Migration is the transferal of a running virtual domain from one physical host to another. Red Hat Virtualization supports two varieties of migration—offline and live. Offline migration moves a virtual machine from one host to another by pausing it, transferring its memory, and then resuming it on the host destination. Live migration does the same thing, but does not directly affect the domain. When performing a live migration, the domain continues its usual activities, and from the user perspective is unnoticeable. To initiate a live migration, both hosts must be running Red Hat Virtualization and the xend daemon. The destinations host must have sufficient resources (such as memory capacity) to accommodate the domain bandwidth after the migration. Both the source and destination machines must have the same architecture and virtualization extensions (such as i386-VT, x86-64-VT, x86-64-SVM, etc.) and must be on the same L2 subnet.

When a domain migrates its MAC and IP addresses move with it. Only virtual machines with the same layer-2 network and subnets will successfully migrate. If the destination node is on a different subnet, the administrator must manually configure a suitable EtherIP or IP tunnel in the remote node of domain0. The xend daemon stops the domain and copies the job over to the new node and restarts it. The Red Hat Virtualization RPM does not enable migration from any other host except the localhost (see the /etc/xend-config.sxp file for information). To allow the migration target to accept incoming migration requests from remote hosts, you must modify the target's xen-relocation-hosts-allow parameter. Be sure to carefully restrict which hostsare allowed to migrate, since there is no authentication.

Since these domains have such large file allocations, this process can be time consuming. If you migrate a domain with open network connections, they will be preserved on the host destination, and SSH connections should still function. The default Red Hat Virtualization iptables rules will not permit incoming migration connections. To allow this, you must create explicit iptables rules.

You can use the xm migrate command to perform an offline migration :

xm migrate domain-id <destination domain>

You can use the xm migrate command to perform a live migration

xm  migrate domain-id -l <destination domain>

You may need to reconnect to the domain's console on the new machine. You can use the xm console command to reconnect.