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Date: Thu, 10 Jun 2010 09:27:34 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] Re: KVM call minutes for June 8
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To: Kevin Wolf <kwolf@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>, kvm-devel <kvm@vger.kernel.org>, qemu-devel@nongnu.org, armbru@redhat.com, Luiz Capitulino <lcapitulino@redhat.com>

On 06/10/2010 08:08 AM, Kevin Wolf wrote:
> Am 10.06.2010 14:53, schrieb Anthony Liguori:
>    
>> On 06/10/2010 04:43 AM, Kevin Wolf wrote:
>>      
>>> Huh, why this? Seems I still haven't understood all of qcow2 then... I
>>> always thought that there's just a specific offset where VM state
>>> starts, but no explicit end.
>>>
>>>        
>> A live snapshot can last for a very long time.  What happens if you need
>> to allocate a new block for disk I/O while saving a snapshot?
>>      
> You allocate it, I guess?
>
> Note that VM state must be virtually contiguous, but not necessarily
> physically (virtually = on the virtual hard disk as seen by the guest;
> physically = in the image file). It's just not seen by the guest because
> it's saved at a high offset that is after the end of the real disk
> content, but otherwise it should behave the same as guest data.
>    

I guess you could just start writing and then once your finished, you 
could update the snapshot information.  So yeah, I think your right that 
it's doable with the current format.

Regards,

Anthony Liguori

> Kevin
>