server1:trial1'/>
      </source>
      <target>
        <path>/dev/disk/by-path</path>
       </target>
    </pool>
    Use the pool-define command to define the storage pool but not start it.
    # virsh pool-define trial1.xml
    Pool trial1 defined
    
  2. Alternative step: Use pool-define-as to define the pool from the command line

    Storage pool definitions can be created with the virsh command line tool. Creating storage pools with virsh is useful for systems administrators using scripts to create multiple storage pools.
    The virsh pool-define-as command has several parameters which are accepted in the following format:
    virsh pool-define-as name type source-host source-path source-dev source-name target
    The type, iscsi, defines this pool as an iSCSI based storage pool. The name parameter must be unique and sets the name for the storage pool. The source-host and source-path parameters are the hostname and iSCSI IQN respectively. The source-dev and source-name parameters are not required for iSCSI-based pools, use a - character to leave the field blank. The target parameter defines the location for mounting the iSCSI device on the host.
    The example below creates the same iSCSI-based storage pool as the previous step.
    # virsh pool-define-as trial1 iscsi server1.example.com iqn.2010-05.com.example.server1:trial1 - - /dev/disk/by-path
    Pool trial1 defined
  3. Verify the storage pool is listed

    Verify the storage pool object is created correctly and the state reports as inactive.
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    trial1               inactive   no
  4. Start the storage pool

    Use the virsh command pool-start for this. pool-start enables a directory storage pool, allowing it to be used for volumes and guests.
    # virsh pool-start guest_images_disk
    Pool guest_images_disk started
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    trial1               active     no
    
  5. Turn on autostart

    Turn on autostart for the storage pool. Autostart configures the libvirtd service to start the storage pool when the service starts.
    # virsh pool-autostart trial1
    Pool trial1 marked as autostarted
    Verify that the trial1 pool has autostart set:
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    trial1               active     yes
    
  6. Verify the storage pool configuration

    Verify the storage pool was created correctly, the sizes reported correctly, and the state reports as running.
    # virsh pool-info trial1
    Name:           trial1
    UUID:           afcc5367-6770-e151-bcb3-847bc36c5e28
    State:          running
    Persistent:     unknown
    Autostart:      yes
    Capacity:       100.31 GB
    Allocation:     0.00
    Available:      100.31 GB
    
An iSCSI-based storage pool is now available.

26.1.6. NFS-based storage pools

This procedure covers creating a storage pool with a NFS mount point in virt-manager.

26.1.6.1. Creating a NFS-based storage pool with virt-manager

  1. Open the host storage tab

    Open the Storage tab in the Host Details window.
    1. Open virt-manager.
    2. Select a host from the main virt-manager window.
    3. Open the Edit menu and select Host Details.
    4. Click on the Storage tab of the Host Details window.
  2. Create a new pool (part 1)

    Press the + button (the add pool button). The Add a New Storage Pool wizard appears.
    Choose a name for the storage pool and press Forward to continue.
  3. Create a new pool (part 2)

    Enter the target path for the device, the hostname and the NFS share path. Set the Format option to NFS or auto (to detect the type). The target path must be identical on all hosts for migration.
    Enter the hostname or IP address of the NFS server. This example uses server1.example.com.
    Enter the NFS path. This example uses /nfstrial.
    Press Finish to create the new storage pool.

Chapter 27.  Volumes

27.1. Creating volumes

This section shows how to create disk volumes inside a block based storage pool.
# virsh vol-create-as guest_images_disk volume1 8G
Vol volume1 created

# virsh vol-create-as guest_images_disk volume2 8G
Vol volume2 created

# virsh vol-create-as guest_images_disk volume3 8G
Vol volume3 created

# virsh vol-list guest_images_disk
Name                 Path
-----------------------------------------
volume1              /dev/sdb1
volume2              /dev/sdb2
volume3              /dev/sdb3

# parted -s /dev/sdb print
Model: ATA ST3500418AS (scsi)
Disk /dev/sdb: 500GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start   End     Size    File system  Name     Flags
2      17.4kB  8590MB  8590MB               primary
3      8590MB  17.2GB  8590MB               primary
1      21.5GB  30.1GB  8590MB               primary

#

27.2. Cloning volumes

Placeholder : Needs to describe what "cloning" means in this regard
The new volume will be allocated from storage in the same storage pool as the volume being cloned.
# virsh vol-clone --pool guest_images_disk volume3 clone1
Vol clone1 cloned from volume3

# virsh vol-list guest_images_disk
Name                 Path                                    
-----------------------------------------
clone1               /dev/sdb1                               
volume2              /dev/sdb2                               
volume3              /dev/sdb3                               

# parted -s /dev/sdb print
Model: ATA ST3500418AS (scsi)
Disk /dev/sdb: 500GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start   End     Size    File system  Name     Flags
2      8590MB  17.2GB  8590MB               primary
3      17.2GB  25.8GB  8590MB               primary
1      25.8GB  34.4GB  8590MB               primary

#

27.3. Adding storage devices to guests

This section covers adding storage devices to a virtualized guest. Additional storage can only be added after guests are created.

27.3.1. Adding file based storage to a guest

File-based storage or file-based containers are files on the hosts file system which act as virtualized hard drives for virtualized guests. To add a file-based container perform the following steps:
  1. Create an empty container file or using an existing file container (such as an ISO file).
    1. Create a sparse file using the dd command. Sparse files are not recommended due to data integrity and performance issues. Sparse files are created much faster and can used for testing but should not be used in production environments.
      # dd if=/dev/zero of=/var/lib/libvirt/images/FileName.img bs=1M seek=4096 count=0
      
    2. Non-sparse, pre-allocated files are recommended for file-based storage images. Create a non-sparse file, execute:
      # dd if=/dev/zero of=/var/lib/libvirt/images/FileName.img bs=1M count=4096
      
    Both commands create a 400MB file which can be used as additional storage for a virtualized guest.
  2. Dump the configuration for the guest. In this example the guest is called Guest1 and the file is saved in the users home directory.
    # virsh dumpxml Guest1 > ~/Guest1.xml
    
  3. Open the configuration file (Guest1.xml in this example) in a text editor. Find the <disk> elements, these elements describe storage devices. The following is an example disk element:
    <disk type='file' device='disk'>
         <driver name='virtio' cache='none'/>
        <source file='/var/lib/libvirt/images/Guest1.img'/>
        <target dev='sda'/>
    </disk>
    
  4. Add the additional storage by duplicating or writing a new <disk> element. Ensure you specify a device name for the virtual block device attributes. These attributes must be unique for each guest configuration file. The following example is a configuration file section which contains an additional file-based storage container named FileName.img.
    <disk type='file' device='disk'>
        <driver name='virtio' cache='none'/>
        <source file='/var/lib/libvirt/images/Guest1.img'/>
        <target dev='sda'/>
    </disk>
    <disk type='file' device='disk'>
         <driver name='virtio' cache='none'/>
        <source file='/var/lib/libvirt/images/FileName.img'/>
        <target dev='sdb'/>
    </disk>
    
  5. Restart the guest from the updated configuration file.
    # virsh create Guest1.xml
    
  6. The following steps are Linux guest specific. Other operating systems handle new storage devices in different ways. For other systems, refer to that operating system's documentation
    The guest now uses the file FileName.img as the device called /dev/sdb. This device requires formatting from the guest. On the guest, partition the device into one primary partition for the entire device then format the device.
    1. Press n for a new partition.
      # fdisk /dev/sdb
      Command (m for help):
      
    2. Press p for a primary partition.
      Command action
      e   extended
      p   primary partition (1-4)
      
    3. Choose an available partition number. In this example the first partition is chosen by entering 1.
      Partition number (1-4): 1
    4. Enter the default first cylinder by pressing Enter.
      First cylinder (1-400, default 1):
      
    5. Select the size of the partition. In this example the entire disk is allocated by pressing Enter.
      Last cylinder or +size or +sizeM or +sizeK (2-400, default 400):
      
    6. Set the type of partition by pressing t.
      Command (m for help): t
    7. Choose the partition you created in the previous steps. In this example, the partition number is 1.
      Partition number (1-4): 1
    8. Enter 83 for a linux partition.
      Hex code (type L to list codes): 83
    9. write changes to disk and quit.
      Command (m for help): w 
      Command (m for help): q
    10. Format the new partition with the ext3 file system.
      # mke2fs -j /dev/sdb1
  7. Mount the disk on the guest.
    # mount /dev/sdb1 /myfiles
The guest now has an additional virtualized file-based storage device.

27.3.2. Adding hard drives and other block devices to a guest

System administrators use additional hard drives to provide increased storage space for a guest, or to separate system data from user data.
Procedure 27.1. Adding physical block devices to virtualized guests
This procedure describes how to add a hard drive on the host to a virtualized guest. It applies to all physical block devices, including CD-ROM, DVD and floppy devices.
  1. Physically attach the hard disk device to the host. Configure the host if the drive is not accessible by default.
  2. Configure the device with multipath and persistence on the host if required.
  3. Use the virsh attach command as below, replacing:
    # virsh attach-disk myguest /dev/sdb1 sdc --driver tap --mode readonly
    • myguest with the name of the guest.
    • /dev/sdb1 with the device on the host to add.
    • sdc with the location on the guest where the device should be added. It must be an unused device name.
      Use the sd* notation for Windows guests as well, the guest will recognize the device correctly.
    • Only include the --mode readonly parameter if the device should be read only to the guest.
    Additionally, there are optional arguments that may be added:
    • Append the --type hdd parameter to the command for CD-ROM or DVD devices.
    • Append the --type floppy parameter to the command for floppy devices.
  4. The guest now has a new hard disk device called /dev/sdb on Linux or D: drive, or similar, on Windows. This device may require formatting.

Block device security - disk labels

The host should not use disk labels to identify file systems in the fstab file, the initrd file or on the kernel command line. Doing so presents a security risk if less privileged users, such as virtualized guests, have write access to whole partitions or LVM volumes.
A virtualized guest could write a disk label belonging to the host, to its own block device storage. Upon reboot of the host, the host could then mistakenly use the virtualized guests disk as a system disk, compromising the host system.

Block device security - whole disk access

Guests should not be given write access to whole disks or block devices (for example, /dev/sdb). Virtualized guests with access to block devices may be able to access other block devices on the system or modify volume labels which can be used to compromise the host system. Use partitions (for example, /dev/sdb1) or LVM volumes to prevent this issue.

