SCSI timeouts

[Dan Watts]

Lately I've been getting a few errors like

  sc0,2: Resetting SCSI bus: timeout after 60 sec

These seem to occur randomly and infrequently.  My setup is
a Personal Iris with QIC-24, QIC-150, internal 350MB+ drive
and an external 650MB+ drive.  I don't recall seeeing this
error before I put the external drive on.  All the hardware
works fine otherwise.  I was able to get the error to repeat
itself today by trying to tar some files from the external
drive to a 3M DC615A tape in the QIC-150 drive.  Should I
put my external disk at a lower SCSI address than the tape
drives?

% hinv
12 MHZ IP6 Processor
FPU: MIPS R2010A/R3010 VLSI Floating Point Chip Revision: 1.5
CPU: MIPS R2000A/R3000 Processor Chip Revision: 1.6
Data cache size: 8 Kbytes
Instruction cache size: 16 Kbytes
Main memory size: 8 Mbytes
Graphics board: GR1.2 
Integral Ethernet controller
Integral SCSI controller WD33C93
Disk drive: unit 3 on SCSI controller 0
Disk drive: unit 1 on SCSI controller 0
Tape drive: unit 4 on SCSI controller 0: QIC 24
Tape drive: unit 2 on SCSI controller 0: QIC 150
%
-- 
#####################################################################
# CompuServe: >INTERNET:uunet.UU.NET!ki!dwatts    Dan Watts         #
# UUCP      : ...!uunet!ki!dwatts                 Ki Research, Inc. #
############### New Dimensions In Network Connectivity ##############