Strategic decision: COW format (was: [Qemu-devel] Re: Comparing New Image Formats: FVD vs. QED)

[Markus Armbruster]

Kevin Wolf <address@hidden> writes:

> Am 15.02.2011 20:45, schrieb Chunqiang Tang:
>>> Chunqiang Tang/Watson/IBM wrote on 01/28/2011 05:13:27 PM:
>>> As you requested, I set up a wiki page for FVD at 
>> http://wiki.qemu.org/Features/FVD
>>> . It includes a summary of FVD, a detailed specification of FVD, and a 
>>> comparison of the design and performance of FVD and QED. 
>> 
>>> See the figure at http://wiki.qemu.org/Features/FVD/Compare . This 
>> figure 
>>> shows that the file creation throughput of NetApp's PostMark benchmark 
>> under 
>>> FVD is 74.9% to 215% higher than that under QED.
>> 
>> Hi Anthony,
>> 
>> Please let me know if more information is needed. I would appreciate your 
>> feedback and advice on the best way to proceed with FVD. 
>
> Yet another file format with yet another implementation is definitely
> not what we need. We should probably take some of the ideas in FVD and
> consider them for qcow3.

Got an assumption there: that the one COW format we need must be qcow3,
i.e. an evolution of qcow2.  Needs to be justified.  If that discussion
has happened on the list already, I missed it.  If not, it's overdue,
and then we better start it right away.

The choice of COW format will have a significant impact over a long
term.  That makes it a strategic decision.  Such decisions should not be
made purely on short-term considerations.

What are our core requirements for The One COW Format?

What's merely nice to have?

How much of it do we want to have ready for prime time in 0.15?

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