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5.6 Migrating Xen VM Guest Systems
With Xen it is possible to migrate a VM Guest system from one VM Host Server to
another with almost no service interruption. This could be used for example to move a
busy VM Guest to a VM Host Server that has stronger hardware or is not yet loaded.
Or, if a service of a VM Host Server is required, all VM Guest systems running on this
machine can be migrated to other machines in order to avoid interruption of service.
These are only two examples, many more reasons may apply to your personal situation.
Before starting, some preliminary considerations regarding the VM Host Server should
be taken:
• All VM Host Server systems should use a similar CPU. The frequency is not so
important, but they should be using the same CPU family. To get more information
about the used CPU, see
cat /proc/cpuinfo
.
• All resources that are used by a specific guest system must be available on all in-
volved VM Host Server systems. This means, the network bridges must be in the
same subnet, and all used block devices must exist on both VM Host Server systems.
• Using special features like PCI Pass-Through
may be problematic. Do not
implement these when deploying for an environment that should migrate VM Guest
systems between different VM Host Server systems.
• For fast migrations, a fast network is mandatory. If possible, use GB Ethernet and
fast Switches. Deploying VLAN might also help avoiding collisions.
5.6.1 Configuring Xend for Migrations
To prepare a VM Host Server system for migrating, edit the configuration file
/etc/
xen/xend-config.sxp
. Search for the following lines:
#(xend-relocation-server no)
#(xend-relocation-port 8002)
(xend-relocation-hosts-allow '^localhost$ ^localhost\\.localdomain$')
Change the lines to match the following strings:
Managing a Virtualization Environment 41