From: donn@carson.u.washington.edu (Donn Cave)
Newsgroups: comp.sys.sequent
Subject: Re: scsi this...
Date: 27 Jul 92 20:15:40 GMT
Distribution: usa
Organization: University of Washington

tony@hacgate.SCG.HAC.COM (Tony Reeves) writes:

| We have a Sequent S81 running the sequent drive controllers running swallow,
| super swallows and NEC drives. 

| We would like to use any standard scsi drives on our system. Is anyone using
| standard scsi drives (like a Maxtor P1-17s?) on a sequent? If so can you use
| any scsi drives? what controller do you use? can you format drives while in
| multi-user mode?

| any answers would be great.

Good, because this answer probably won't be much help to you.  We finally
succeeded in attaching a 3rd party (DEC) SCSI disk drive to our Sequent
2000/750, just this last week, after much head-scratching and fumbling
around.  I'm going to try to summarize what we now know about it, since
several people who were kind enough to respond to my previous inquiry on
the subject expressed some interest.  However, I believe that your S81
doesn't have the hardware that's needed for this.  Ours certainly doesn't.

The SCSI-2 interfaces to our 2000 go through the QCIC controller(s).  We
have one such controller, with 4 ports; port 0 is already occupied with
a "pbay" that drives two 1.2 MB Hewlett Packard SCSI disks.  The pbay
apparently performs some functions that are required by these drives, but
that other vendors may incorporate into their drive boxes.

We plugged our new disk directly into QCIC port 1.  I can't explain the
numbering system, but that makes the disk /dev/qd6.

Of course we had to construct our own VTOC, using information supplied by
the vendor, and when that appeared to be in error we had to write a program
to investigate the disk (I believe we actually modified the mkvtoc program
to find out how many cylinders were actually present).  It turned out that
our VTOC needed to account for one more cylinder than the vendor reports.

Notes:

    1.	SCSI 2 interfaces:  it turns out that there are two kinds of SCSI 2
	interfaces.  "Open-ended", the kind that one generally sees on
	workstation systems like DECstations and RS/6000s, isn't capable
	of handling long cabling distances like the "differential" interface
	that Sequent supports on the 2000.  The disk vendor may be able to
	supply a differential drive, if you ask.

    2.	Cables:  our drives have a Centronix (wide) port, and the 2000's
	QCIC ports have a Honda (narrow) port.  We had to arrange to have
	a special cable made - if you will need one, ask early, because it
	could take a while.

    3.	Support:  Sequent will not be able to help you very effectively in
	attaching 3rd party disks.

We will probably know more about this situation, collectively, when the
man who did most of the work comes back from vacation, and if I can add
anything to this I'll post it.  The short answer seems to be that we now
think that 3rd party SCSI 2 disk drives can be attached to a Sequent 2000
system, but it's not like our other UNIX platforms, DECstations, RS/6000s,
etc., where it's little more than a matter of plugging them in.

	Donn Cave, University Computing Services, University of Washington
	donn@cac.washington.edu