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

[Daniel P. Berrange]

On Tue, Apr 26, 2016 at 09:19:44AM +0100, Daniel P. Berrange wrote:
> 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.

Sigh. Ignore this. You're talking internal, not external snapshots.


Regards,
Daniel
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