27.4. Deleting and removing volumes

This section shows how to delete a disk volume from a block based storage pool.
# virsh vol-delete --pool guest_images_disk volume1
Vol volume1 deleted

# virsh vol-list guest_images_disk
Name                 Path                                    
-----------------------------------------
volume2              /dev/sdb2                               
volume3              /dev/sdb3                               

# parted -s /dev/sdb print
Model: ATA ST3500418AS (scsi)
Disk /dev/sdb: 500GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start   End     Size    File system  Name     Flags
2      8590MB  17.2GB  8590MB               primary
3      17.2GB  25.8GB  8590MB               primary

#

Chapter 28. Miscellaneous storage topics

28.1. Creating a virtualized floppy disk controller

Floppy disk controllers are required for a number of older operating systems, especially for installing drivers. Presently, physical floppy disk devices cannot be accessed from virtualized guests. However, creating and accessing floppy disk images from virtualized floppy drives should work. This section covers creating a virtualized floppy device.
An image file of a floppy disk is required. Create floppy disk image files with the dd command. Replace /dev/fd0 with the name of a floppy device and name the disk appropriately.
# dd if=/dev/fd0 of=~/legacydrivers.img
This example uses a guest created with virt-manager running a fully virtualized Fedora installation with an image located in /var/lib/libvirt/images/Fedora.img.
  1. Create the XML configuration file for your guest image using the virsh command on a running guest.
    # virsh dumpxml Fedora > Fedora.xml
    
    This saves the configuration settings as an XML file which can be edited to customize the operations and devices used by the guest. For more information on using the virsh XML configuration files, refer to Chapter 33, Creating custom libvirt scripts.
  2. Create a floppy disk image for the guest.
    # dd if=/dev/zero of=/var/lib/libvirt/images/Fedora-floppy.img bs=512 count=2880
    
  3. Add the content below, changing where appropriate, to your guest's configuration XML file. This example is an emulated floppy device using a file-based image.
    <disk type='file' device='floppy'>
    	<source file='/var/lib/libvirt/images/Fedora-floppy.img'/>
    	<target dev='fda'/>
    </disk>
    
  4. Force the guest to stop. To shut down the guest gracefully, use the virsh shutdown command instead.
    # virsh destroy Fedora
  5. Restart the guest using the XML configuration file.
    # virsh create Fedora.xml
    
The floppy device is now available in the guest and stored as an image file on the host.

28.2. Configuring persistent storage in Red Hat Enterprise Linux 6

This section is for systems with external or networked storage; for example, Fibre Channel, iSCSI, or SRP based storage devices. It is recommended that those systems have persistent device names configured for your hosts. This assists live migration as well as providing consistent device names and storage for multiple virtualized systems.
Universally Unique Identifiers (UUIDs) are a standardized method for identifying computers and devices in distributed computing environments. This section uses UUIDs to identify iSCSI, SRP, or Fibre Channel LUNs. UUIDs persist after restarts, disconnection and device swaps. The UUID is similar to a label on the device.
Systems which are not running multipath must use Single path configuration. Systems running multipath can use Multiple path configuration.
Single path configuration
This procedure implements LUN device persistence using udev. Only use this procedure for hosts which are not using multipath.
  1. Edit the /etc/scsi_id.config file.
    1. Add the following line:
      options=--whitelisted --replace-whitespace
      
      This sets the default options for scsi_id, ensuring returned UUIDs contains no spaces. The IET iSCSI target otherwise returns spaces in UUIDs, which can cause problems.
  2. To display the UUID for a given device run the scsi_id --whitelisted --replace-whitespace --device=/dev/sd* command. For example:
    # scsi_id --whitelisted --replace-whitespace --device=/dev/sdc
    1IET_00010001
    
    The output may vary from the example above. The output in this example displays the UUID of the device /dev/sdc.
  3. Verify the UUID output from the scsi_id --whitelisted --replace-whitespace --device=/dev/sd* command is correct and as expected.
  4. Create a rule to name the device. Create a file named 20-names.rules in the /etc/udev/rules.d directory. Add new rules to this file. All rules are added to the same file using the same format. Rules follow this format:
    KERNEL=="sd*", SUBSYSTEM=="block", PROGRAM="/sbin/scsi_id --whitelisted --replace-whitespace /dev/$name", RESULT=="UUID", NAME="devicename"
    
    Replace UUID and devicename with the UUID retrieved above, and a name for the device. This is an example for the rule above for three example iSCSI luns:
    KERNEL=="sd*", SUBSYSTEM=="block", PROGRAM="/sbin/scsi_id --whitelisted --replace-whitespace /dev/$name", RESULT=="1IET_00010001", NAME="rack4row16lun1"
    KERNEL=="sd*", SUBSYSTEM=="block", PROGRAM="/sbin/scsi_id --whitelisted --replace-whitespace /dev/$name", RESULT=="1IET_00010002", NAME="rack4row16lun2"
    KERNEL=="sd*", SUBSYSTEM=="block", PROGRAM="/sbin/scsi_id --whitelisted --replace-whitespace /dev/$name", RESULT=="1IET_00010003", NAME="rack4row16lun3"
    
    The udev daemon now searches all devices named /dev/sd* for a matching UUID in the rules. When a matching device is connected to the system the device is assigned the name from the rule. For example:
    # ls -la /dev/rack4row16*
    brw-rw---- 1 root disk 8, 18 May 25 23:35 /dev/rack4row16lun1
    brw-rw---- 1 root disk 8, 34 May 25 23:35 /dev/rack4row16lun2
    brw-rw---- 1 root disk 8, 50 May 25 23:35 /dev/rack4row16lun3
    
  5. Copy the changes in /etc/scsi_id.config and /etc/udev/rules.d/20-names.rules to all relevant hosts.
Networked storage devices with configured rules now have persistent names on all hosts where the files were updated This means you can migrate guests between hosts using the shared storage and the guests can access the storage devices in their configuration files.
Multiple path configuration
The multipath package is used for systems with more than one physical path from the computer to storage devices. multipath provides fault tolerance, fail-over and enhanced performance for network storage devices attached to Red Hat Enterprise Linux 6 systems.
Implementing LUN persistence in a multipath environment requires defined alias names for your multipath devices. Each storage device has a UUID, also known as a World Wide Identifier or WWID, which acts as a key for the aliased names.
This procedure implements LUN device persistence using the multipath daemon.
  1. Determine the World Wide Identifier of each device using the scsi_id --whitelisted --replace-whitespace --device=/dev/sd* command:
    # scsi_id --whitelisted --replace-whitespace --device=/dev/sde
    1IET_00010004
    # scsi_id --whitelisted --replace-whitespace --device=/dev/sdf
    1IET_00010005
    # scsi_id --whitelisted --replace-whitespace --device=/dev/sdg
    1IET_00010006
    # scsi_id --whitelisted --replace-whitespace --device=/dev/sdh
    1IET_00010007
    
  2. Create the multipath configuration file, /etc/multipath.conf. In it create a defaults section, and disable the user_friendly_names option unless you have a specific need for it. It is also a good idea to configure the default arguments for the getuid_callout option. This is generally a useful start:
    defaults {
    	user_friendly_names no
    	getuid_callout      "/sbin/scsi_id --whitelisted --replace-whitespace --device=/dev/%n"
    }
    
  3. Below the defaults section add a multipaths section (note the plural spelling). In this section add each of the WWIDs identified from the scsi_id command above. For example:
    multipaths {
    	multipath {
    		wwid			1IET_00010004
    		alias			oramp1
    	}
    
    	multipath {
    		wwid			1IET_00010005
    		alias			oramp2
    	}
    
    	multipath {
    		wwid			1IET_00010006
    		alias			oramp3
    	}
    
    	multipath {
    		wwid			1IET_00010007
    		alias			oramp4
    	}
    }
    
    Multipath devices are created in the /dev/mapper directory. The above example will create 4 LUNs named /dev/mapper/oramp1, /dev/mapper/oramp2, /dev/mapper/oramp3 and /dev/mapper/oramp4.
  4. Enable the multipathd daemon to start at system boot.
    # chkconfig multipathd on
    # chkconfig --list multipathd
    multipathd     	0:off	1:off	2:on	3:on	4:on	5:on	6:off
    
  5. The mapping of these device WWIDs to their alias names will now persist across reboots. For example:
    # ls -la /dev/mapper/oramp*
    brw-rw---- 1 root disk 253, 6 May 26 00:17 /dev/mapper/oramp1
    brw-rw---- 1 root disk 253, 7 May 26 00:17 /dev/mapper/oramp2
    brw-rw---- 1 root disk 253, 8 May 26 00:17 /dev/mapper/oramp3
    brw-rw---- 1 root disk 253, 9 May 26 00:17 /dev/mapper/oramp4
    # multipath -ll
    oramp1 (1IET_00010004) dm-6 IET,VIRTUAL-DISK
    size=20.0G features='0' hwhandler='0' wp=rw
    |-+- policy='round-robin 0' prio=1 status=active
    | `- 8:0:0:4  sde  8:64   active ready running
    `-+- policy='round-robin 0' prio=1 status=enabled
      `- 9:0:0:4  sdbl 67:240 active ready running
    oramp3 (1IET_00010006) dm-8 IET,VIRTUAL-DISK
    size=20.0G features='0' hwhandler='0' wp=rw
    |-+- policy='round-robin 0' prio=1 status=active
    | `- 8:0:0:6  sdg  8:96   active ready running
    `-+- policy='round-robin 0' prio=1 status=enabled
      `- 9:0:0:6  sdbn 68:16  active ready running
    oramp2 (1IET_00010005) dm-7 IET,VIRTUAL-DISK
    size=20.0G features='0' hwhandler='0' wp=rw
    |-+- policy='round-robin 0' prio=1 status=active
    | `- 8:0:0:5  sdf  8:80   active ready running
    `-+- policy='round-robin 0' prio=1 status=enabled
      `- 9:0:0:5  sdbm 68:0   active ready running
    oramp4 (1IET_00010007) dm-9 IET,VIRTUAL-DISK
    size=20.0G features='0' hwhandler='0' wp=rw
    |-+- policy='round-robin 0' prio=1 status=active
    | `- 8:0:0:7  sdh  8:112  active ready running
    `-+- policy='round-robin 0' prio=1 status=enabled
      `- 9:0:0:7  sdbo 68:32  active ready running
    

28.3. Accessing data from a guest disk image

There are various methods for accessing the data from guest image files. One common method is to use the kpartx tool, covered by this section, to mount the guest file system as a loop device which can then be accessed.
The kpartx command creates device maps from partition tables. Each guest storage image has a partition table embedded in the file.
The libguestfs and guestfish packages, available from the EPEL repository, allow advanced modification and access to guest file systems. The libguestfs and guestfish packages are not covered in this section at this time.

