On Thu, Jan 21, 2016 at 10:13 PM, Pavel Gashev <p...@acronis.com> wrote:
> 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> 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.

Sure I agree.

I think we do not use qcow format on file storage since there is no
need for this,
the file system is always sparse. I guess we did not plan to use MS NFS.

I would open bug for supporting qcow format on file storage. If this works for
some users, I think this is an option that should be possible in the
ui. Hopefully
there are no too many assumptions in the code about this.

Allon, do you see any reason not to support this for user that need this option?

> 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.

live migration starts by creating a snapshot, then copying the disks to the new
storage, and then mirroring the active layer so both the old and the
new disks are
the same. Finally we switch to the new disk, and delete the old disk.

So probably the issue is in the mirroring step. This is most likely a
qemu issue.

> 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.

I'll try to get instructions for this from libvirt developers. If this
happen with
libvirt alone, this is a libvirt or qemu bug, and there is little we (ovirt) can
do about it.

> 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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