Re: speed of COW directory copying: XFS 20x slower than ext3

[Asheesh Laroia <asheesh@asheesh.org>]

On Sun, 16 Sep 2007, Ondrej Certik wrote:

> I am using cowbuilder for building my packages, because the
> initialization takes like 10s, compared to several minutes with
> pbuilder on my system. A few days ago, I realized that on one of my
> systems, it takes 0.5s only to copy the COW directory. I became
> curious and wanted to know why, so I did a benchmarking [1] and to my
> utter surprise, it turned out the problem is in the XFS filesystem,
> that is 20x slower, than the ext3 filesystem. I know that XFS is bad
> at handling small files, but 20x times?
>
> Basically, what cowbuilder is doing is just those 2 commands:
>
> cp -al /var/cache/pbuilder/base.cow /tmp/new
> rm -rf /tmp/new

Does this possibly have to do with buffer flushing choices by the 
filesystem?  Maybe xfs syncs after some operations (like rm -rf) that ext3 
does not.

Try adding 'sync' after both steps and see if that changes performance.

-- Asheesh.

--
  An Irishman is never at peace except when he's fighting.