Warning

Guests must be offline before their files can be read. Editing or reading files of an active guest is not possible and may cause data loss or damage.
Procedure 28.1. Accessing guest image data
  1. Install the kpartx package.
    # yum install kpartx
  2. Use kpartx to list partition device mappings attached to a file-based storage image. This example uses a image file named guest1.img.
    # kpartx -l /var/lib/libvirt/images/guest1.img
    loop0p1 : 0 409600 /dev/loop0 63
    loop0p2 : 0 10064717 /dev/loop0 409663
    
    guest1 is a Linux guest. The first partition is the boot partition and the second partition is an EXT3 containing the root partition.
  3. Add the partition mappings to the recognized devices in /dev/mapper/.
    # kpartx -a /var/lib/libvirt/images/guest1.img
    1. Test that the partition mapping worked. There should be new devices in the /dev/mapper/ directory
      # ls /dev/mapper/
      loop0p1
      loop0p2
      
      The mappings for the image are named in the format loopXpY.
  4. Mount the loop device which to a directory. If required, create the directory. This example uses /mnt/guest1 for mounting the partition.
    # mkdir /mnt/guest1
    # mount /dev/mapper/loop0p1 /mnt/guest1 -o loop,ro
    
  5. The files are now available for reading in the /mnt/guest1 directory. Read or copy the files.
  6. Unmount the device so the guest image can be reused by the guest. If the device is mounted the guest cannot access the image and therefore cannot start.
    # umount /mnt/guest1
    
  7. Disconnect the image file from the partition mappings.
    # kpartx -d /var/lib/libvirt/images/guest1.img
The guest can now be restarted.
Accessing data from guest LVM volumes
Many Linux guests use Logical Volume Management (LVM) volumes. Additional steps are required to read data on LVM volumes on virtual storage images.
  1. Add the partition mappings for the guest1.img to the recognized devices in the /dev/mapper/ directory.
    # kpartx -a /var/lib/libvirt/images/guest1.img
  2. In this example the LVM volumes are on a second partition. The volumes require a rescan with the vgscan command to find the new volume groups.
    # vgscan
    Reading all physical volumes . This may take a while...
    Found volume group "VolGroup00" using metadata type lvm2
  3. Activate the volume group on the partition (called VolGroup00 by default) with the vgchange -ay command.
    # vgchange -ay VolGroup00
    2 logical volumes in volume group VolGroup00 now active.
    
  4. Use the lvs command to display information about the new volumes. The volume names (the LV column) are required to mount the volumes.
    # lvs
    LV VG Attr Lsize Origin Snap% Move Log Copy%
    LogVol00 VolGroup00 -wi-a- 5.06G
    LogVol01 VolGroup00 -wi-a- 800.00M
    
  5. Mount /dev/VolGroup00/LogVol00 in the /mnt/guestboot/ directory.
    # mount /dev/VolGroup00/LogVol00 /mnt/guestboot
  6. The files are now available for reading in the /mnt/guestboot directory. Read or copy the files.
  7. Unmount the device so the guest image can be reused by the guest. If the device is mounted the guest cannot access the image and therefore cannot start.
    # umount /mnt/guestboot
    
  8. Disconnect the volume group VolGroup00
    # vgchange -an VolGroup00
  9. Disconnect the image file from the partition mappings.
    # kpartx -d /var/lib/libvirt/images/guest1.img
The guest can now be restarted.

Chapter 29. N_Port ID Virtualization (NPIV)

N_Port ID Virtualization (NPIV) is a function available with some Fibre Channel devices. NPIV shares a single physical N_Port as multiple N_Port IDs. NPIV provides similar functionality for Host Bus Adaptors (HBAs) that SR-IOV provides for network interfaces. With NPIV, virtualized guests can be provided with a virtual Fibre Channel initiator to Storage Area Networks (SANs).
N_Ports are addressed with a 24 bit N_Port ID, which is assigned by the Fibre Channel switch.
Why use NPIV
  • Without NPIV virtualized guests must share an HBA's WWN on the SAN. With NPIV, it is possible to use LUN masking and zoning for virtualized guest.
  • With NPIV migration with zones and LUN masking is possible.
  • Physical HBAs are expensive and use an expansion slot. With NPIV, more guests can access SAN resources and guest density can be increased.
Each N_Port has a unique identity (port WWN and node WWN) on the SAN and can be used for zoning and LUN masking. Soft zoning, which you can use to group ports together by port WWN, is the preferred method of zoning.

29.1. Enabling NPIV on the switch

Enabling the NPIV on a Fibre Channel port on a switch
admin> portcfgshow 0
......
NPIV capability                    ON
......
Usage
portCfgNPIVPort <PortNumber> <Mode>
Mode      Meaning
0             Disable the NPIV capability on the port
1             Enable the NPIV capability on the port
Example:
admin> portCfgNPIVPort 0 1

29.1.1. Identifying HBAs in a Host System

To determine the types of HBAs in the system, enter the following command:
# ls /proc/scsi
QLogic HBAs are listed as qla2xxx. Emulex HBAs are listed as lpfc.
QLogic Example
# ls /proc/scsi/qla2xxx
Emulex Example
# ls /proc/scsi/lpfc

29.1.2. Verify NPIV is used on the HBA

Output the data from the kernel on the port nodes of the HBA.
Example 29.1. QLogic controller example
# cat /proc/scsi/qla2xxx/7
FC Port Information for Virtual Ports:
Virtual Port index = 1
Virtual Port 1:VP State = <ACTIVE>, Vp Flags = 0x0
scsi­qla2­port­3=500601609020fd54:500601601020fd54:a00000:1000: 1;
scsi­qla2­port­4=500601609020fd54:500601681020fd54:a10000:1000: 1;
Virtual Port 1 SCSI LUN Information:
( 0:10): Total reqs 10, Pending reqs 0, flags 0x0, 2:0:1000,

Example 29.2. Emulex controller example
# cat /proc/scsi/lpfc/3
SLI Rev: 3
NPIV Supported: VPIs max 127 VPIs used 1
RPIs max 512 RPIs used 13
Vports list on this physical port:
Vport DID 0x2f0901, vpi 1, state 0x20
Portname: 48:19:00:0c:29:00:00:0d Nodename: 48:19:00:0c:29:00:00:0b

29.1.2.1. Create and destroy a virtual HBA with NPIV

Issue an NPIV create call. Confirm that the host has started a new virtual HBA and that any storage zones are usable.
To create virtual HBAs using libvirt, you require a NPIV capable HBA and switch.
Confirm that you have those by manually creating a new HBA by printing the contents of the /sys/class/fc_host/hostN directory where class is the type of adaptor and fc_host is the host number.
Note that the WWN used below are for demonstrative purposes only. Use WWN customized for your SAN environment.
Add a new virtual HBA with the following command where '1111222233334444:5555666677778888' is WWPN:WWNN and host5 is the physical HBA which the virtual HBA is a client of.
# echo '1111222233334444:5555666677778888' > /sys/class/fc_host/host5/vport_create
If the creation is successful, a new HBA in the system with the next available host number.

Note

The virtual HBAs can be destroyed with the following command:
# echo '1111222233334444:5555666677778888' > /sys/class/fc_host/host5/vport_delete
Adding the virtual HBA with virsh
This procedure covers creating virtual HBA devices on a host with virsh. This procedure requires a compatible HBA device.
  1. List available HBAs

    Find the node device name of the HBA with the virtual adapters. List of all the HBAs on the host with the following command:
    # virsh nodedev-list -TODO-cap=scsi_host
    pci_10df_fe00_0_scsi_host
    pci_10df_fe00_0_scsi_host_0
    pci_10df_fe00_scsi_host
    pci_10df_fe00_scsi_host_0
    pci_10df_fe00_scsi_host_0_scsi_host
    pci_10df_fe00_scsi_host_0_scsi_host_0
  2. Gather parent HBA device data

    Output the XML definition for each required HBA. This example uses the HBA, pci_10df_fe00_scsi_host.
    # virsh nodedev-dumpxml pci_10df_fe00_scsi_host
    <device>
      <name>pci_10df_fe00_scsi_host</name>
      <parent>pci_10df_fe00</parent>
      <capability type='scsi_host'>
        <host>5</host>
        <capability type='fc_host'>
          <wwnn>20000000c9848140</wwnn>
          <wwpn>10000000c9848140</wwpn>
        </capability>
        <capability type='vport_ops' />
      </capability>
    </device>
    HBAs capable of creating virtual HBAs have a capability type='vport_ops' in the XML definition.
  3. Create the XML definition for the virtual HBA

    With information gathered in the previous step, create an XML definition for the virtual HBA. This example uses a file named newHBA.xml.
    <device>
      <parent>pci_10df_fe00_0_scsi_host</parent>
      <capability type='scsi_host'>
        <capability type='fc_host'>
          <wwpn>1111222233334444</wwpn>
          <wwnn>5555666677778888</wwnn>
        </capability>
      </capability>
    </device>
    The <parent> element is the name of the parent HBA listed by the virsh nodedev-list command. The <wwpn> and <wwnn> elements are the WWNN and WWPN for the virtual HBA.

    WWNN and WWPN validation

    Libvirt does not validate the WWPN or WWNN values, invalid WWNs are rejected by the kernel and libvirt reports the failure. The error reported by the kernel is similar to the following:
    # virsh nodedev-create badwwn.xml
    error: Failed to create node device from badwwn.xml
    error: Write of '1111222233334444:5555666677778888' to '/sys/class/fc_host/host6/vport_create' during vport create/delete failed: No such file or directory
  4. Create the virtual HBA

    Create the virtual HBA with the virsh nodedev-create command using the file from the previous step.
    # virsh nodedev-create newHBA.xml
    Node device pci_10df_fe00_0_scsi_host_0_scsi_host created from newHBA.xml
    The new virtual HBA should be detected and available to the host. The create command output gives you the node device name of the newly created device.

