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

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

> > Try adding 'sync' after both steps and see if that changes performance.
>
> I did, see "Note 3" in the wiki. It's actually XFS, that caches things
> on amd64, so with sync, the XFS takes 3.5s on amd64 (instead of those
> 0.5s). But ext3 with sync is still very fast (from 0.2s to 0.4s)
> everywhere. So this only makes things worse for XFS...


We just discovered, that mounting XFS partition with:

sudo mount -o nobarrier /dev/sda2 /mnt/p1

speeds things up on all machines. The reason is, that the option "-o
barrier" was added by default to all kernels >= 2.6.17, so dakol has
nobarrier, all the others have barrier. By mounting with nobarrier,
the cp and rm times are 5s on the first run and around 1.7s on
subsequent runs. That's much better for XFS.

Ondrej