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Re: [Qemu-devel] Re: Strategic decision: COW format

From: Anthony Liguori
Subject: Re: [Qemu-devel] Re: Strategic decision: COW format
Date: Sun, 13 Mar 2011 12:48:27 -0500
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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.


Anthony Liguori


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

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