Destroying a virtual HBA with virsh

To destroy the device, use virsh nodedev-destroy:
# virsh nodedev-destroy pci_10df_fe00_0_scsi_host_0_scsi_host
Destroyed node device 'pci_10df_fe00_0_scsi_host_0_scsi_host'

Part VI. Virtualization reference guide

Chapter 30. Managing guests with virsh

virsh is a command line interface tool for managing guests and the hypervisor.
The virsh command-line tool is built on the libvirt management API and operates as an alternative to the qemu-kvm command and the graphical virt-manager application. The virsh command can be used in read-only mode by unprivileged users or, with root access, full administration functionality. The virsh command is ideal for scripting virtualization administration.
virsh command quick reference
The following tables provide a quick reference for all virsh command line options.
Table 30.1. Guest management commands
Command Description
help Prints basic help information.
list Lists all guests.
dumpxml Outputs the XML configuration file for the guest.
create Creates a guest from an XML configuration file and starts the new guest.
start Starts an inactive guest.
destroy Forces a guest to stop.
define Outputs an XML configuration file for a guest.
domid Displays the guest's ID.
domuuid Displays the guest's UUID.
dominfo Displays guest information.
domname Displays the guest's name.
domstate Displays the state of a guest.
quit Quits the interactive terminal.
reboot Reboots a guest.
restore Restores a previously saved guest stored in a file.
resume Resumes a paused guest.
save Save the present state of a guest to a file.
shutdown Gracefully shuts down a guest.
suspend Pauses a guest.
undefine Deletes all files associated with a guest.
migrate Migrates a guest to another host.

The following virsh command options manage guest and hypervisor resources:
Table 30.2. Resource management options
Command Description
setmem Sets the allocated memory for a guest.
setmaxmem Sets maximum memory limit for the hypervisor.
setvcpus Changes number of virtual CPUs assigned to a guest.
vcpuinfo Displays virtual CPU information about a guest.
vcpupin Controls the virtual CPU affinity of a guest.
domblkstat Displays block device statistics for a running guest.
domifstat Displays network interface statistics for a running guest.
attach-device Attach a device to a guest, using a device definition in an XML file.
attach-disk Attaches a new disk device to a guest.
attach-interface Attaches a new network interface to a guest.
detach-device Detach a device from a guest, takes the same kind of XML descriptions as command attach-device.
detach-disk Detach a disk device from a guest.
detach-interface Detach a network interface from a guest.

The virsh commands for managing and creating storage pools and volumes.
For more information on using storage pools with virsh, refer to http://libvirt.org/formatstorage.html
Table 30.3. Storage Pool options
Command Description
find-storage-pool-sources Returns the XML definition for all storage pools of a given type that could be found.
find-storage-pool-sources port Returns data on all storage pools of a given type that could be found as XML. If the host and port are provided, this command can be run remotely.
pool-autostart Sets the storage pool to start at boot time.
pool-build The pool-build command builds a defined pool. This command can format disks and create partitions.
pool-create pool-create creates and starts a storage pool from the provided XML storage pool definition file.
pool-create-as name Creates and starts a storage pool from the provided parameters. If the --print-xml parameter is specified, the command prints the XML definition for the storage pool without creating the storage pool.
pool-define Creates a storage bool from an XML definition file but does not start the new storage pool.
pool-define-as name Creates but does not start, a storage pool from the provided parameters. If the --print-xml parameter is specified, the command prints the XML definition for the storage pool without creating the storage pool.
pool-destroy Permanently destroys a storage pool in libvirt. The raw data contained in the storage pool is not changed and can be recovered with the pool-create command.
pool-delete Destroys the storage resources used by a storage pool. This operation cannot be recovered. The storage pool still exists after this command but all data is deleted.
pool-dumpxml Prints the XML definition for a storage pool.
pool-edit Opens the XML definition file for a storage pool in the users default text editor.
pool-info Returns information about a storage pool.
pool-list Lists storage pools known to libvirt. By default, pool-list lists pools in use by active guests. The --inactive parameter lists inactive pools and the --all parameter lists all pools.
pool-undefine Deletes the definition for an inactive storage pool.
pool-uuid Returns the UUID of the named pool.
pool-name Prints a storage pool's name when provided the UUID of a storage pool.
pool-refresh Refreshes the list of volumes contained in a storage pool.
pool-start Starts a storage pool that is defined but inactive.

This table contains miscellaneous virsh commands:
Table 30.4. Miscellaneous options
Command Description
version Displays the version of virsh
nodeinfo Outputs information about the hypervisor

Connecting to the hypervisor
Connect to a hypervisor session with virsh:
# virsh connect {name}
Where {name} is the machine name (hostname) or URL of the hypervisor. To initiate a read-only connection, append the above command with --readonly.
Creating a virtual machine XML dump (configuration file)
Output a guest's XML configuration file with virsh:
# virsh dumpxml {guest-id, guestname or uuid}
This command outputs the guest's XML configuration file to standard out (stdout). You can save the data by piping the output to a file. An example of piping the output to a file called guest.xml:
# virsh dumpxml GuestID > guest.xml
This file guest.xml can recreate the guest (refer to Editing a guest's configuration file. You can edit this XML configuration file to configure additional devices or to deploy additional guests. Refer to Section 33.1, “Using XML configuration files with virsh” for more information on modifying files created with virsh dumpxml.
An example of virsh dumpxml output:
# virsh dumpxml r5b2-mySQL01
<domain type='kvm' id='13'>
    <name>r5b2-mySQL01</name>
    <uuid>4a4c59a7ee3fc78196e4288f2862f011</uuid>
    <bootloader>/usr/bin/pygrub</bootloader>
    <os>
        <type>linux</type>
        <kernel>/var/lib/libvirt/vmlinuz.2dgnU_</kernel>
	<initrd>/var/lib/libvirt/initrd.UQafMw</initrd>
        <cmdline>ro root=/dev/VolGroup00/LogVol00 rhgb quiet</cmdline>
    </os>
    <memory>512000</memory>
    <vcpu>1</vcpu>
    <on_poweroff>destroy</on_poweroff>
    <on_reboot>restart</on_reboot>
    <on_crash>restart</on_crash>
    <devices>
        <interface type='bridge'>
            <source bridge='br0'/>
            <mac address='00:16:3e:49:1d:11'/>
            <script path='bridge'/>
        </interface>
        <graphics type='vnc' port='5900'/>
        <console tty='/dev/pts/4'/>
    </devices>
</domain>
Creating a guest from a configuration file
Guests can be created from XML configuration files. You can copy existing XML from previously created guests or use the dumpxml option (refer to Creating a virtual machine XML dump (configuration file)). To create a guest with virsh from an XML file:
# virsh create configuration_file.xml
Editing a guest's configuration file
Instead of using the dumpxml option (refer to Creating a virtual machine XML dump (configuration file)) guests can be edited either while they run or while they are offline. The virsh edit command provides this functionality. For example, to edit the guest named softwaretesting:
# virsh edit softwaretesting
This opens a text editor. The default text editor is the $EDITOR shell parameter (set to vi by default).
Suspending a guest
Suspend a guest with virsh:
# virsh suspend {domain-id, domain-name or domain-uuid}
When a guest is in a suspended state, it consumes system RAM but not processor resources. Disk and network I/O does not occur while the guest is suspended. This operation is immediate and the guest can be restarted with the resume (Resuming a guest) option.
Resuming a guest
Restore a suspended guest with virsh using the resume option:
# virsh resume {domain-id, domain-name or domain-uuid}
This operation is immediate and the guest parameters are preserved for suspend and resume operations.
Save a guest
Save the current state of a guest to a file using the virsh command:
# virsh save {domain-name, domain-id or domain-uuid} filename
This stops the guest you specify and saves the data to a file, which may take some time given the amount of memory in use by your guest. You can restore the state of the guest with the restore (Restore a guest) option. Save is similar to pause, instead of just pausing a guest the present state of the guest is saved.
Restore a guest
Restore a guest previously saved with the virsh save command (Save a guest) using virsh:
# virsh restore filename
This restarts the saved guest, which may take some time. The guest's name and UUID are preserved but are allocated for a new id.
Shut down a guest
Shut down a guest using the virsh command:
# virsh shutdown {domain-id, domain-name or domain-uuid}
You can control the behavior of the rebooting guest by modifying the on_shutdown parameter in the guest's configuration file.
Rebooting a guest
Reboot a guest using virsh command:
#virsh reboot {domain-id, domain-name or domain-uuid}
You can control the behavior of the rebooting guest by modifying the on_reboot element in the guest's configuration file.
Forcing a guest to stop
Force a guest to stop with the virsh command:
# virsh destroy {domain-id, domain-name or domain-uuid}
This command does an immediate ungraceful shutdown and stops the specified guest. Using virsh destroy can corrupt guest file systems . Use the destroy option only when the guest is unresponsive.
Getting the domain ID of a guest
To get the domain ID of a guest:
# virsh domid {domain-name or domain-uuid}
Getting the domain name of a guest
To get the domain name of a guest:
# virsh domname {domain-id or domain-uuid}
Getting the UUID of a guest
To get the Universally Unique Identifier (UUID) for a guest:
# virsh domuuid {domain-id or domain-name}
An example of virsh domuuid output:
# virsh domuuid r5b2-mySQL01
4a4c59a7-ee3f-c781-96e4-288f2862f011
Displaying guest Information
Using virsh with the guest's domain ID, domain name or UUID you can display information on the specified guest:
# virsh dominfo {domain-id, domain-name or domain-uuid}
This is an example of virsh dominfo output:
# virsh dominfo r5b2-mySQL01
id:             13
name:           r5b2-mysql01
uuid:           4a4c59a7-ee3f-c781-96e4-288f2862f011
os type:      	linux
state:          blocked
cpu(s):         1
cpu time:     	11.0s
max memory:     512000 kb
used memory:    512000 kb
Displaying host information
To display information about the host:
# virsh nodeinfo
An example of virsh nodeinfo output:
# virsh nodeinfo
CPU model                    x86_64
CPU (s)                      8
CPU frequency                2895 Mhz
CPU socket(s)                2      
Core(s) per socket           2
Threads per core:            2
Numa cell(s)                 1
Memory size:                 1046528 kb
This displays the node information and the machines that support the virtualization process.
Editing a storage pool definition
The virsh pool-edit command takes the name or UUID for a storage pool and opens the XML definition file for a storage pool in the users default text editor.
The virsh pool-edit command is equivalent to running the following commands:
# virsh pool-dumpxml pool > pool.xml
# vim pool.xml
# virsh pool-define pool.xml

