[Qemu-devel] effect of cluster_size on qcow2 performance during expansion

[Qemu-devel] effect of cluster_size on qcow2 performance during expansion

[PANKAJ RAWAT]

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Hi all

I have been working on the qcow2 image format ,

In theory regarding  cluster size it is written that as the size of cluster
increase performance should increase.



But something surprising happen The performance is degrading as the size of
cluster increased from *64K* to *1M* or *2M*  ( during expansion of qcow2
image)



By expansion i mean that initially qcow2 image is small in size and size
increases when we perform any write operation on it.


Here are the reading taken through fio tool during write operation


*Cluster size : 32K    587Mb/sec (aggrb MB/sec)
*

*
*
*Cluster size : 64K    697Mb/sec** (aggrb MB/sec)*
*
Cluster size : 1M     440Mb/sec*  *(aggrb MB/sec)*

*
*
* Cluster size : 2M     289Mb/sec**  (aggrb MB/sec)*

as in above it can bee seen that the 64k is performing better

can any one tell why ?




-- 
*Pankaj Rawat*

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Re: [Qemu-devel] effect of cluster_size on qcow2 performance during expansion

[Stefan Hajnoczi]

On Thu, Feb 23, 2012 at 8:24 AM, PANKAJ RAWAT <pankajr141@gmail.com> wrote:
> Here are the reading taken through fio tool during write operation
>
>
> Cluster size : 32K    587Mb/sec (aggrb MB/sec)
>
>
> Cluster size : 64K    697Mb/sec (aggrb MB/sec)
>
> Cluster size : 1M     440Mb/sec  (aggrb MB/sec)
>
>
> Cluster size : 2M     289Mb/sec  (aggrb MB/sec)
>
> as in above it can bee seen that the 64k is performing better
>
> can any one tell why ?

Yes.  Please see the other email thread you created on this topic.

Stefan