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From: roman@sigma.UUCP (Bill Roman)
Newsgroups: net.rumor
Subject: Re: Computer Horror Stories
Message-ID: <610@sigma.UUCP>
Date: Wed, 12-Feb-86 21:35:28 EST
Article-I.D.: sigma.610
Posted: Wed Feb 12 21:35:28 1986
Date-Received: Sat, 15-Feb-86 04:38:41 EST
References: <14700001@hplabsb.UUCP>
Reply-To: roman@sigma.UUCP (Bill Roman)
Organization: Summation, Inc., Woodinville, WA, USA, Earth...
Lines: 33


Some years back I was working at the R & D center of a major
company, developing software on a PDP-11.  Of course we were all
researchers and scientists and too busy to run backups - but our
little machine was right across the hall from the center's main
computer, and every morning at 4 am the night shift operator came
over, booted the dump utility and backed up our disk.  This worked
fine until we had the inevitable disk disaster and lost everything.
No problem, just load the backups... uh, oh.

The dump program was a stand-alone system that bootstrapped itself
from the beginning of the tape.  The tapes all booted successfully,
but the utility couldn't find anything on them.  What had happened
was this: the operator would select the week-old tape to be re-used
for the latest backup and bootstrap the dump program from it, and
immediately dump onto that tape.  The dump program, assuming a fresh
tape had just been mounted, would first write itself to the tape AT
THE CURRENT POSITION, then write directory information and files.
When we went to read the tape, the dump program started by rewinding
the tape, then reading past its boot image.  It then expected the
directory - but it found another image, got confused, and gave up.

One of my co-workers sat at the console for what I remember as
hours, single-stepping the dump program until he found out where it
rewound the tape, so he could patch out the offending code.  I think
he also wrote out the dump procedure for that operator....
-- 
Bill Roman	{ihnp4,decvax,allegra,...}!uw-beaver!tikal!sigma!roman

Summation, Inc.
18702 142nd Ave NE
Woodinville, WA 98072
(206) 486-0991