[libvirt-users] Excluding RAW disk from snapshot

[Eric Blake]

On 08/02/2012 10:21 AM, Trey Dockendorf wrote:
> I have an oVirt engine node that currently runs the system on a qcow2
> based virtual disk, and an NFS export volume on RAW.  I'd like to take
> a snapshot before a somewhat risky upgrade of oVirt and can't with the
> raw image attached.
> 
> Looking at the documentation for the snapshot XML, I created this XML
> file for the snapshot
> 
> <domainsnapshot>
>   <name>20120802</name>
>   <description>oVirt 3.1 upgrade</description>
>   <disks>
>     <disk name='vda' snapshot='yes' />
>     <disk name='vdb' snapshot='no' />
>   </disks>
> </domainsnapshot>
> 
> When I try the snapshot I get this error...
> 
> # virsh snapshot-create dc-vmarchitect dc-vmarchitect_ss.xml
> error: argument unsupported: unable to handle disk requests in snapshot

Try again with:

virsh snapshot-create --disk-only dc-vmarchitect dc-vmarchitect_ss.xml

The --disk-only parameter is essential, as the current code base can
only choose between a system checkpoint (disk state and ram state,
stored internally into required qcow2; takes several seconds and the
guest is paused during the action) or disk-only external (disk state
only, external files, does not require qcow2 at the starting point;
completes very quickly).

I have tested that qemu will support the notion of an external system
checkpoint (disk state and ram state, stored into external files, does
not require qcow2 at the starting point), but have to still write the
patches to actually expose that mode; I still have time to get something
proposed before the 0.10.0 feature freeze, so I'll see what I can do.
This third mode of snapshots would not use the --disk-only flag, and
would take several seconds like the existing system checkpoint but has
the advantage that the guest is running during the bulk of the operation.

> 
> According to the documentation,
> http://libvirt.org/formatsnapshot.html, the disk features should be
> available since 0.9.5.  Is this still missing or have I created an
> invalid XML?

Neither - you just missed the --disk-only flag.

-- 
Eric Blake   eblake at 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: 620 bytes
Desc: OpenPGP digital signature
URL: <http://listman.redhat.com/archives/libvirt-users/attachments/20120802/7e2cbfaa/attachment.sig>