Migrating Virtual Machines

A running virtual machine can be migrated from its source virtual machine host to another virtual machine host. This functionality is referred to as live migration. For live migration to work, the virtual machine being migrated must have access to its storage in exactly the same location on both source and destination host platforms.

Live migration only works when every entity involved is the same architecture. For example, a 64-bit paravirtualized guest running on a 64-bit hypervisor can be migrated a host running a 64-bit hypervisor. If any of the pieces do not match exactly, migration will fail.

Another requirement is, that the involved filesystems are available on both machines. The options to accomplish this task include Network Block Devices (NBD), iSCSI, NFS, drbd and fiber channel devices. Furthermore, the routing of the network connection to the virtual network device must be correct.

The following xend options, which are located in the /etc/xen/xend-config.sxp file, need to be set on both hosts in order for live migration to work.

(xend-relocation-server yes)
(xend-relocation-port 8002)
(xend-relocation-address ")
(xend-relocation-hosts-allow ")

For information on modifying xend settings, see Section 4.2, “Controlling the Host by Modifying xend Settings”.