SATA write performance problems (on HP MicroServer)

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

I have performance problems writing to the SATA discs on my HP MicroServer.
In the BIOS, IDE is switched to AHCI. The discs do NOT have 4k sectors.
I can read more than 70MB/s.

I can write 110 to 120 transfers per second regardless of block size.
With 64k blocks, that's 6.7MB/s. If I use 32k blocks, it's 3.6MB/s, on 16k 
blocks 1.9MB/s and so on.
I ruled out alignment problems by moving the test partition, one block at a 
time, seven times. No difference.

Any ideas? Anyone with a HP MicroServer to verify?