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On Mar 9, 2012, at 8:51 AM, Daniel P. Berrange wrote:

> On Fri, Mar 09, 2012 at 10:43:35AM -0600, rbabu at hexagrid.com wrote:
>> Even though it's more of a libvirt question since the topic of snapshot
>> is being discussed, thought of asking it. Does libvirt 0.95 uses the
>> backing file concept? or is that the same thing that Vish mentioned 
>> as option 1
> 
> The latest snapshot APIs in libvirt are broadly configurable by passing
> in suitable XML. So if you want to take snapshots on the SAN, or using
> LVM or backing files, they can all be made to fit in with libvirt's
> new APIs. I'm not entirely familiar with how to use it, so if you want
> fine details head over to the libvirt mailing lists where the authors
> of the libvirt snapshot code will be able to assist.

So far my experiments with the newer code in libvirt have been unsuccessful, so we may have to just go with the older version that does a managed save in between.

Using the external snapshot creates a backing file which it seems to be impossible to remove. I can extract the snapshot but attempting to delete it gives me:

libvirtError: unsupported configuration: deletion of 1 external disk snapshots not supported yet

I can't seem to do an internal only snapshot of just the disk.  Doing it while the machine is running gives me:

libvirtError: unsupported configuration: active qemu domains require external disk snapshots; disk vda requested internal

and using managed save first:

libvirtError: unsupported configuration: disk snapshots of inactive domains not implemented yet

Unless there is some magic incantation to allow me to create an external snapshot and then later remove it so I don't leave a chain of backing files around I think we have to go with the compatibility version.