RAID performance problems

[Dimitris]

Hello, i'm using a DELL PowerEdge Expandable RAID controler (PERC 3/DCL,
which is the LSI MegaRAID Elite 1600).

The card is 64bit/66mhz, and its installed in my dual athlon board
(Asus A7M266-D) on one of the 64bit/66mhz slots. All other slots are empty.

The problem is that i get very slow writes. Writes are at 20meg/s and
reads are at 150meg/s. (writes should easily reach 80meg/s)

The system runs two IBM Ultrastar 73LZX 10k rpm 18gig drives as RAID 0 (64k stripe).

The problem first appeared under FreeBSD 5.0-R (haven't tried older versions),
but i installed WindowsXP just in case the problem was specific to fbsd, but
then i got the same performance problem.

The logical array runs with Direct I/O enabled, WriteThrough enabled, and Adaptive read ahead.

Anyone seen similar problems? Suggestions are welcome :)