Extremely slow HDD write performance with GigaRAID on KNXP

Hello!

I finally got rid of my Soyo Dragon+ Via KT266A board and I had high
hopes I can get rid of all the problems it made but it seems my
problems just got worse with the KNXP

Here is the biggest problem I have at the moment and my setup:

* KNXP with P4 2.4C and 1 GB RAM (2x 512 PC400)
* Silicon Image controller is disabled and nothing attached to it.
* Intel SATA ports have 2 Maxtor 120 GB SATA drives in RAID0 (WinXP is
booting from these, read & write performance is as expected on this
RAID0)
* Intel PATA ports have 4 optical drives attached (all seem to work
ok)
* GigaRAID has a Maxtor 160 GB PATA drive (diamondmax9 with 8mb cache)
attached on the primary port as master. read performance is OK (as
good as it was on the Via board on a Via port previously) but write
performance is *extremely* slow, according to hdtach 2.7 MB/s average
write transfer rate (and I don't think it's wrong it IS that slow).

The GigaRAID has been configured to ATA (takes an eternity to detect
the drive on bootup) and now as RAID with the HD in "normal" mode.
both time it's the same, read performance is OK, write performance is
at 3 MB/s...

Is there any way to resolve this?

BIOS version is F6 btw.