Re: [libvirt] [RFC] live migration of VMs with internal snapshots

On Tue, Apr 26, 2016 at 06:26:59AM +0300, Maxim Nestratov wrote: > Hi, > > As far as I understand, currently there is no way to live migrate qemu VMs > that > have internal snapshots, because live migration works via qemu drive > mirroring, > which in turns mirrors only shallow block layer, effectively losing existing > embedded > snapshots. The problem could be fixed if we created an external delta for > all disks with > internal snapshots, live migrate such VMs and then auto merge them back into > original images. That said, I would like to know very much your opinion on > the matter > and would also like to know if this approach is affordable. If so, I or one > of my colleagues > will send a pathset to fix this, otherwise what solution for this problem > you will > recommend? With modern QEMU we do the storage migration using an NBD server that is built-in to QEMU. Now this only knows about disks that are currently attached to the VM. I wonder though if we could simply add all the snapshots to the running VM, but not connect them to any guest device. ie, we'd do blockdev_add, but would *not* do the corresponding device_add. The built-in NBD server would then be able to export them in the same way as the other disks.