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Date: Wed, 16 Feb 2011 13:21:52 +0000
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Subject: Re: [Qemu-devel] Re: Comparing New Image Formats: FVD vs. QED
From: Stefan Hajnoczi <stefanha@gmail.com>
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To: Chunqiang Tang <ctang@us.ibm.com>
Cc: qemu-devel@nongnu.org

On Tue, Feb 15, 2011 at 7:45 PM, Chunqiang Tang <ctang@us.ibm.com> wrote:
>> 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.

File creation on a sparse image is currently limited by the fact that
the QED implementation serializes allocating writes.  In earlier QED
patch series I had fine-grained metadata locking so allocating writes
scale better but that lead a regression on another benchmark.  I have
this on my todo list.

This is an implementation-specific limitation and is unrelated to the
file format.  It doesn't tell us about a difference between formats.

Stefan