Note

The default editor is defined by the $VISUAL or $EDITOR environment variables, and default is vi.
Displaying the guests
To display the guest list and their current states with virsh:
# virsh list
Other options available include:
the --inactive option to list inactive guests (that is, guests that have been defined but are not currently active), and
the --all option lists all guests. For example:
# virsh list --all
 Id Name                 State
----------------------------------
  0 Domain-0             running
  1 Domain202            paused
  2 Domain010            inactive
  3 Domain9600           crashed
The output from virsh list is categorized as one of the six states (listed below).
  • The running state refers to guests which are currently active on a CPU.
  • Guests listed as blocked are blocked, and are not running or runnable. This is caused by a guest waiting on I/O (a traditional wait state) or guests in a sleep mode.
  • The paused state lists domains that are paused. This occurs if an administrator uses the pause button in virt-manager, xm pause or virsh suspend. When a guest is paused it consumes memory and other resources but it is ineligible for scheduling and CPU resources from the hypervisor.
  • The shutdown state is for guests in the process of shutting down. The guest is sent a shutdown signal and should be in the process of stopping its operations gracefully. This may not work with all guest operating systems; some operating systems do not respond to these signals.
  • Domains in the dying state are in is in process of dying, which is a state where the domain has not completely shut-down or crashed.
  • crashed guests have failed while running and are no longer running. This state can only occur if the guest has been configured not to restart on crash.
Displaying virtual CPU information
To display virtual CPU information from a guest with virsh:
# virsh vcpuinfo {domain-id, domain-name or domain-uuid}
An example of virsh vcpuinfo output:
# virsh vcpuinfo r5b2-mySQL01
VCPU:           0
CPU:            0
State:          blocked
CPU time:       0.0s
CPU Affinity:   yy
Configuring virtual CPU affinity
To configure the affinity of virtual CPUs with physical CPUs:
# virsh vcpupin domain-id vcpu cpulist
The domain-id parameter is the guest's ID number or name.
The vcpu parameter denotes the number of virtualized CPUs allocated to the guest.The vcpu parameter must be provided.
The cpulist parameter is a list of physical CPU identifier numbers separated by commas. The cpulist parameter determines which physical CPUs the VCPUs can run on.
Configuring virtual CPU count
To modify the number of CPUs assigned to a guest with virsh:
# virsh setvcpus {domain-name, domain-id or domain-uuid} count
The new count value cannot exceed the count above the amount specified when the guest was created.
Configuring memory allocation
To modify a guest's memory allocation with virsh :
# virsh setmem {domain-id or domain-name} count
You must specify the count in kilobytes. The new count value cannot exceed the amount you specified when you created the guest. Values lower than 64 MB are unlikely to work with most guest operating systems. A higher maximum memory value does not affect an active guests. If the new value is lower the available memory will shrink and the guest may crash.
Displaying guest block device information
Use virsh domblkstat to display block device statistics for a running guest.
# virsh domblkstat GuestName block-device
Displaying guest network device information
Use virsh domifstat to display network interface statistics for a running guest.
# virsh domifstat GuestName interface-device 
Migrating guests with virsh
A guest can be migrated to another host with virsh. Migrate domain to another host. Add --live for live migration. The migrate command accepts parameters in the following format:
# virsh migrate --live GuestName DestinationURL
The --live parameter is optional. Add the --live parameter for live migrations.
The GuestName parameter represents the name of the guest which you want to migrate.
The DestinationURL parameter is the URL or hostname of the destination system. The destination system requires:
  • Red Hat Enterprise Linux 5.4 (ASYNC update 4) or newer,
  • the same hypervisor version, and
  • the libvirt service must be started.
Once the command is entered you will be prompted for the root password of the destination system.
Managing virtual networks
This section covers managing virtual networks with the virsh command. To list virtual networks:
# virsh net-list
This command generates output similar to:
# virsh net-list
Name                 State      Autostart
-----------------------------------------
default              active     yes      
vnet1	             active     yes      
vnet2	             active     yes
To view network information for a specific virtual network:
# virsh net-dumpxml NetworkName
This displays information about a specified virtual network in XML format:
# virsh net-dumpxml vnet1
<network>
  <name>vnet1</name>
  <uuid>98361b46-1581-acb7-1643-85a412626e70</uuid>
  <forward dev='eth0'/>
  <bridge name='vnet0' stp='on' forwardDelay='0' />
  <ip address='192.168.100.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='192.168.100.128' end='192.168.100.254' />
    </dhcp>
  </ip>
</network>
Other virsh commands used in managing virtual networks are:
  • virsh net-autostart network-name — Autostart a network specified as network-name.
  • virsh net-create XMLfile — generates and starts a new network using an existing XML file.
  • virsh net-define XMLfile — generates a new network device from an existing XML file without starting it.
  • virsh net-destroy network-name — destroy a network specified as network-name.
  • virsh net-name networkUUID — convert a specified networkUUID to a network name.
  • virsh net-uuid network-name — convert a specified network-name to a network UUID.
  • virsh net-start nameOfInactiveNetwork — starts an inactive network.
  • virsh net-undefine nameOfInactiveNetwork — removes the definition of an inactive network.

Chapter 31. Managing guests with the Virtual Machine Manager (virt-manager)

This section describes the Virtual Machine Manager (virt-manager) windows, dialog boxes, and various GUI controls.
virt-manager provides a graphical view of hypervisors and guest on your system and on remote machines. You can use virt-manager to define virtualized guests. virt-manager can perform virtualization management tasks, including:
  • assigning memory,
  • assigning virtual CPUs,
  • monitoring operational performance,
  • saving and restoring, pausing and resuming, and shutting down and starting virtualized guests,
  • links to the textual and graphical consoles, and
  • live and offline migrations.

31.1. Starting virt-manager

To start virt-manager session open the Applications menu, then the System Tools menu and select Virtual Machine Manager (virt-manager).
The virt-manager main window appears.
Starting virt-manager
Figure 31.1. Starting virt-manager

Alternatively, virt-manager can be started remotely using ssh as demonstrated in the following command:
ssh -X host's address
[remotehost]# virt-manager
Using ssh to manage virtual machines and hosts is discussed further in Section 19.1, “Remote management with SSH”.

31.2. The Virtual Machine Manager main window

This main window displays all the running guests and resources used by guests. Select a virtualized guest by double clicking the guest's name.
Virtual Machine Manager main window
Figure 31.2. Virtual Machine Manager main window

31.3. The virtual hardware details window

The virtual hardware details window displays information about the virtual hardware configured for the virtualized guest. Virtual hardware resources can be added, removed and modified in this window. To access the virtual hardware details window, click on the icon in the toolbar.
The virtual hardware details icon
Figure 31.3. The virtual hardware details icon

Clicking the icon displays the virtual hardware details window.
The virtual hardware details window
Figure 31.4. The virtual hardware details window

31.4. Virtual Machine graphical console

This window displays a virtualized guest's graphical console. Virtualized guests use different techniques to export their local virtual framebuffers, but both technologies use VNC to make them available to the Virtual Machine Manager's console window. If your virtual machine is set to require authentication, the Virtual Machine graphical console prompts you for a password before the display appears.
Graphical console window
Figure 31.5. Graphical console window

A note on security and VNC

VNC is considered insecure by many security experts, however, several changes have been made to enable the secure usage of VNC for virtualization on Red Hat enterprise Linux. The guest machines only listen to the local host's loopback address (127.0.0.1). This ensures only those with shell privileges on the host can access virt-manager and the virtual machine through VNC.
Remote administration can be performed following the instructions in Chapter 19, Remote management of virtualized guests. TLS can provide enterprise level security for managing guest and host systems.
Your local desktop can intercept key combinations (for example, Ctrl+Alt+F11) to prevent them from being sent to the guest machine. You can use virt-managersticky key' capability to send these sequences. You must press any modifier key (Ctrl or Alt) 3 times and the key you specify gets treated as active until the next non-modifier key is pressed. Then you can send Ctrl-Alt-F11 to the guest by entering the key sequence 'Ctrl Ctrl Ctrl Alt+F1'.
SPICE is an alternative to VNC available for Red Hat Enterprise Linux.

31.5. Adding a remote connection

This procedure covers how to set up a connection to a remote system using virt-manager.
  1. To create a new connection open the File menu and select the Add Connection... menu item.
  2. The Add Connection wizard appears. Select the hypervisor. For Red Hat Enterprise Linux 6 systems select QEMU/KVM. Select Local for the local system or one of the remote connection options and click Connect. This example uses Remote tunnel over SSH which works on default installations. For more information on configuring remote connections refer to Chapter 19, Remote management of virtualized guests
    Add Connection
    Figure 31.6. Add Connection

  3. Enter the root password for the selected host when prompted.
A remote host is now connected and appears in the main virt-manager window.
Remote host in the main virt-manager window
Figure 31.7. Remote host in the main virt-manager window

31.6. Displaying guest details

You can use the Virtual Machine Monitor to view activity information for any virtual machines on your system.
To view a virtual system's details:
  1. In the Virtual Machine Manager main window, highlight the virtual machine that you want to view.
    Selecting a virtual machine to display
    Figure 31.8. Selecting a virtual machine to display

  2. From the Virtual Machine Manager Edit menu, select Virtual Machine Details.
    Displaying the virtual machine details
    Figure 31.9. Displaying the virtual machine details

    On the Virtual Machine window, select Overview from the navigation pane on the left hand side.
    The Overview view shows a summary of configuration details for the virtualized guest.
    Displaying guest details overview
    Figure 31.10. Displaying guest details overview

  3. Select Performance from the navigation pane on the left hand side.
    The Performance view shows a summary of guest performance, including CPU and Memory usage.
    Displaying guest performance details
    Figure 31.11. Displaying guest performance details

  4. Select Processor from the navigation pane on the left hand side. The Processor view allows you to view or change the current processor allocation.
    Processor allocation panel
    Figure 31.12. Processor allocation panel

  5. Select Memory from the navigation pane on the left hand side. The Memory view allows you to view or change the current memory allocation.
    Displaying memory allocation
    Figure 31.13. Displaying memory allocation

  6. Each virtual disk attached to the virtual machine is displayed in the navigation pane. Click on a virtual disk to modify or remove it.
    Displaying disk configuration
    Figure 31.14. Displaying disk configuration

