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.
The other idea would be to just run a standalone qemu-nbd process to
export them, but I think that's a bit more messy because it means we'd
have to manage a bunch more external processes and allocate extra net
connections.
Regards,
Daniel
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