System hangs displaying "ata4 : DISCONNECT required"

[Guillaume de Vinzelles]

Hello,

I ran into a problem I don't know how to diagnose.
I got a FreeBSD 6.0 box using an Adaptec SATA (fake)RAID 1210SA. Two 250
GB Maxtor hard drives are connected to this card, as a RAID1 mirror, and
the resulting filesystem is correctly mounted and NFS exported.
When the traffic rises on those disks, especially when I copy a big file
(around 700 MB or so) on the exported file system, the system hangs
displaying "ata4 : DISCONNECT required". ata4 is the first SATA controller
on the Adaptec card. The card and the disks are brand new, and the
motherboard is a Tyan Tiger LE (dual Pentium 3).
Do you have any clue, or just maybe a way to analyse this problem ? 
Should I post the dmesg, if that can help ?

Thanks in advance for any advices or clues.

Best Regards,

Guillaume de Vinzelles