  7. Each virtual network interface attached to the virtual machine is displayed in the nagivation pane. Click on a virtual network interface to modify or remove it.
    Displaying network configuration
    Figure 31.15. Displaying network configuration

31.7. Performance monitoring

Performance monitoring preferences can be modified with virt-manager's preferences window.
To configure Performance monitoring:
  1. From the Edit menu, select Preferences.
    Modifying guest preferences
    Figure 31.16. Modifying guest preferences

    The Preferences window appears.
  2. From the Stats tab specify the time in seconds or stats polling options.
    Configuring performance monitoring
    Figure 31.17. Configuring performance monitoring

31.8. Displaying CPU usage

To view the CPU usage for all virtual machines on your system:
  1. From the View menu, select Graph, then the CPU Usage check box.
    Selecting CPU usage
    Figure 31.18. Selecting CPU usage

  2. The Virtual Machine Manager shows a graph of CPU usage for all virtual machines on your system.
    Displaying CPU usage
    Figure 31.19. Displaying CPU usage

31.9. Displaying Disk I/O

To view the disk I/O for all virtual machines on your system:
  1. From the View menu, select Graph, then the Disk I/O check box.
    Selecting Disk I/O
    Figure 31.20. Selecting Disk I/O

  2. The Virtual Machine Manager shows a graph of Disk I/O for all virtual machines on your system.
    Displaying Disk I/O
    Figure 31.21. Displaying Disk I/O

31.10. Displaying Network I/O

To view the network I/O for all virtual machines on your system:
  1. From the View menu, select Graph, then the Network I/O check box.
    Selecting Network I/O
    Figure 31.22. Selecting Network I/O

  2. The Virtual Machine Manager shows a graph of Network I/O for all virtual machines on your system.
    Displaying Network I/O
    Figure 31.23. Displaying Network I/O

31.11. Managing a virtual network

To configure a virtual network on your system:
  1. From the Edit menu, select Host Details.
    Selecting a host's details
    Figure 31.24. Selecting a host's details

  2. This will open the Host Details menu. Click the Virtual Networks tab.
    Virtual network configuration
    Figure 31.25. Virtual network configuration

  3. All available virtual networks are listed on the left-hand box of the menu. You can edit the configuration of a virtual network by selecting it from this box and editing as you see fit.

31.12. Creating a virtual network

To create a virtual network on your system:
  1. Open the Host Details menu (refer to Section 31.11, “Managing a virtual network”) and click the Add Network button, identified by a plus sign (+) icon.
    Virtual network configuration
    Figure 31.26. Virtual network configuration

    This will open the Create a new virtual network window. Click Forward to continue.
    Creating a new virtual network
    Figure 31.27. Creating a new virtual network

  2. Enter an appropriate name for your virtual network and click Forward.
    Naming your virtual network
    Figure 31.28. Naming your virtual network

  3. Enter an IPv4 address space for your virtual network and click Forward.
    Choosing an IPv4 address space
    Figure 31.29. Choosing an IPv4 address space

  4. Define the DHCP range for your virtual network by specifying a Start and End range of IP addresses. Click Forward to continue.
    Selecting the DHCP range
    Figure 31.30. Selecting the DHCP range

  5. Select how the virtual network should connect to the physical network.
    Connecting to physical network
    Figure 31.31. Connecting to physical network

    If you select Forwarding to physical network, choose whether the Destination should be Any physical device or a specific physical device. Also select whether the Mode should be NAT or Routed.
    Click Forward to continue.
  6. You are now ready to create the network. Check the configuration of your network and click Finish.
    Ready to create network
    Figure 31.32. Ready to create network

  7. The new virtual network is now available in the Virtual Network tab of the Host Details window.
    New virtual network is now available
    Figure 31.33. New virtual network is now available

Chapter 32. libvirt configuration reference

This chapter provides is a references for various parameters of libvirt XML configuration files
Table 32.1. libvirt configuration files
Item Description
pae
Specifies the physical address extension configuration data.
apic
Specifies the advanced programmable interrupt controller configuration data.
memory
Specifies the memory size in megabytes.
vcpus
Specifies the numbers of virtual CPUs.
console
Specifies the port numbers to export the domain consoles to.
nic
Specifies the number of virtual network interfaces.
vif
Lists the randomly-assigned MAC addresses and bridges assigned to use for the domain's network addresses.
disk
Lists the block devices to export to the domain and exports physical devices to domain with read only access.
dhcp
Enables networking using DHCP.
netmask
Specifies the configured IP netmasks.
gateway
Specifies the configured IP gateways.
acpi
Specifies the advanced configuration power interface configuration data.

Chapter 33. Creating custom libvirt scripts

This section provides some information which may be useful to programmers and system administrators intending to write custom scripts to make their lives easier by using libvirt.
Chapter 24, Miscellaneous administration tasks is recommended reading for programmers thinking of writing new applications which use libvirt.

33.1. Using XML configuration files with virsh

virsh can handle XML configuration files. You may want to use this to your advantage for scripting large deployments with special options. You can add devices defined in an XML file to a running virtualized guest. For example, to add a ISO file as hdc to a running guest create an XML file:
# cat satelliteiso.xml
<disk type="file" device="disk">
	<driver name="file"/>
	<source file="/var/lib/libvirt/images/rhn-satellite-5.0.1-11-redhat-linux-as-i386-4-embedded-oracle.iso"/>
	<target dev="hdc"/>
	<readonly/>
</disk>
Run virsh attach-device to attach the ISO as hdc to a guest called "satellite" :
# virsh attach-device satellite satelliteiso.xml

Part VII. Troubleshooting

Introduction to troubleshooting and problem solving

The following chapters provide information to assist you in troubleshooting issues you may encounter using virtualization.

Important note on virtualization issues

Your particular problem may not appear in this book due to ongoing development which creates and fixes bugs. For the most up to date list of known bugs, issues and bug fixes read the Red Hat Enterprise Linux 6 Release Notes for your version and hardware architecture. The Release Notes can be found in the documentation section of the Red Hat website, www.redhat.com/docs/manuals/enterprise/.

If all else fails...

Contact Red Hat Global Support Services (https://www.redhat.com/apps/support/). Our staff can assist you in resolving your issues.

Chapter 34. Troubleshooting

This chapter covers common problems and solutions for Red Hat Enterprise Linux 6 virtualization issues.
This chapter is to give you, the reader, a background to identify where problems with virtualization technologies are. Troubleshooting takes practice and experience which are difficult to learn from a book. It is recommended that you experiment and test virtualization on Red Hat Enterprise Linux 6 to develop your troubleshooting skills.
If you cannot find the answer in this document there may be an answer online from the virtualization community. Refer to Section A.1, “Online resources” for a list of Linux virtualization websites.

34.1. Debugging and troubleshooting tools

This section summarizes the System Administrator applications, the networking utilities, and debugging tools. You can employ these standard System administration tools and logs to assist with troubleshooting:
  • kvm_stat
  • kvmtrace
  • vmstat
  • iostat
  • lsof
  • systemtap
  • crash
  • sysrq
  • sysrq t
  • sysrq w
These networking tools can assist with troubleshooting virtualization networking problems:
  • ifconfig
  • tcpdump
    The tcpdump command 'sniffs' network packets. tcpdump is useful for finding network abnormalities and problems with network authentication. There is a graphical version of tcpdump named wireshark.
  • brctl
    brctl is a networking tool that inspects and configures the Ethernet bridge configuration in the Virtualization linux kernel. You must have root access before performing these example commands:
    # brctl show 
    bridge-name    bridge-id          STP  enabled  interfaces  
    -----------------------------------------------------------------------------
    virtbr0             8000.feffffff       yes        eth0
    
    # brctl showmacs virtbr0 
    port-no           mac-addr                  local?       aging timer
    1                 fe:ff:ff:ff:ff:           yes            0.00
    2                 fe:ff:ff:fe:ff:           yes            0.00
    # brctl showstp virtbr0
    virtbr0 
    bridge-id              8000.fefffffffff
    designated-root        8000.fefffffffff
    root-port              0                   path-cost             0
    max-age                20.00               bridge-max-age        20.00
    hello-time             2.00                bridge-hello-time     2.00
    forward-delay          0.00                bridge-forward-delay  0.00
    aging-time            300.01
    hello-timer            1.43                tcn-timer             0.00
    topology-change-timer  0.00                gc-timer              0.02
    
Listed below are some other useful commands for troubleshooting virtualization.
  • strace is a command which traces system calls and events received and used by another process.
  • vncviewer: connect to a VNC server running on your server or a virtual machine. Install vncviwer using the yum install vnc command.
  • vncserver: start a remote desktop on your server. Gives you the ability to run graphical user interfaces such as virt-manager via a remote session. Install vncserver using the yum install vnc-server command.

34.2. kvm_stat

The kvm_stat command is a python script which retrieves runtime statistics from the kvm kernel module. The kvm_stat command can be used to diagnose guest behavior visible to kvm. In particular, performance related issues with guests. Currently, the reported statistics are for the entire system; the behavior of all running guests is reported.
The kvm_stat command requires that the kvm kernel module is loaded and debugfs is mounted. If either of these features are not enabled, the command will output the required steps to enable debugfs or the kvm module. For example:
# kvm_stat
Please mount debugfs ('mount -t debugfs debugfs /sys/kernel/debug')
and ensure the kvm modules are loaded
Mount debugfs if required:
# mount -t debugfs debugfs /sys/kernel/debug
kvm_stat output
The kvm_stat command outputs statistics for all virtualized guests and the host. The output is updated until the command is terminated (using Ctrl+c or the q key).
# kvm_stat

