aacraid drops offline w/ opteron and 16G of RAM (2.6.9)

I'm using an Adaptec 2200S RAID card in an opteron system. It works fine if I use 12G of RAM but if I have 16G it drops offline under stress (bonnie++ etc). Basically it's as if the whole array has been removed.

I first saw this problem under the suse9.1 2.6.5 kernel but the problem is still
there under the 2.6.9 kernel as well.

I've tested the hardware, and this has happenned on 2 seperate systems so it's not a hardware component problem.

Based on history with different RAID cards, I tried turning off node interleave and harddware IOMMU on the Arima motherboard, but that hasn't made a difference.

Has anyone seen this problem before?

regards,
dan carpenter