Xen to KVM Migration Guide

This section contains information to help you import virtual machines from foreign hypervisors (such as Xen) to KVM managed by libvirt.

Tip: Microsoft Windows Guests

This section is focused on converting Linux guests. Converting Microsoft Windows guests using virt-v2v is the same as converting Linux guests, except in regards to handling the Virtual Machine Driver Pack (VMDP). Additional details on converting Windows guests with the VMDP can be found in the separate at Virtual Machine Driver Pack documentation.

> sudo zypper install virt-v2v

1.3 Preparing the Virtual Machine #

 

Note: Conditions for Skipping This Step

If running virt-v2v on SLES 12 SP1 or before, this step can be safely skipped. This step can also be ignored if the virtual machine is fully virtualized or if it runs on SLES 12 SP2 or later.

The Xen virtual machine must have default kernel installed. To ensure this, run zypper in kernel-default on the virtual machine.

1.4 Converting Virtual Machines to Run under KVM Managed by libvirt #

 

virt-v2v converts virtual machines from the Xen hypervisor to run under KVM managed by libvirt. To learn more about libvirt and virsh, see Part II, “Managing Virtual Machines with libvirt”. Additionally, all virt-v2v command line options are explained in the virt-v2v manual page (man 1 virt-v2v).

Before converting a virtual machine, make sure to complete the following steps:

Procedure 1: Preparing the Environment for the Conversion #

 

1. Create a new local storage pool.

   virt-v2v copies the storage of the source virtual machine to a local storage pool managed by libvirt (the original disk image remains unchanged). You can create the pool either with Virtual Machine Manager, or virsh. For more information, see Section 11.1, “Managing Storage with Virtual Machine Manager” and Section 11.2, “Managing Storage with virsh”.

2. Prepare the local network interface.

   Check that the converted virtual machine can use a local network interface on the VM Host Server. It is usually a network bridge. If it is not defined yet, create it with YaST › System › Network Settings › Add › Bridge.

   

   Note: Mappings of Network Devices

   Network devices on the source Xen host can be mapped during the conversion process to corresponding network devices on the KVM target host. For example, the Xen bridge br0 can be mapped to the KVM network default. Sample mappings can be found in /etc/virt-v2v.conf. To enable these mappings, modify the XML rule as necessary and ensure the section is not commented out with <!-- and --> markers. For example:

    <network type='bridge' name='br0'>
      <network type='network' name='default'/>
    </network>

   

   Tip: No Network Bridge

   If there is no network bridge available, Virtual Machine Manager can optionally create it.

virt-v2v has the following basic command syntax:

virt-v2v -i INPUT_METHOD -os STORAGE_POOL SOURCE_VM

input_method

There are two input methods: libvirt or libvirtxml. See the SOURCE_VM parameter for more information.

storage_pool

The storage pool you already prepared for the target virtual machine.

source_vm

The source virtual machine to convert. It depends on the INPUT_METHOD parameter: For libvirt, specify the name of a libvirt domain. For libvirtxml, specify the path to an XML file containing a libvirt domain specification.

Note: Conversion Time

Conversion of a virtual machine takes a lot of system resources, mainly for copying the whole disk image for a virtual machine. Converting a single virtual machine typically takes up to 10 minutes, although virtual machines using very large disk images can take much longer.

1.4.1 Conversion Based on the libvirt XML Description File #

 

This section describes how to convert a local Xen virtual machine using the libvirt XML configuration file. This method is suitable if the host is already running the KVM hypervisor. Make sure that the libvirt XML file of the source virtual machine, and the libvirt storage pool referenced from it are available on the local host.

1. Obtain the libvirt XML description of the source virtual machine.

   

   Tip: Obtaining the XML Files

   To obtain the libvirt XML files of the source virtual machine, you must run the host OS under the Xen kernel. If you already rebooted the host to the KVM-enabled environment, reboot back to the Xen kernel, dump the libvirt XML file, and then reboot back to the KVM environment.

   First identify the source virtual machine under virsh:

   # virsh list
    Id    Name                           State
   ----------------------------------------------------
   [...]
     2     sles12_xen                     running
   [...]

   sles12_xen is the source virtual machine to convert. Now export its XML and save it to sles12_xen.xml:

   # virsh dumpxml sles12_xen > sles12_xen.xml

2. Verify all disk image paths are correct from the KVM host's perspective. This is not a problem when converting on one machine, but may require manual changes when converting using an XML dump from another host.

