Reid Linnemann lreid at
Mon Sep 29 21:43:58 UTC 2008

I've seen a number of people having DMA troubles with SATA disks on 
FreeBSD6 and FreeBSD7, and I'm in the same boat. A while back I posted 
looking for help but none could really be found. Today I finally got to 
the bottom of things (at least so far).

Hardware incompatibility.

According to 
there is an upward compatibility problem between a number of VIA and SiS 
chipsets and SATA300 disks. I happen to have one of those controllers 
(SiS964) and a pair of WD1600AAJS disks, which are SATA300 disks.

I ripped apart my machine, and sure enough I had a jumper on each disk 
labelled 'OPT1', which is documented to force SATA150 operation.

I've since cold booted, warm booted, and booted after a power 
interruption with no READ_DMA timeouts on these disks. I think this 
solved the problem in my case.

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