[libvirt] QEMU snapshots on ZFS

[Eric Blake]

On 07/04/2014 10:52 AM, Arunas Ruksnaitis wrote:

> Now I am starting to move forward, and have discovered that snapshot is
> only supported as QEMU native "savevm" command, which only works on QCOW2
> backing image.

That's not the only supported snapshot; we also support creating
external snapshots (qemu 'blockdev-snapshot-sync').  And as of qemu 2.1
and libvirt 1.2.7 (both due out at the end of this month), it should be
possible to take an external snapshot to go from 'file (r/w)' to 'file
(r/o) <- temporary (r/w)' , then use your ZFS native commands to do
whatever you want with the read-only 'file', then do an active commit to
go back to 'file (r/w)'.

> 
> Is there any chance to include support for ZFS native snapshots? I.e. do a
> coordinated RAM snapshot in a separate file, snapshot ZFS volume and tie
> these two together in a snapshot XML file.

Sure, patches are welcome.  People have also asked for native LFS volume
snapshot integration; the concept is the same - someone would need to
submit the patch that coordinates the third-party snapshots to happen at
a point while qemu is temporarily using a qcow2 wrapper around the file,
then active commit the temporary wrapper back into the main file once
the third-party snapshot is done.

> 
> A related, but different question: any chance to support ZFS-backed storage
> pools, so that ZFS volumes could be created, and not QCOW images in ZFS
> file system (this is a waste of ZFS, as ZFS already has native COW,
> snapshots, cloning, migration and much more). Should I start a separate
> thread for this topic?

Patches are welcome; you can use existing storage pool code as a
starting point on what needs to happen.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 604 bytes
Desc: OpenPGP digital signature
URL: <http://listman.redhat.com/archives/libvir-list/attachments/20140707/4c6fab2f/attachment-0001.sig>