Disk or SCSI controller failure

-- 
Hi:
I have a DEC AlphaStation 500/400 runing Tru64 4.0E.I am trying to determine if 
I have a disk or SCSI controller failure. Here is the background:
 A couple days ago the machine stopped responding via telnet. I went to the 
machine to find the following messages on the console log:
Deferring I/O errno 5 for block (0x75aa0,0x75aa0 on device 8,17414
Deferring I?O errno 1 for block (0x400x40) on device 817408
Shortly after seeing this message I started hearing a clicking noise and noted 
the scsi activitly light was on. It also sounded like it was also trying to 
read from one of the disks.
I ended up halting the machine and trying to boot from a CD. I received the 
following from the console prompt (>>>):
...
jumping to bootstrap code (scsi activity light was on)
contig-malloc: not enough aligned node memory
pmr0: 95 contiguous pages available
panic (cpu0): contig-malloc of in-memory sg table failed
Dump No primary swap no explicit dumpdev
halted CPU0 
halt code5
I then tried to boot from the root disk. It sounded like the disk were spinning 
up but then stoped and restarted continously. The only thing I could do was to  
halt the machine to get back to the  console prompt.
Also all the devices show up if I try the "show device" command--including the 
SCSI controllers.
So it probably is the disk(s) that have crashed but how can I verify this. And 
if it is indeed the disks, any suggestions on where I can purchase another?
Thanks for your help 
Wayne