[CentOS] Raid / dual Opteron power issues

Hi All,

I've just started caring for a dual Opteron machine.  It has a 3Ware 
9500S-12 RAID controller, a Tyan S2882G3NR motherboard, 10 IBM 400GB 
disk drives, and a 650 watt power supply.

It has been behaving itself quite nicely until recently.  The poor 
behavior started when I upgraded the OS from CentOS 4.1 (32 bit) to 
Centos 4.1 (x86_64).  When running in uniprocessor mode, the system 
appears to work properly.  However, when running in SMP mode I get a lot 
of SCSI disk errors in /var/log/messages.  I've upgraded the 3w_9xxx 
driver and firmware, but no joy (actually, I did get some joy out of 
recompiling the kernel.  Its been several years since I last compiled a 
kernel and the process has changed for the better).

I've been in contact with 3Ware.  From the error logs I supplied to 
them, it looks like the issue is an insufficient power supply.  Their 
rule of thumb is 300W for the motherboard and 35 W for each disk drive. 
  That means that I would need (at a theoretical minimum) a 650 W power 
supply - which I have.

I only notice the problem in SMP mode, not in uniprocessor mode.  That 
suggests to me that (1) I have a boarderline-sufficient power supply 
that can support one but not two CPUs or (2) there is a problem with the 
combination of Opteron/3Ware 9500S-12 hardware and the x86_64 SMP 
kernel.  I suppose there are even worse possibilities, but I'd rather 
not think about those right now.

What do you think?

Does anyone have any experience with this sort of hardware on x86_64 
kernels?

Does the 3w_9xxx driver work well on a x86_64 machine?

Does anyone have a suggestion as to what capacity power supply I should 
have?

Thank you,
Evan