According to Oliver Fross:
>
>	This makes any additional drives unusable, which really is a 
>bummer.  Any time I try to talk to them, I get the following error:
>
>disklabel: /dev/rsd4d: Input/output error
>

I know that you said it's not termination BUT - check the
termination ;-)  Check every drive in the chain has the terminators
disabled on it - modern drives are sneaky and it is very easy to leave
the terminator enable link on.  I had this happen to me once - a disk
was terminated in the middle of the chain, everything worked fine
until I added another tape drive.

The other thing to check is that the drive spin up on power up.  If
the drives have a delayed spin up then they may not be up & ready when
the probe comes along.  Normally the amount of delay is dependent on
the scsi id so the higher numbered disks are more likely to not be ready.

-- 
Brett Lymn, Computer Systems Administrator, British Aerospace Australia
===============================================================================
  And the monks would cry unto them, "Keep the bloody noise down!"
  - Mort, Terry Pratchett.