Re: [Qemu-devel] Silent filesystem/qcow2 corruptions with qemu-kvm-1.0 and 1.1.1

[Tiziano Müller]

Am Montag, den 15.10.2012, 13:11 +0200 schrieb Kevin Wolf:
> Am 12.10.2012 10:53, schrieb Tiziano Müller:
> > Am Freitag, den 12.10.2012, 10:33 +0200 schrieb Stefan Hajnoczi:
> >> On Thu, Oct 11, 2012 at 03:33:23PM +0200, Tiziano Müller wrote:
> >>> Checking the image using `qemu-img check` then gives something like
> >>> this:
> >>>
> >>> ERROR OFLAG_COPIED: offset=3bc30000 refcount=1
> >>> ERROR offset=c7e331: Cluster is not properly aligned; L2 entry
> >>> corrupted.
> >>
> >> Is any other program accessing the qcow2 image on the host while the VM
> >> is running?
> > 
> >> For example, are you running qemu-img on the image while the VM is
> >> running?
> > 
> > On some VMs we tried to extract filesystem snapshots at runtime:
> > 
> >   qemu-img convert -s snapshot-id original.qcow2 snapshot.qcow2
> > 
> > (yes, that's not consistent, we're switching to external snapshots).
> > But that should open the image read-only, right?
> 
> Yes, in theory that should be harmless and even produce a correct copy
> of the snapshot.

Good to know, thanks.

> 
> > Other operations where the qemu-monitor-commands "savevm" and "delvm". 
> > 
> > Although: we created a new qcow2 and even in that the filesystem got
> > corrupted without any of the above actions. So we're pretty confident
> > that those operations are not the sole cause.
> 
> So no internal snapshots are involved at all with this new image?

No. I just checked again: no internal snapshot are currently present nor
have been added/removed in the past.

>  I'm
> asking because in the past non-reproducible failures were reported with
> snapshots, but I'm not aware of any case that didn't use snapshots.
> 
> Any other non-default feature that you used, like compression?

No, we either create the qcows by hand using:
  qemu-img create -f qcow2 kvm-0XY_01.qcow2 30G

or (usually) using libvirt:
  virsh vol-create $pool $diskfile

where $diskfile points to a xml like this:

<volume>
  <name>${diskfilename}</name>
  <allocation>0</allocation>
  <capacity unit="G">${kvmsize}.qcow2</capacity>
  <target>
    <format type='qcow2'/>
    <permissions>
      <owner>0</owner>
      <group>3000</group>
      <mode>0660</mode>
    </permissions>
  </target>
</volume>

and $pool references a directory-based storage pool.

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