[pve-devel] VM snapshot problem

Alexandre DERUMIER aderumier at odiso.com
Fri Aug 24 11:53:48 CEST 2012


>>I do not see a big problem - why do you think that does not work 
>>for VM snapshot purposes? 

because raw file, is just a flat raw ....no metadatas, no copy on write.
Did I miss something ?


I also see that ibm worked last year on a new format: FVD
http://researcher.watson.ibm.com/researcher/view_project.php?id=1852
http://wiki.qemu.org/Features/FVD

same performance than raw but with snapshot support
I don't know why it's not already in qemu upstream.

>> xen people claim they can do that without support from san/nas. 
For nfs, I really can't see how it's possible. (maybe xen people are crazy :-) Do you have some references mailing list ?)
Vmware use their vaai api, which is integrated in all the big san appliances. But closed source protocol...
Openstack have a netapp (soap) and nexenta (rest) plugin to do this.

>>Yes, but only on one node, and I delete the snapshot afterwards, i.e. we never 
>>move such image while snapshots are active! 
Ah ok. I really can't help you, I never use lvm in cluster.

----- 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 11:25:40 
Objet: RE: VM snapshot problem 

> >>The problem with that is that most users use LVM, NFS or RAW files on 
> local storage. 
> >>So how can we snapshot such images? 
> >> 
> >>For NFS and RAW files we can create and external snapshot (base image + 
> writable image file)? 
> I don't think it's possible. this is main reason why qcow2 exist. 

I do not see a big problem - why do you think that does not work 
for VM snapshot purposes? 

> for nfs,it's possible if you have a san/nas which support snapshot on his 
> filesytem. Like netapp nfs for exemple. (but need to implement snapshot api) 

xen people claim they can do that without support from san/nas. 

> For local raw file, it should be possible with zfs or btrfs. (remote linux nfs 
> storage with zfs,btrfs should work too, implement snasphots via ssh 
> commands) 

sorry, but we can't use any of those file systems for known reasons. 

> (but you can convert raw to qcow2 also) 

I am looking for a solution - not a workaround ;-) 

> I known that qemu developper are currently working for optimize qcow2 
> performance. 
> 
> 
> >> But how can we handle LVM (lvm snapshots on shared storage does not 
> work at all)? 
> I really don't know. 
> for "new" lvm format (dm-thinp) , it doesn't work. 
> For "old" lvm format, maybe. (But I have read some articles with bad 
> performance about it) 
> 
> Don't you use already lvm snapshot for backups ? 

Yes, but only on one node, and I delete the snapshot afterwards, i.e. we never 
move such image while snapshots are active! 




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Alexandre D e rumier 

Ingénieur Systèmes et Réseaux 


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