kvm statistics

efer_reload                 94       0
exits                  4003074   31272
fpu_reload             1313881   10796
halt_exits               14050     259
halt_wakeup               4496     203
host_state_reload	1638354   24893
hypercalls                   0       0
insn_emulation         1093850    1909
insn_emulation_fail          0       0
invlpg                   75569       0
io_exits               1596984   24509
irq_exits                21013     363
irq_injections           48039    1222
irq_window               24656     870
largepages                   0       0
mmio_exits               11873       0
mmu_cache_miss           42565       8
mmu_flooded              14752       0
mmu_pde_zapped           58730       0
mmu_pte_updated              6       0
mmu_pte_write           138795       0
mmu_recycled                 0       0
mmu_shadow_zapped        40358       0
mmu_unsync                 793       0
nmi_injections               0       0
nmi_window                   0       0
pf_fixed                697731    3150
pf_guest                279349       0
remote_tlb_flush             5       0
request_irq                  0       0
signal_exits                 1       0
tlb_flush               200190       0
Explanation of variables:
efer_reload
The number of Extended Feature Enable Register (EFER) reloads.
exits
The count of all VMEXIT calls.
fpu_reload
The number of times a VMENTRY reloaded the FPU state. The fpu_reload is incremented when a guest is using the Floating Point Unit (FPU).
halt_exits
Number of guest exits due to halt calls. This type of exit is usually seen when a guest is idle.
halt_wakeup
Number of wakeups from a halt.
host_state_reload
Count of full reloads of the host state (currently tallies MSR setup and guest MSR reads).
hypercalls
Number of guest hypervisor service calls.
insn_emulation
Number of guest instructions emulated by the host.
insn_emulation_fail
Number of failed insn_emulation attempts.
io_exits
Number of guest exits from I/O port accesses.
irq_exits
Number of guest exits due to external interrupts.
irq_injections
Number of interrupts sent to guests.
irq_window
Number of guest exits from an outstanding interrupt window.
largepages
Number of large pages currently in use.
mmio_exits
Number of guest exits due to memory mapped I/O (MMIO) accesses.
mmu_cache_miss
Number of KVM MMU shadow pages created.
mmu_flooded
Detection count of excessive write operations to an MMU page. This counts detected write operations not of individual write operations.
mmu_pde_zapped
Number of page directory entry (PDE) destruction operations.
mmu_pte_updated
Number of page table entry (PTE) destruction operations.
mmu_pte_write
Number of guest page table entry (PTE) write operations.
mmu_recycled
Number of shadow pages that can be reclaimed.
mmu_shadow_zapped
Number of invalidated shadow pages.
mmu_unsync
Number of non-synchronized pages which are not yet unlinked.
nmi_injections
Number of Non-maskable Interrupt (NMI) injections to the guest.
nmi_window
Number of guest exits from (outstanding) Non-maskable Interrupt (NMI) windows.
pf_fixed
Number of fixed (non-paging) page table entry (PTE) maps.
pf_guest
Number of page faults injected into guests.
remote_tlb_flush
Number of remote (sibling CPU) Translation Lookaside Buffer (TLB) flush requests.
request_irq
Number of guest interrupt window request exits.
signal_exits
Number of guest exits due to pending signals from the host.
tlb_flush
Number of tlb_flush operations performed by the hypervisor.

Note

The output information from the kvm_stat command is exported by the KVM hypervisor as pseudo files located in the /sys/kernel/debug/kvm/ directory.

34.3. Log files

KVM uses various log files. All the log files are standard ASCII files, and accessible with a text editor.
  • The default directory for all file-based images is the /var/lib/libvirt/images directory.
  • qemu-kvm.[PID].log is the log file created by the qemu-kvm process for each fully virtualized guest. When using this log file, you must retrieve the given qemu-kvm process PID, by using the ps command to examine process arguments to isolate the qemu-kvm process on the virtual machine. Note that you must replace the [PID] symbol with the actual PID qemu-kvm process.
If you encounter any errors with the Virtual Machine Manager, you can review the generated data in the virt-manager.log file that resides in the /.virt-manager directory. Note that every time you start the Virtual Machine Manager, it overwrites the existing log file contents. Make sure to backup the virt-manager.log file, before you restart the Virtual Machine manager after a system error.

34.4. Troubleshooting with serial consoles

Linux kernels can output information to serial ports. This is useful for debugging kernel panics and hardware issues with video devices or headless servers. The subsections in this section cover setting up serial console output for machines running Red Hat Enterprise Linux 6 virtualization kernels and their virtualized guests.
This section covers how to enable serial console output for fully virtualized guests.
Fully virtualized guest serial console output can be viewed with the virsh console command.
Be aware fully virtualized guest serial consoles have some limitations. Present limitations include:
  • output data may be dropped or scrambled.
The serial port is called ttyS0 on Linux or COM1 on Windows.
You must configure the virtualized operating system to output information to the virtual serial port.
To output kernel information from a fully virtualized Linux guest into the domain modify the /boot/grub/grub.conf file by inserting the line console=tty0 console=ttyS0,115200.
title Red Hat Enterprise Linux Server (2.6.32-36.x86-64)
	root (hd0,0)
	kernel /vmlinuz-2.6.32-36.x86-64 ro root=/dev/volgroup00/logvol00
	console=tty0 console=ttyS0,115200
	initrd /initrd-2.6.32-36.x86-64.img
Reboot the guest.
On the host, access the serial console with the following command:
# virsh console
You can also use virt-manager to display the virtual text console. In the guest console window, select Serial Console from the View menu.

34.5. Virtualization log files

  • /var/log/libvirt/qemu/GuestName.log
If you encounter any errors with the Virtual Machine Manager, you can review the generated data in the virt-manager.log file that resides in the /.virt-manager directory. Note that every time you start the Virtual Machine Manager, it overwrites the existing log file contents. Make sure to backup the virt-manager.log file, before you restart the Virtual Machine manager after a system error.

34.6. Loop device errors

If file-based guest images are used you may have to increase the number of configured loop devices. The default configuration allows up to eight active loop devices. If more than eight file-based guests or loop devices are needed the number of loop devices configured can be adjusted in /etc/modprobe.conf. Edit /etc/modprobe.conf and add the following line to it:
options loop max_loop=64
This example uses 64 but you can specify another number to set the maximum loop value. You may also have to implement loop device backed guests on your system. To use a loop device backed guests for a full virtualized system, use the phy: device or file: file commands.

34.7. Enabling Intel VT and AMD-V virtualization hardware extensions in BIOS

This section describes how to identify hardware virtualization extensions and enable them in your BIOS if they are disabled.
The Intel VT extensions can be disabled in the BIOS. Certain laptop vendors have disabled the Intel VT extensions by default in their CPUs.
The virtualization extensions cannot be disabled in the BIOS for AMD-V.
The virtualization extensions are sometimes disabled in BIOS, usually by laptop manufacturers. Refer to the following section for instructions on enabling disabled virtualization extensions.
Verify the virtualization extensions are enabled in BIOS. The BIOS settings for Intel® VT or AMD-V are usually in the Chipset or Processor menus. The menu names may vary from this guide, the virtualization extension settings may be found in Security Settings or other non standard menu names.
Procedure 34.1. Enabling virtualization extensions in BIOS
  1. Reboot the computer and open the system's BIOS menu. This can usually be done by pressing the delete key, the F1 key or Alt and F4 keys depending on the system.
  2. Enabling the virtualization extensions in BIOS

    Note: BIOS steps

    Many of the steps below may vary depending on your motherboard, processor type, chipset and OEM. Refer to your system's accompanying documentation for the correct information on configuring your system.
    1. Open the Processor submenu The processor settings menu may be hidden in the Chipset, Advanced CPU Configuration or Northbridge.
    2. Enable Intel Virtualization Technology (also known as Intel VT). AMD-V extensions cannot be disabled in the BIOS and should already be enabled. The virtualization extensions may be labeled Virtualization Extensions, Vanderpool or various other names depending on the OEM and system BIOS.
    3. Enable Intel VTd or AMD IOMMU, if the options are available. Intel VTd and AMD IOMMU are used for PCI passthrough.
    4. Select Save & Exit.
  3. Reboot the machine.
  4. When the machine has booted, run cat /proc/cpuinfo | grep vmx svm. If the command outputs, the virtualization extensions are now enabled. If there is no output your system may not have the virtualization extensions or the correct BIOS setting enabled.

34.8. KVM networking performance

By default, KVM virtual machines are assigned a virtual Realtek 8139 (rtl8139) NIC (network interface controller).
The rtl8139 virtualized NIC works fine in most environments. However, this device can suffer from performance degradation problems on some networks, for example, a 10 Gigabit Ethernet network.
To improve performance switch to the para-virtualized network driver.

Note

Note that the virtualized Intel PRO/1000 (e1000) driver is also supported as an emulated driver choice. To use the e1000 driver, replace virtio in the procedure below with e1000. For the best performance it is recommended to use the virtio driver.
Procedure 34.2. Switching to the virtio driver
  1. Shutdown the guest operating system.
  2. Edit the guest's configuration file with the virsh command (where GUEST is the guest's name):
    # virsh edit GUEST
    The virsh edit command uses the $EDITOR shell variable to determine which editor to use.
  3. Find the network interface section of the configuration. This section resembles the snippet below:
    <interface type='network'>
      [output truncated]
      <model type='rtl8139' />
    </interface>
    
  4. Change the type attribute of the model element from 'rtl8139' to 'virtio'. This will change the driver from the rtl8139 driver to the e1000 driver.
    <interface type='network'>
      [output truncated]
      <model type='virtio' />
    </interface>
    
  5. Save the changes and exit the text editor
  6. Restart the guest operating system.
Creating new guests using other network drivers
Alternatively, new virtualized guests can be created with a different network driver. This may be required if you are having difficulty installing guests over a network connection. This method requires you to have at least one virtualized guest already created (possibly installed from CD or DVD) to use as a template.
  1. Create an XML template from an existing virtualized guest (in this example, named Guest1):
    # virsh dumpxml Guest1 > /tmp/guest-template.xml
    
  2. Copy and edit the XML file and update the unique fields: virtual machine name, UUID, disk image, MAC address, and any other unique parameters. Note that you can delete the UUID and MAC address lines and virsh will generate a UUID and MAC address.
    # cp /tmp/guest-template.xml /tmp/new-guest.xml
    # vi /tmp/new-guest.xml
    
    Add the model line in the network interface section:
     <interface type='network'>
      [output truncated]
      <model type='virtio' />
    </interface>
    
  3. Create the new virtual machine:
    # virsh define /tmp/new-guest.xml
    # virsh start new-guest
    

Additional resources

To learn more about virtualization and Red Hat Enterprise Linux, refer to the following resources.

A.1. Online resources

A.2. Installed documentation

  • man virsh and /usr/share/doc/libvirt-<version-number> — Contains sub commands and options for the virsh virtual machine management utility as well as comprehensive information about the libvirt virtualization library API.
  • /usr/share/doc/gnome-applet-vm-<version-number> — Documentation for the GNOME graphical panel applet that monitors and manages locally-running virtual machines.
  • /usr/share/doc/libvirt-python-<version-number> — Provides details on the Python bindings for the libvirt library. The libvirt-python package allows python developers to create programs that interface with the libvirt virtualization management library.
  • /usr/share/doc/python-virtinst-<version-number> — Provides documentation on the virt-install command that helps in starting installations of Fedora and Red Hat Enterprise Linux related distributions inside of virtual machines.
  • /usr/share/doc/virt-manager-<version-number> — Provides documentation on the Virtual Machine Manager, which provides a graphical tool for administering virtual machines.

