Performance degeneration issues

[Markus Roth]

Hello,

I'm running a Centos 5.4 x64 Server with Raid0 HDDs and XFS.

I did some performance tweaking according to [1] as performance was not good enough with std. options.
Extracting a tar archive with 6.1 million files (avg. Size just below 2KiB) is blazingly fast after the fs has been
generated. But after some time while doing deletes/moves (need to sort those files by their contents) the fs
performance degenerates quite badly (from 8k file writes/sec to about 200).

Is there any way I can find out what the issue is and how I can help it?
(I tried numerous other FSs and of those XFS has left the best impression in my use case)

Tweaks I used:

mkfs.xfs -b size=2048 -l size=64m
mount -o noatime,nodiratime,logbufs=8

I tried playing with the log size and logbufs, but to no avail. I would be thankful if you could give me some 
pointers as I have spent the last 3 weeks fiddling with filesystem etc..

Thanks and Greets from Germany,
Markus Roth

[1] http://everything2.com/index.pl?node_id=1479435