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

[Anthony Liguori]

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