Glossary

This glossary is intended to define the terms used in this Installation Guide.
Bare-metal
The term bare-metal refers to the underlying physical architecture of a computer. Running an operating system on bare-metal is another way of referring to running an unmodified version of the operating system on the physical hardware. An example of operating system running on bare metal is a normally installed operating system.
Full virtualization
KVM uses full, hardware-assisted virtualization. Full virtualization uses hardware features of the processor to provide total abstraction of the underlying physical system (Bare-metal) and creates a new virtual machine in which the guest operating systems can run. No modifications are needed in the guest operating system. The guest operating system and any applications on the guest are not aware of the virtualized environment and run normally. Para-virtualization requires a modified version of the Linux operating system.
Fully virtualized
Guest system
Also known as guests, virtual machines, virtual servers or domains.
Hardware Virtual Machine
Host
The host operating system runs virtualized guests.
Hypervisor
The hypervisor is the software layer that abstracts the hardware from the operating system permitting multiple operating systems to run on the same hardware. The hypervisor runs on a host operating system allowing other virtualized operating systems to run on the host's hardware.
The Kernel-based Virtual Machine hypervisor is provided with Red Hat Enterprise Linux.
I/O
Short for input/output (pronounced "eye-oh"). The term I/O describes any program, operation or device that transfers data to or from a computer and to or from a peripheral device. Every transfer is an output from one device and an input into another. Devices such as keyboards and mouses are input-only devices while devices such as printers are output-only. A writable CD-ROM is both an input and an output device.
Kernel SamePage Merging
Kernel SamePage Merging (KSM) is used by the KVM hypervisor to allow KVM guests to share identical memory pages. The pages shared are usually common libraries or other identical, high-use data. KSM allows for greater guest density of identical or similar guest operating systems by avoiding memory duplication.
For information on using KSM with Red Hat Enterprise Linux refer to Chapter 21, KSM.
Kernel-based Virtual Machine
KVM (Kernel-based Virtual Machine) is a Full virtualization solution for Linux on AMD64 and Intel 64 hardware. KVM is a Linux kernel module built for the standard Red Hat Enterprise Linux kernel. KVM can run multiple, unmodified virtualized guest Windows and Linux operating systems. The KVM hypervisor in Red Hat Enterprise Linux is managed with the libvirt API and tools built for libvirt, virt-manager and virsh.
KVM is a set of Linux kernel modules which manage devices, memory and management APIs for the Hypervisor module itself. Virtualized guests are run as Linux processes and threads which are controlled by these modules.
Red Hat Enterprise Linux KVM hypervisors can be managed by the Red Hat Enterprise Virtualization Manager as an alternative to libvirt.
LUN
A Logical Unit Number (LUN) is a number assigned to a logical unit (a SCSI protocol entity).
MAC Addresses
The Media Access Control Address is the hardware address for a Network Interface Controller. In the context of virtualization MAC addresses must be generated for virtual network interfaces with each MAC on your local domain being unique.
Migration
Migration is the term for the process of moving a virtualized guest from one host to another. Migration can be conducted offline (where the guest is suspended and then moved) or live (where a guest is moved without suspending).
Offline migration
An offline migration suspends the guest then moves an image of the guest's memory to the destination host.
Live migration
Live migration is the process of migrating a running guest from one physical host to another physical host.
Para-virtualization
Para-virtualization is only available in Red Hat Enterprise Linux 5. Para-virtualization uses software mechanisms to share devices and system resources with specially-designed kernels or newer kernels with the PV-opts features.
Para-virtualized
Para-virtualized drivers
Para-virtualized drivers are device drivers that operate on fully virtualized Linux guests. These drivers greatly increase performance of network and block device I/O for fully virtualized guests.
PCI passthrough
The KVM hypervisor supports attaching PCI devices on the host system to virtualized guests. PCI passthrough allows guests to have exclusive access to PCI devices for a range of tasks. PCI passthrough allows PCI devices to appear and behave as if they were physically attached to the guest operating system.
Physical Functions
Physical Functions (PFs) are full PCIe devices that include the SR-IOV capabilities. Physical Functions are discovered, managed, and configured as normal PCI devices. Physical Functions configure and manage the SR-IOV functionality by assigning Virtual Functions.
Security Enhanced Linux
Short for Security Enhanced Linux, SELinux uses Linux Security Modules (LSM) in the Linux kernel to provide a range of minimum privilege required security policies.
Single Root I/O Virtualization
SR-IOV is a standard for a type of PCI passthrough which natively shares a single device to multiple guests.
SR-IOV enables a Single Root Function (for example, a single Ethernet port), to appear as multiple, separate, physical devices. A physical device with SR-IOV capabilities can be configured to appear in the PCI configuration space as multiple functions, each device has its own configuration space complete with Base Address Registers (BARs).
SR-IOV uses two new PCI functions:
Universally Unique Identifier
A Universally Unique Identifier (UUID) is a standardized numbering method for devices, systems and certain software objects in distributed computing environments. Types of UUIDs in virtualization include: ext2 and ext3 file system identifiers, RAID device identifiers, iSCSI and LUN device identifiers, MAC addresses and virtual machine identifiers.
Virtual Functions
Virtual Functions (VFs) are simple PCIe functions that only process I/O. Each Virtual Function is derived from a Physical Function. The number of Virtual Functions a device may have is limited by the device hardware. A single Ethernet port, the Physical Device, may map to many Virtual Functions that can be shared to virtualized guests.
Virtual machines
A virtual machine is a software implementation of a physical machine or programming language (for example the Java Runtime Environment or LISP). Virtual machines in the context of virtualization are operating systems running on virtualized hardware.
Virtualization
Virtualization is a broad computing term for running software, usually operating systems, concurrently and isolated from other programs on one system. Most existing implementations of virtualization use a hypervisor, a software layer that controls hardware and provides guest operating systems with access to underlying hardware. The hypervisor allows multiple operating systems to run on the same physical system by giving the guest operating system virtualized hardware. There are various methods for virtualizing operating systems:
  • Hardware-assisted virtualization is the technique used for full virtualization with KVM (definition: Full virtualization)
  • Para-virtualization is a technique used by Xen to run Linux guests (definition: Para-virtualization)
  • Software virtualization or emulation. Software virtualization uses binary translation and other emulation techniques to run unmodified operating systems. Software virtualization is significantly slower than hardware-assisted virtualization or para-virtualization. Software virtualization, in the form of QEMU or BORCH, works in Red Hat Enterprise Linux, it's just slow.
Red Hat Enterprise Linux supports hardware-assisted, full virtualization with the KVM hypervisor.
Virtualized CPU
A system has a number of virtual CPUs (VCPUs) relative to the number of physical processor cores. The number of virtual CPUs is finite and represents the total number of virtual CPUs that can be assigned to guest virtual machines.
Xen
Xen is not available as a hypervisor type for Red Hat Enterprise Linux 6 and newer. Xen is only supported for Red Hat Enterprise Linux 5 and newer.
Red Hat Enterprise Linux 5 supports the Xen hypervisor and the KVM hypervisor (refer to Kernel-based Virtual Machine). Both hypervisors have different architectures and development approaches. The Xen hypervisor runs underneath a Red Hat Enterprise Linux operating system which acts as a host managing system resources and virtualization APIs.
Red Hat Enterprise Linux 6 is supported as a para-virtualized and fully-virtualized guest of Red Hat Enterprise Linux 5.4 (and newer) running the Xen hypervisor. Red Hat Enterprise Linux 6 is also supported as a guest of the Red Hat Enterprise Linux 5.4 (and newer) running the KVM hypervisor.

Revision History

Revision History
Revision 6.0-35Mon Oct 04 2010Scott Radvan
Review for 6.0 release.
Revision 6.0-25Thu Sep 09 2010Christopher Curran
Resolves BZ#621740.
Revision 6.0-24Fri Sep 03 2010Christopher Curran
Updated para-virtualized driver usage procedures. BZ#621740.
Revision 6.0-23Tue May 25 2010Christopher Curran
New storage content BZ#536816.
Revision 6.0-22Fri May 14 2010Christopher Curran
Fixes BZ#587911, which expands supported storage devices.
Updated Introduction chapter
Updated Troubleshooting chapter
Updated KSM chapter
Updated overcommitting guidance.
Revision 6.0-11Tue Apr 20 2010Christopher Curran
Beta version update. Various fixes included.
Revision 6.0-10Thu Apr 15 2010Christopher Curran
Forward-ported the following fixes from the Red Hat Enterprise Linux 5.5 release:
Fixes BZ#573558, and expands SR-IOV content.
Fixes BZ#559052, expands the KVM para-virtualized drivers chapter.
Fixes BZ#578342.
Fixes BZ#573553.
Fixes BZ#573556.
Fixes BZ#573549.
Fixes BZ#534020.
Fixes BZ#573555.
Revision 6.0-5Mon Mar 01 2010Christopher Curran
Beta version released.

Colophon

This manual was written in the DocBook XML v4.3 format.
This book is based on the original work of Jan Mark Holzer, Justin Clift and Chris Curran.
This book is edited and maintained by Scott Radvan.
Other writing credits go to:
  • Daniel Berrange contributed various sections on libvirt.
  • Don Dutile contributed technical editing for the para-virtualized drivers section.
  • Barry Donahue contributed technical editing for the para-virtualized drivers section.
  • Rick Ring contributed technical editing for the Virtual Machine Manager Section.
  • Michael Kearey contributed technical editing for the sections on using XML configuration files with virsh and virtualized floppy drives.
  • Marco Grigull contributed technical editing for the software compatibility and performance section.
  • Eugene Teo contributed technical editing for the Managing Guests with virsh section.
Publican, the publishing tool which produced this book, was written by Jeffrey Fearn.
Translators
Due to technical limitations, the translators credited in this section are those who worked on previous versions of the Red Hat Enterprise Linux Virtualization Guide and the Fedora Virtualization Guide.
To find out who translated the current version of the guide, visit https://fedoraproject.org/wiki/Fedora_13_Documentation_Translations_-_Contributors. These translators will receive credit in subsequent versions of this guide.
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