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Date: Wed, 08 Sep 2010 11:30:10 -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: Christoph Hellwig <hch@lst.de>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel@nongnu.org, Alexander Graf <agraf@suse.de>, Avi Kivity <avi@redhat.com>

On 09/08/2010 10:38 AM, Christoph Hellwig wrote:
> On Wed, Sep 08, 2010 at 12:15:13PM +0100, Stefan Hajnoczi wrote:
>    
>> In-place writes overwrite old data in the image file.  They do not
>> allocate new clusters or update any metadata.  This is why write
>> performance is comparable to raw in the long run.
>>      
> Only if qed doesn't cause additional fragmentation.  Which it currently
> does.
>    

http://wiki.qemu.org/Features/QED/OnlineDefrag

Is a spec for a very simple approach to online defrag that I hope we can 
implement in the near future.  I think that once we have the mechanisms 
to freeze clusters and to swap clusters, implementing much more 
sophisticated defragmentation algorithms will become easy.

Regards,

Anthony Liguori