*BSD News Article 95995


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From: Tony Griffiths <tonyg@OntheNet.com.au>
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: NCR SCSI Fatal errors!
Date: Fri, 23 May 1997 19:07:31 +1000
Organization: On the Net (ISP on the Gold Coast, Australia)
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To: "O. Hartmann" <ohartman@ipamzlx.physik.uni-mainz.de>
Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:41490

O. Hartmann wrote:
> 
> Dear Sirs.
> 
> Using FreeBSD 2.2.2 produces a lot of errors when booting.
> I switched these days from FreeBSD 2.1.7.1 to FreeBSD 2.2.2
> and my NCR 53C810 SCSI controler did its work well until the
> switch. Sometimes when I must reboot the system this error
> occurs like ncr0(0:0:0) FATAL ERROR and so on. I think its a
> kernel problem and it should be possible to change some parameter
> to solve this problem.

We here have been using NCR 53C810 SCSI controllers for 18 months with
FreeBSD 2.1.5 -> 2.1.7.1 -> 2.2.1 -> 2.2.2 and I have not had a single
problem (with the controller) on any of the 3 machines that use this
chip.

Where I have had problems is with the SCSI cable(s) and termination.  If
you don't get this right then all sorts of strange things (random bus
hangs for instance) can, and will, happen!

> 
> An other problem occurs with my Wangtek ES5525 tape drive. When
> I made the last backup under FreeBSD 2.1.7.1 all things seemed
> to be clear, now I can not load the backup from tape. The drives
> move shortly forward, then backward, then forward again - like dancing,
> then, after a while, an error occurs like bad block at ...
> What happened to my drive? I think this is maybe a kernelproblem, too.

I think maybe a SCSI cabling/termination problem or a bad tape.  A
friend told me earlier in the week that he had a SCSI tape which just
would not work reliably.  That turned out to be incorrect cabling which
was putting enough "noise" onto the SCSI bus to totally upset the tape
drive.

In this case it was a 1" (2.5cm) 'stub' cable between the drive and the
SCSI cable.  This is _TOTALLY_ illegal as it has transmission line
reflection ramifications causing signals to 'ring' such that devices see
multiple signal transitions when there should be only one.  My guess is
that you have something similar to this or have not terminated the cable
at all, again causing signal reflections and ringing.

Tony