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From: bobg@rains.wpd.sgi.com (Bob Green)
Newsgroups: comp.sys.sgi
Subject: Re:  Bad tapes again!!!!
Message-ID: <1990Sep21.201851.2786@odin.corp.sgi.com>
Date: 21 Sep 90 20:18:51 GMT
References: <9009192232.AA23148@mcirps2.med.nyu.edu>
Sender: news@odin.corp.sgi.com (Net News)
Reply-To: bobg@rains.wpd.sgi.com (Bob Green)
Organization: sgi
Lines: 35

In article <9009192232.AA23148@mcirps2.med.nyu.edu>, karron@MCIRPS2.MED.NYU.EDU writes:
|> I too have had bad tapes from sgi. I usually end up getting a new tape from
|> them. Still, don't they try to re-read the tapes, or otherwise verify tapes
|>  after they make a copy ?
|> 
|> dan.
|> +-----------------------------------------------------------------------------+
|> | karron@nyu.edu                          Dan Karron                          |
|> | . . . . . . . . . . . . . .             New York University Medical Center  |
|> | 560 First Avenue           \ \    Pager <1> (212) 397 9330                  |
|> | New York, New York 10016    \**\        <2> 10896   <3> <your-number-here>  |
|> | (212) 340 5210               \**\__________________________________________ |
|> +-----------------------------------------------------------------------------+

Each tape that is produced by SGI or its vendors is rewound and read for data consistency.
On a sampled basis tapes are moved from one drive to another to verify tape drive head
alignment.  Our current research shows one cause above all others in contributing to
tape read errors.  We have found that foreign material on the tape drive heads will increase
the probability of read errors.  In most cases this results in recoverable errors which just slow
the read process.  In a few cases it results in unrecoverable tape read errors.  The solution in all cases
is to clean the tape drive heads.  We have included a request in our installation
instructions for users to clean their drives BEFORE attempting installation.

In a few cases (0.01% of tapes produced) we find that even with a clean tape drive that there is an
actual tape error.  We are researching these to find what in our processes could be causing this.

A third possibility is that the tape drives were not calibrated correctly when manufactured.
Although we have not seen evidence of this, we are keeping our ears open.

Bob Green
Software QA Mgr
Silicon Graphics, Inc
(bobg@sgi)
(415) 962-3438