Expireover running really slow

[Kristian Grønfeldt Sørensen]

Hi.

I've set up a new inn server as a replacement for our old one. The
server is running inn 2.4.3-1 from Debian stable.
My problem is that expireover is taking approximately 16 hours to
finish. I find this quite strange as the new server is more powerful
than the old one, which did not have this problem. 

Since the new server has more disk space, there will be more articles
stored in the spool, but the old server can finish expireover within an
hour or so. 

My setup is:

article-spool and overview files is on two separate LVM logical volumes
with XFS on top of them. All articles are stored in a total of 280 CNFS
buffers. 
Overview is buffindexed in a total of 82 files.
The LVM volumes is hosted on a 4-disk RAID-5 array on an Intel SRCS28X
sata controller. Benchmarking with bonnie++ on this device reveals read
speeds of around 140 MB/s and write speeds of around 110 MB/s, so the
underlying hardware should not be any problem.

However during expireover the box spends ~60% if its time in IOWait
mode, which indicates to me that the problem is related to the disk
device.

Using iostat, I can see that constant reading of approximately 1MB/s
and, and almost no write requests. The LV hosting the article spool has
almost no reads but around 1 MB/s but in a very bursty fashion - always
4 MB at a time. 

Does any of you have any ideas for optimizing expireover performance for
this system? I've tried playing around with readahead-policies and
enabling/disabling write caching with no result.

Regarde

Kristian Sørensen