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From: Paolo Bonzini <pbonzini@redhat.com>
Date: Wed, 27 Apr 2011 16:29:41 +0200
Message-ID: <4DB82855.9020301@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 3/8] qed: add support for Copy-on-Read
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To: qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>

On 04/27/2011 03:27 PM, Stefan Hajnoczi wrote:
> From: Anthony Liguori<aliguori@us.ibm.com>
>
> When creating an image using qemu-img, just pass '-o copy_on_read' and then
> whenever QED reads from a backing file, it will write the block to the QED
> file after the read completes ensuring that you only fetch from the backing
> device once.
>
> This is very useful for streaming images over a slow connection.

While having the default in the file is sane, it seems to me that it 
should be overridable at runtime, too.

Paolo