SUMMARY: SCSI TERMINATRS and TIMEOUT ERRORS

From: Paul Woods (woodsp@smtplink.indigo.co.il)
Date: Sat May 13 1995 - 14:50:28 CDT

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My original question was about termination problems on the SCSI bus.

I have a minimum of 4 targets on an 11ft cable (low quality) with three of the
four devices located inside a periph cabinet that is at the end of the 11 foot
cable. I am receiving SCSI timeout errors on most installations. I had slowed
the bus, but this did not always help.

The most common answer (so I did not include any of them) was:

"What, are you nuts, you really don't expect SCSI to meet spec"

I had many that said that a cable length of about 10 feet was a maximum that I
should expect to receive good results on a regular basis. This length should
include ribbon cables and connections.

I guess my final solution will be to ask that the Sparc be re-located to the
front of the machine (closer to the periph. cabinet) so that we can shorten our
length.

Thanks to all that responded. Most of messages are included at the end of this
message.

Paul-

--------------------MESSAGES---------------------------------------

1. Shorten the total cable length if possible. The 6m figure includes
some "effective" capacitance for connectors and internal wiring, etc.
My experience shows that if the external wiring exceeds 3.5m with about
four devices, then things get flaky. FPT terminators help only up to a
point - you might get 4.5m out of it - but they are not a true help for
this situation that you have.

Some people here have markedly improved their scsi chains
by adding a SCSI Sentry terminator from APS (mainly mac
oriented, but hi quality stuff in general). They have
two models: one at $39 with no power supply, which can be
added (60Hz 110-120V) for $19 in case the TERMPWR is too
low at the end of the chain, and the other is newer, at
$79, which includes an international power supply as the
only noticable difference They have an 800 number, but as
this would probably not work for you, I'll look up the
international number too.

Here their contact information:
----------------
APS Technologies
6131 Deramus
PO Box 4987
Kansas City, MO 64120-0087

(800) 325-6316 (toll-free in US)
(816) 920-4109 (toll)
(816) 483-3077 (fax)
----------------

Hope this can be of help.

Dave Johnson
Gradient Technologies, Inc.

believe it or not but, I solved the same problem simply by putting the
tape drive as the last device on the bus (physically).

-JimiX

Jimi Xenidis jimix@sickkids.on.ca
Systems Administrator Phone: 416.813.5728
Research Computing Services Fax: 416.813.5779
The Hospital For Sick Children Pager: 1.416.554.2100

Black Box makes a SCSI repeater that allegedly allows you to extend
a SCSI bus up to 39.4 feet. I haven't tried it.

    Black Box
    P.O. Box 12800
    Pittsburgh, PA 15241
    (412) 746-5500

-- - Nate Itkin - Portland Technology Development, Intel Corporation Aloha, Oregon - E-mail: Nate-Itkin@ptdcs2.intel.com

The first thing to do would be to drop the cable length as much as possible. Using high quality cables doesn't fix the problem if you are using ones that are too long or you use to many. If you are anywhere near the 6m limit, you are way past the reasonable levels that one could expect things to work. The SCSI spec claims a specific cable type which is not what you are using when you go to external shoeboxes. use as short of cables as possible and most of your problems will go away. Replace single drive boxes with dual or bigger, etc.

Next make sure that you don't have termination turned on in the drive, or more than one. This is another common problem. To much termination.

There is a company called APS that sells mainly stuff for MacIntoshes. They have a terminator that works quite well.

-_Gene

Contact Andataco in San Diego, CA. They sell FPTs with every drive subsystem they sell. I'm sure they sell just the FPTs by themselves. I don't have a phone # for them off the top of my head, but try their WWW pages: http://www.andataco.com/

Hope this helps.

Michael K. Peterson TRW Network Services mkp@gumby.sp.trw.com Mail Station R3/1086 Phone: 310.814.6873 One Space Park home: mkp@cerf.net Redondo Beach, CA 90278

FPT, call Artecon they have FPT for both SCSI I, and II connectors and the converters from SCSI I to SCSI II.

Paul,

Try Falcon Systems, 1-800-326-1002. They should give you a good price. If you are outside the US, you can e-mail for info at info@falcons.com.

Good luck,

David

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