   <source file='/var/lib/libvirt/images/XenPool/SLES.qcow2'/>

   

   Tip: Copying Images

   To avoid copying an image twice, manually copy the disk image(s) directly to the libvirt storage pool. Update the source file entries in the XML description file. The virt-v2v process will detect the existing disks and convert them in place.

3. Run virt-v2v to convert to KVM virtual machine:

   # virt-v2v sles12_xen.xml1 \
   -i LIBVIRTXML2 \
   -os remote_host.example.com:/exported_dir3 \
   --bridge br04 \
   -on sles12_kvm5

   1	The XML description of the source Xen-based virtual machine.
   2	virt-v2v will read the information about the source virtual machine form a libvirt XML file.
   3	Storage pool where the target virtual machine disk image will be placed. In this example, the image will be placed on an NFS share /exported_dir on the remote_host.example.com server.
   4	The target KVM-based virtual machine will use the network bridge br0 on the host.
   5	The target virtual machine will be renamed to sles12_kvm to prevent name collision with the existing virtual machine of the same name.

1.4.2 Conversion Based on the libvirt Domain Name #

 

This method is useful if you are still running libvirt under Xen, and plan to reboot to the KVM hypervisor later.

1. Find the libvirt domain name of the virtual machine you want to convert.

   # virsh list
    Id    Name                           State
   ----------------------------------------------------
   [...]
     2     sles12_xen                     running
   [...]

   sles12_xen is the source virtual machine to convert.

2. Run virt-v2v to convert to KVM virtual machine:

   # virt-v2v sles12_xen1 \
   -i libvirt2 \
   -os storage_pool3 \
   --network eth04 \
   -of qcow25 \
   -oa sparce6 \
   -on sles12_kvm

   1	The domain name of the Xen-based virtual machine.
   2	virt-v2v will read the information about the source virtual machine directly from the active libvirt connection.
   3	The target disk image will be placed in a local libvirt storage pool.
   4	All guest bridges (or networks) will be connected to a locally managed network.
   5	Format for the disk image of the target virtual machine. Supported options are raw or qcow2.
   6	If the converted guest disk space will be sparse or preallocated.

1.4.3 Converting a Remote Xen Virtual Machine #

 

This method is useful if you need to convert a Xen virtual machine running on a remote host. As virt-v2v connects to the remote host via ssh, ensure that SSH service is running on the host.

Note: Passwordless SSH Access

Starting with SLES 12 SP2, virt-v2v requires a passwordless SSH connection to the remote host. This means a connection using an SSH key added to the ssh-agent. See man ssh-keygen and man ssh-add for more details on this. More information is also available at Chapter 22, Securing network operations with OpenSSH.

To connect to a remote libvirt connection, construct a valid connection URI relevant for your remote host. In the following example, the remote host name is remote_host.example.com, and the user name for the connection is root. The connection URI then looks as follows:

xen+ssh://root@remote_host.example.com/

For more information on libvirt connection URIs, see https://libvirt.org/uri.html.

1. Find the libvirt domain name of the remote virtual machine you want to convert.

   # virsh -c xen+ssh://root@remote_host.example.com/ list
    Id    Name                           State
   ----------------------------------------------------
     1     sles12_xen                     running
   [...]

   sles12_xen is the source virtual machine to convert.

2. The virt-v2v command for the remote connection looks like this:

   # virt-v2v sles12_xen \
   -i libvirt \
   -ic xen+ssh://root@remote_host.example.com/ \
   -os local_storage_pool \
   --bridge br0

1.5 Running Converted Virtual Machines #

 

After virt-v2v completes successfully, a new libvirt domain will be created with the name specified with the -on option. If you did not specify -on, the same name as the source virtual machine will be used. The new guest can be managed with standard libvirt tools, such as virsh or Virtual Machine Manager.

Tip: Rebooting the Machine

If you completed the conversion under Xen as described in Section 1.4.2, “Conversion Based on the libvirt Domain Name”, you may need to reboot the host machine and boot with the non-Xen kernel.

For more information on libvirt, see https://libvirt.org.

You can find more details on libvirt XML format at https://libvirt.org/formatdomain.html.

For more information on virtualization with Xen and KVM, see the SUSE Linux Enterprise Server documentation at https://documentation.suse.com/.

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