VIA VT8251 low performance (was: ASUS A8V-MX)

["Zrin" <zrin.it@ziborski.net>]

[...]
> ata1: SATA link up 3.0 Gbps (SStatus 123 SControl 300)

this sounds promising ...

[...]
> >> dd if=/dev/zero of=/tmp/test.dat bs=1M count=2048
> 
> 1115684864 bytes (1.1 GB) copied, 44.5009 seconds, 25.1 MB/s
> 
> 
> >> dd of=/dev/null if=/tmp/test.dat bs=1M count=2048
> 
> 1115684864 bytes (1.1 GB) copied, 52.1885 seconds, 21.4 MB/s

but this is totally dissapointing. I'm getting about
60 MB/s with these simple tests (Asus A8V-VM).
I was expecting SATA II to bring at least 150 MB/s.

On VT8237 (Asus A7V880, AMD K7) I'm getting in average
over 80 MB/s.
When reading from RAID0 it gets over 150 MB/s. SATA I.

There is something wrong, either with this south bridge or
with the driver...

@Raghavendra: Thank you very much for your answers!

Zrin