Non-Sun SCSI disk drives on a Sun 4/110

[Neil Gorsuch]

In article <258 at xermes.UUCP> rob at xermes (Robert A. Schroeder) writes:
>I was planning on adding a Maxtor 760 MB SCSI disk to my 4/110.  However,
>I happened upon some information in the "Hardware READ ME FIRST for the
>Sun 4/110 Systems" that floored me.  It says: 
>	The Small Computer Systems Interface (SCSI) connector on the Sun
>	4100 CPU board installed in your 4/110 system may not adhere
>	completely to the SCSI specification.  Pin 26 on the SCSI connector
>	may be grounded.  Do NOT use non-Sun SCSI disk drives with any Sun
>	4/110 or any 4100 CPU based system.  Use of a SCSI drive not
>	purchased from Sun may result in the damage or destruction of the
>	disk drive/s.

Some Sun workstations have the pin that is reserved for supplying
termination power GROUNDED.  (Amazing how this works out to their
advantage :<).  That means if you have your disk drive supplying it's 5
volts power to that pin, and if the pin is grounded at the Sun, you will
indeed SHORT your disk.  All you have to do is look up the termination
power source jumpers for the Maxtor and do the following:

1.	one of the jumpers will let the appropriate scsi signal (pin 26
	sounds right) supply power to the termination resistors location
	in the Maxtor.  DISCONECT THIS JUMPER.  That way, whether or not you
	use the termination resistors in the Maxtor, you won't be shorting
	anything.  Even with the termination resistors removed, both jumpers
	being left in can still short the disk's 5 volt supply.
2.	If you use the termination resistors in the Maxtor, the other jumper
	will connect the disk drive's 5 volt power supply to the resistors
	when the jumper is installed.  As long as the other jumper is removed,
	it is safe to install this jumper in any case.

You should receive a manual with the drive which will explain these
matters in detail (we usually ship manuals with the drives we sell :<).
Here is a kludgy diagram, with most of the SCSI signals removed:

SCSI TERMINATION             JUMPER                 JUMPER        DISK'S
POWER PIN------------------o   TO   o--------------o  TO  o-------5 VOLT
(GROUNDED IN                 REMOVE         |       LEAVE         SUPPLY
SOME SUN'S)                                 |
                                            |
                                             \
             TO     -----------------------  /
           VARIOUS  ----------------------  /  TERMINATION RESISTOR
          SCSI PINS ---------------------  \   PACKS (LEAVE IN IF THIS
                                            \  IS THE LAST SCSI DEVICE)
                                            |
                                            |
                                            |
                                         GROUND

>Is this for real??  I've given my salesman over a week to try to
>confirm/deny this statement and have yet to hear from him.  So, I thought
>I'd turn to netland for some help on this one.   Please tell me it's a
>joke (I've actually already ordered the disk :( ).

It's no joke, you can short you disk if you don't know what you are doing,
and if you assume that Sun ALWAYS provides completely "open systems"
compatible equipment.  It may possibly have been an honest mistake on
Sun's part, but I find it hard to believe that they forgot to check
the SCSI interface standard.

Neil Gorsuch
Uninet Peripherals
neil at cpd.com
uunet!zardoz!neil
(800) 433-6784 outside California
(714) 546-1100 inside California