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

[Stefan Hajnoczi <stefanha@gmail.com>]

On Fri, Oct 12, 2012 at 10:53:29AM +0200, Tiziano Müller wrote:
> 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?
> 
> 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.

Okay, that's consistent with the other symptoms you've reported.

It's not clear whether the corruption arises inside qcow2 or if
something else is causing corruption and qcow2/xfs get upset.  That is
the next step to debugging this - hopefully it will become possible to
reproduce it reliably, at which point it is much easier to debug :).

Stefan