[pve-devel] VM snapshot problem

Alexandre DERUMIER aderumier at odiso.com
Fri Aug 24 13:27:02 CEST 2012

>>If not possible, we need to implement that ourselves. 

I have done, it's very easy with internal snapshots. (qcow2 base)
we can use "qemu-img snapshot" online !

qemu-img snapshot -c snap1 vm-115-disk-12.qcow2
qemu-img snapshot -d snap1 vm-115-disk-12.qcow2

(of course rollback, qemu-img snapshot -a, should be done offline)

so the qmp commands, are only for external snapshots for .raw and .qed

Seem simple to works with internal snasphots in a first time.
(If user want it, they can convert raw file to qcow2)

I know that qemu dev are pushing qcow2 V3 for the coming months, trying to have better performance, near raw performance.

>>I had no time to test that. But qmp need to support that for rdb and sheepdog anyways? 
We don't need qmp for rbd and sheepdog snapshot (we can use rbd and collie command),

----- Mail original ----- 

De: "Dietmar Maurer" <dietmar at proxmox.com> 
À: "Alexandre DERUMIER" <aderumier at odiso.com> 
Cc: pve-devel at pve.proxmox.com 
Envoyé: Vendredi 24 Août 2012 13:15:41 
Objet: RE: VM snapshot problem 

> >>Why not? I thought one can specify that with the qmp command? 
> oh maybe for qcow2 can we use the original file as target ? 

If not possible, we need to implement that ourselves. 

> -> { "execute": "blockdev-snapshot-sync", "arguments": { "device": 
> -> "ide-hd0", 
> "snapshot-file": 
> "/some/place/my-image", 
> "format": "qcow2" } } 
> >>I still think we should use internal snapshots. That live merge/commit 
> >>proposal sound like a bad idea to me. 
> Yes, seem difficult to maintain. 
> Also for rollback, we need use on the snapshot file in the qemu command 
> line file=... 
> >>I just though we can use external snapshots when there is no other way 
> >>to do it. 
> >>We can even disable 'remove snapshot' support for that case (simply do 
> >>not allow to remove intermediate snapshots)? 
> I don't know. When you do a snapshot, the new datas are written in the 
> snapshot file. 
> So,I think we need to merge it if we remove the snapshot. (removing the 
> snapshot is merging it) 

Ah, I see. The whole thing gets really clumsy with external snaphots. So I guess 
we should start with internal snapshots only. 

> Internal snapshot is more easy, as datas are in the file, we only need to 
> "qemu-img snasphot -d" to remove the snapshot. 


> But it is possible online with qmp? 

I had no time to test that. But qmp need to support that for rdb and sheepdog anyways? 




Alexandre D e rumier 

Ingénieur Systèmes et Réseaux 

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Fax : 03 20 68 90 88 

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