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I use Xen and LVM to manage the disks attached to the virtualised machines. The logical volumes reside on a SAN which is connected to the virtualisation server by iSCSI.
If I want to move a VM's logical volume from one SAN to another I currently shutdown the VM, dd the LV to the other SAN, update the VM's config to point to the new location of the LV and boot back up.
This works but the only problem is that the amount of time that the VM is offline is proportional to the amount of data transferring.
What I wondered is if anyone could recommend a better way that minimised this offline period? I wondered if maybe I could take an LV snapshot, migrate that whilst the VM was still online, shutdown, migrate and merge changes/differences on the LV and then startup? This would then make the offline period proportional to the amount of changed data which would be much smaller.
Anyway, I hope that this makes sense and welcome your thoughts, suggestions and questions.
Whilst transferring the snapshot the live LV will obviously be changed by the live VM. Is there some way to then turn off the VM and dd the changes/differences between the LV state and the snapshot state?