I will do the tests with another drive (from WD) today. But I've
fogot to say that I have another S8005 m/b with SP5100 that working
perfectly with these particular Hitachi drives (please see boot log
for it in dmesg-good at the same URL). So the problem can be in init
procedure for AMD south bridge or SATA controller. The differences
between m/b is very little - working has onboard audio, not working
hasn't. The diff in boot log is present too in file diff.txt

quoted

 I'm observing the problem with AMD SP5100 SATA controller. The
problem appears as very low (2-3MB/s) write perfomance. Reading drops
too, but not such dramatically (from 100Mb/s on other hardware to
50-60Mb/s on SP5100). This problem is checked on several kernels
(2.6.x, 3.2.x, 3.4.x) including latest 3.5 and with all possible SATA
BIOS settings. The hardware is Tyan S8005 m/b (latest BIOS v1.03), AMD
X6 1045T, 8GB ECC memory and Hitachi HTS725050A7E630 drive.  Moreover
- I've checked 2 different identical boxes - it is 100% reproducable
on both.

Have you tried doing the same test on the same mobo but with another
drive, possibly by another manufacturer? Do you see the same write
slowdown with the second drive too?

Thanks.

--
Regards/Gruss,
    Boris.

-- 
Rus