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

["Ondrej Certik" <ondrej@certik.cz>]

Hi,

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

and those are the ones I tested. So it's a benchmarking of creating a
tree of hardlinks and then deleting it. For details see that page [1].

If you use cowbuilder, which filesystem are you using? And how long
does it take to copy the COW dir for you?

Ondrej

P.S. I don't know if this belongs to mentors or devel, so I am posting to both.

[1] http://wiki.debian.org/cowbuilder_benchmark