Read / write timeouts on SATA disks connected to ICH9

[Pieter de Boer]

Hi list,

I'm running FreeBSD 8.0-RELEASE-p1 on a Dell R300 which has a ICH9 SATA 
controller on-board (do not have the RAID controller).

The system has 2 disks in a gmirror setup. Every now and then, probably 
under some load, one of the disks gets read or write timeouts like:
May  5 03:01:37 aberdeen kernel: ad4: timeout waiting to issue command
May  5 03:01:37 aberdeen kernel: ad4: error issuing WRITE_DMA48 command
May  5 03:01:37 aberdeen kernel: GEOM_MIRROR: Request failed (error=5). 
ad4[WRITE(offset=200404975104, length=16384)]
May  5 03:01:37 aberdeen kernel: GEOM_MIRROR: Device gm0: provider ad4 
disconnected.

or:

May 13 14:41:26 aberdeen kernel: ad6: TIMEOUT - READ_DMA48 retrying (1 
retry left) LBA=975513887

Sometimes the read/write succeeds after a few retries, but sometimes it 
does not, so geom_mirror throws the disk out of the mirror.

Tonight ad6 was thrown out of the mirror and ad4 then gave actual read 
errors, resulting in a big mess :(

My question: does anyone have experience with FreeBSD on a Dell R300 or 
can anyone give me some help in trying to fix the timeouts?

I was told using AHCI could be better for SATA disks, but apparently 
(http://permalink.gmane.org/gmane.linux.kernel.pci/8267) the BIOS does 
not support turning that on, so that does not appear to be an option.

Thanks,
Pieter