[Xen-devel] QEMU qcow2 snapshotting (was Xen 4.2.1 live migration with qemu device model)

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 11 Dec 2012, Alex Bligh wrote:
> --On 11 December 2012 19:24:54 +0000 Stefano Stabellini 
> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> 
> > It would be great if you could implement QEMU qcow2 snapshotting support
> > in libxl, so that everything can happen seamlessly using a variation of xl
> > save/restore.
> 
> I'd guess that isn't hard. We already have QEMU qcow2 snapshotting support
> on qemu-xen working via direct calls to QEMU - I think it 'worked just like
> kvm'. I seem to remember there is some fiddling to do with an open fd number
> in qemu for the live rebase, and some limitations (for instance I couldn't
> see how to do a consistent snapshot of the same device presented both pv
> and emulated under HVM - which is theoretically an issue if you have
> one partition mounted one way and one the other).

It shouldn't be hard: we already have pretty good QMP support in libxl,
so it should be just a matter of plumbing through the new commands.

QEMU supports both internal and external snapshots, but I think that the
internal ones are more interesting (snapshot saved within the qcow2
file), which ones are you using?

Also QEMU's snapshots support both disk and/or the entire VM state
(savevm vs. snapshot_blkdev): one thing that would be cool is if we
could save the Xen VM state (AKA xl save) within the snapshot in the
qcow2 image. Basically we are talking about a new pair of xl
save/restore commands (or maybe options to the existing save/restore
commands) that make use of QEMU qcow2 snapshots as storage for both the
disk delta and the VM state.
To do this we would probably need a new QEMU QMP command, but I think
that it would be very useful.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel