Re: Win2003 disk corruption with kvm-1.0. and virtio

[Jorge Armando Medina <jmedina@e-compugraf.com>]

On 12/03/13 09:48, Sylvain Bauza wrote:
> Long lasting bug and huge update, but I think I got the root cause.
> FYI, Windows 2003 is having a write cache enabled by default on disk
> drivers. Even with virtio (see driver details, policies).

Hi there,

That option did you use in driver policy?

Thanks


>
> As a consequence, any DLL which is open could be corrupted if we try a
> simple 'qemu-img convert' against the VM.
> The proper way to do a live snapshot is to disable the writecache (and
> goodbye good perfs!) and do the convert.
> The other way is to stop the VM, perform a 'qemu-img snapshot', then
> convert the snapshot.
>
> Hope it can help other people.
> -Sylvain
>
>
> Le 14/02/2013 11:11, Sylvain Bauza a écrit :
>> Interesting point you mention. Even if qcow2 is read only, the image
>> is changing (especially, I'm running IIS with ASP support and VB
>> DLLs) while the snapshot is taken.
>>
>> As asked in a second post, I'm running with latest Windows virtio
>> drivers, but I only apply a virtio driver update *after* running an
>> instance, not before taking the snapshot.
>>
>> What I'll try : run an instance, update the driver, stop the
>> instance, do a qemu-img convert once the instance is stopped.
>>
>>
>> Le 14/02/2013 09:15, Stefan Hajnoczi a écrit :
>>> On Wed, Feb 13, 2013 at 10:53:14AM +0100, Sylvain Bauza wrote:
>>>> As per documentation, Nova (Openstack Compute layer) is doing a
>>>> 'qemu-img convert -s' against a running instance.
>>>> http://docs.openstack.org/trunk/openstack-compute/admin/content/creating-images-from-running-instances.html
>>>>
>>> That command will not corrupt the running instance because it opens the
>>> image read-only.
>>>
>>> It is possible that the new image is corrupted since qemu-img is
>>> reading
>>> from a qcow2 file that is changing underneath it.  However, the chance
>>> is small as long as the snapshot isn't deleted while qemu-img
>>> convert is
>>> running.
>>>
>>> So this doesn't sound like the cause of the problems you are seeing.
>>>
>>> Stefan
>>
>
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