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Date: Mon, 13 Sep 2010 08:07:53 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format
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To: Kevin Wolf <kwolf@redhat.com>
Cc: qemu-devel@nongnu.org, Avi Kivity <avi@redhat.com>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

On 09/13/2010 06:03 AM, Kevin Wolf wrote:
>
> The real reason why it's not the same story is that a qcow3 would be
> backwards compatible. Old images would just work as qcow3 by changing
> the version number in the header. Even if they are on a block device.
> Even if they are encrypted. Even if they are compressed. Even if they
> have internal snapshots.
>    

I think that's really the point of QED.  I think the features of qcow2 
make it prohibitively difficult to achieve correctness and good peformance.

> We would have just one driver instead of two, and we could tell people
> the upgrade their images and they didn't have to care about feature loss.
>    

If the features don't work correctly, is it really feature loss?

Regards,

Anthony Liguori

> Kevin
>