Network/Procedures/Migrate a VM from one Xen host to another

Note: You can only migrate from older or equal xen versions!!! If you try to migrate from newer to older, you will cause your VM to die.

• On the target host, assuming the VM uses shared drbd storage, drbdadm verify mail_disk (or whatever your drbd volume is called in /etc/drbd.d).
• On the target host, watch cat /proc/drbd and watch the little verify bar go across.

You really should wait for that verify to finish. Or, you know, #yolo - but don't go that route.

• On the source, then the destination hosts, drbdadm primary mail_disk to bring the disks dual primary (where mail_disk is your disk id in drbd).
• On the source host, xm migrate --live mail 10.56.0.20 where "mail" is the domain's name and "10.56.0.20" is the host you are migrating to.
• Check the VM to make sure everything is cool.
• On the source host, drbdadm secondary mail_disk to get out of the dual primary situation.

You did it!