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

[Alexandre DERUMIER]

>>Using snapshot capabilities of the underlying storage is a good idea.
>>LVM snapshots have been used with KVM for a long time. The same works
>>for zfs, btrfs, etc. They are probably more efficient than using
>>QEMU's external snapshots, which must copy data between image files
>>when flattening the image chain.
Yes, indeed ;)  But I'll try to add feature to proxmox for all kind of storage.



>>It should work if you shut down the guest before manipulating snapshots. 
Oh, sorry, I have redone test with stopping the vm before manipulate, and it's 
work fine now.

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.

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 ?

Thanks Again,

Alexandre Derumier
----- Mail original -----

De: "Stefan Hajnoczi" <address@hidden>
À: "Alexandre DERUMIER" <address@hidden>
Cc: "Jeff Cody" <address@hidden>, "qemu-devel" <address@hidden>
Envoyé: Dimanche 26 Août 2012 09:07:44
Objet: Re: [Qemu-devel] qcow2: online snasphots : internal vs external ?

On Sat, Aug 25, 2012 at 6:06 PM, Alexandre DERUMIER <address@hidden> wrote:
> I work since many years with snapshot on zfs or netapp,
> and on these system like ceph, I can rollback at the time of the snapshot, 
> and have a view of when the snapshot was taken.
>
> exemple :
> image1 : empty dir /
> take a snapshot (snap1)
> touch /file1
> now rollback to snap1
> ls / ->empty dir, like when snap1 was taken

Using snapshot capabilities of the underlying storage is a good idea.
LVM snapshots have been used with KVM for a long time. The same works
for zfs, btrfs, etc. They are probably more efficient than using
QEMU's external snapshots, which must copy data between image files
when flattening the image chain.

> now,example with qemu:
> image1 : empty dir /

Did you shut down the guest here?

> take a snapshot: (qemu-img snapshot -c snap1 image1)
> touch /file1

Did you shut down the guest here?

> now rollback to snap1 (qemu-img snapshot -a snap1 image1)
> ls /file1
>
>
> the behaviour is completly different. Did I miss something ?

It should work if you shut down the guest before manipulating snapshots.

Stefan



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Alexandre D e rumier

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