Re: qemu and qemu.git -> Migration + disk stress introduces qcow2 corruptions

[Juan Quintela <quintela@redhat.com>]

Avi Kivity <avi@redhat.com> wrote:
> On 11/09/2011 07:35 PM, Anthony Liguori wrote:
>> On 11/09/2011 11:02 AM, Avi Kivity wrote:
>>> On 11/09/2011 06:39 PM, Anthony Liguori wrote:
>>>>
>>>> Migration with qcow2 is not a supported feature for 1.0.  Migration is
>>>> only supported with raw images using coherent shared storage[1].
>>>>
>>>> [1] NFS is only coherent with close-to-open which right now is not
>>>> good enough for migration.
>>>
>>> Say what?
>>
>> Due to block format probing, we read at least the first sector of the
>> disk during start up.
>>
>> Strictly going by what NFS guarantees, since we don't open on the
>> destination *after* as close on the source, we aren't guaranteed to
>> see what's written by the source.
>>
>> In practice, because of block format probing, unless we're using
>> cache=none, the first sector can be out of sync with the source on the
>> destination.  If you use cache=none on a Linux client with at least a
>> Linux NFS server, you should be relatively safe.
>>
>
> IMO, this should be a release blocker.  qemu 1.0 only supporting
> migration on enterprise storage?
>
> If we have to delay the release for a month to get it right, we should. 
> Not that I think we have to.

I kind of agree here, but it is not my call.  Patch 1/2 have been used
on RHEL for almost 3 years, so it should be safe (TM).

Later, Juan.