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Date: Sun, 13 Mar 2011 12:48:27 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] Re: Strategic decision: COW format
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To: Chunqiang Tang <ctang@us.ibm.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel@nongnu.org, Markus Armbruster <armbru@redhat.com>, Aurelien Jarno <aurelien@aurel32.net>

On 03/12/2011 11:51 PM, Chunqiang Tang wrote:
>
> In short, FVD's internal snapshot achieves the ideal properties of G1-G6,
> by 1) using the reference count table to only track "static" snapshots, 2)
> not keeping the reference count table in memory, 3) not updating the
> on-disk "static" reference count table when the VM runs, and 4)
> efficiently tracking dynamically allocated blocks by piggybacking on FVD's
> other features, i.e., its journal and small one-level lookup table.

Are you assuming snapshots are read-only?

It's not clear to me how this would work with writeable snapshots.  It's 
not clear to me that writeable snapshots are really that important, but 
this is an advantage of having a refcount table.

External snapshots are essentially read-only snapshots so I can 
understand the argument for it.

Regards,

Anthony Liguori

> Regards,
>
> ChunQiang (CQ) Tang
> Homepage: http://www.research.ibm.com/people/c/ctang
>