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From: mangler@cit-vax.Caltech.Edu (System Mangler)
Newsgroups: comp.unix.wizards
Subject: Re: SI 9900 hangs
Message-ID: <3321@cit-vax.Caltech.Edu>
Date: Fri, 24-Jul-87 06:00:44 EDT
Article-I.D.: cit-vax.3321
Posted: Fri Jul 24 06:00:44 1987
Date-Received: Sat, 25-Jul-87 12:51:19 EDT
References: <8269@brl-adm.ARPA>
Organization: California Institute of Technology
Lines: 32
Summary: common problem, check the power supply

In article <8269@brl-adm.ARPA>, eichelbe@nadc.arpa (J. Eichelberger) writes:
> Every so often we get a system hang.	All activity on the SI controller
> stops.  Hitting the reset on the toggle switch restarts everything.  Most
> of the time we don't see any error messages.	If we do see one, it's
> hp0: not ready

We get these too.  The last time it happened, I checked the registers,
and all 5 drives had just completed a seek (a sign that the massbus
datapath is marked "busy") and they all had the UNS (unsafe) bit set.

cithex.caltech.edu has the same problem.  They run VMS.

The SI local office says this is a common problem, typically caused
by marginal power supply output.  I've not had the chance to verify
this (there isn't enough downtime on this machine for my purposes).

>   We are using the standard 4.3 BSD hp.c for the driver.

I sure hope that you're using error-free packs.  The error position
determination algorithm in that driver depends on separate counters
for the number of bytes DMA'd and the number of bytes read/written;
but the SI 9900 uses the first counter for both, so on an error, the
driver thinks that more sectors were written than actually were.

(Before you start flaming about SI:  that problem is easy to work
around compared to some of the bugs I've seen in the Emulex SC7000).

Seismo has a version of hp.c that works around this by looking at
the track/sector register (HPDA) instead.  It can still lose data
silently, but if retries are a rare event, it can be lived with.

Don Speck   speck@vlsi.caltech.edu  {ll-xn,rutgers,amdahl}!cit-vax!speck