On Thu, 2016-01-21 at 18:42 +0000, Nir Soffer wrote:

On Thu, Jan 21, 2016 at 2:54 PM, Pavel Gashev 
<p...@acronis.com<mailto:p...@acronis.com>> wrote:

Also there is no option in
oVirt web interface to use COW format on NFS storage domains.



You can
1. create a small disk (1G)
2. create a snapshot
3. extend the disk go the final size

And you have nfs with cow format. The performance difference with one snapshot
should be small.


Yes. And there are other workarounds:
1. Use some block (i.e. iSCSI) storage for creating a thin provisioned disk 
(which is COW) and then move it to required storage.
2. Keep an empty 1G COW disk and copy+resize it when required.
3. Use ovirt-shell for creating disks.

Unfortunately, these are not native ways. These are ways for a hacker. Plain 
user clicks "New" in "Disks" tab and selects "Thin Provision" allocation 
policy. It's hard to explain to users that the simplest and obvious way is 
wrong. I hope it's wrong only for MS NFS.


5. Data corruption happens after 'Auto-generated for Live Storage Migration'
snapshot. So if you rollback the snapshot, you could see absolutely clean
filesystem.



Can you try to create a live-snapshot on MS NFS? It seems that this is the
issue, not live storage migration.


Live snapshots work very well on MS NFS. Creating and deleting works live 
without any issues. I did it many times. Please note that everything before the 
snapshot remains consistent. Data corruption occurs after the snapshot. So only 
non-snapshotted data is corrupted.



Do you have qemu-guest-agent on the vm? Without qemu-guest-agent, file
systems on the guest will no be freezed during the snapshot, which may cause
inconsistent snapshot.


I tried it with and without qemu-guest-agent. It doesn't depend.



Can you reproduce this with virt-manager, or by creating a vm and taking
a snapshot using virsh?


Sorry, I'm not sure how I can reproduce the issue using virsh.




Please file a bug and attach:

- /var/log/vdsm/vdsm.log
- /var/log/messages
- /var/log/sanlock.log
- output of  nfsstat during the test, maybe run it every minute?

Ok, I will collect the logs and fill a bug.

Thanks


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