Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!lll-winken!arisia!sgi!shinobu!odin!anchor!olson
From: olson@anchor.sgi.com (Dave Olson)
Newsgroups: comp.periphs
Subject: Re: How many SCSI disks on one ribbon?
Message-ID: <566@odin.SGI.COM>
Date: 18 Sep 89 01:45:59 GMT
References: <11920@cit-vax.Caltech.Edu>
Sender: news@odin.SGI.COM
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tim@cit-vax.Caltech.Edu (Timothy L. Kay) writes:
>I am hooking some Newbury drives to an Iris 80GTB, and I am running
>into just a bit of trouble.  When I have four 380 MB drives hooked
>up, everything works great.  If I hook up a fifth, I am overloading
>the bus somehow, I think.  When it boots, I get the message

>  unexpected transfer phase: state=4b phase=20
>  resetting scsi: hardware error
The most likely problem here is a SCSI bus problem.  Check to be
sure that ONLY the drive furthest from the CPU is terminated,
that stubs off the main ribbon cable are no more than 4" long,
that the overall cable length is less than 20 feet (including
cabling inside the driver tower, and cabling from the CPU
board to the tower).

Finally, if all these are OK, if your system is more than about
6 months old, you are probably out of luck unless you want
to spend the bucks to upgrade to a new power supply/drive stack.
A number of the earlier 4D machines were cabled in violation of
the SCSI spec, and changes made in manufacturing made it progessively
worse.  You are lucky to get as many as 4 drives working reliably
if this is your problem...

	Dave Olson

It's important to keep an open mind, but not so open
that your brains fall out. -- Stephen A. Kallis, Jr.