Re: [Qemu-devel] qcow2: online snasphots : internal vs external ?

[Stefan Hajnoczi]

On Sun, Aug 26, 2012 at 10:56 AM, Alexandre DERUMIER
<address@hidden> wrote:
> It is possible to achieve the same behaviour with external snapshot ? (I 
> would like to do it online)
> I don't see how I can rollback to the point of time of the snapshot.

The snapshot only captures the contents of the disk.  Rollback does
not make sense without shutting down the guest.  The OS/file system
would be very confused if the disk contents changed underneath it.

Existing hotplug can be used.  For example, if we have an external
snapshot of a virtio-blk drive, we can use hotplug to remove the
drive, choose the snapshot file and attach it again.  This only works
for "data" drives, the root file system usually cannot be changed
while the guest is running.

You may also wish to look at libvirt for higher level snapshot primitives.

> Also I see that snapshot_blkdev qmp command give in his description:
> "Otherwise the snapshot will be internal! (currently unsupported)."
>
> is Live internal snapshots on the roadmap ?

I'm not aware of anyone working on adding internal snapshot in the
near future.  Patches are welcome.

Stefan