Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!mp.cs.niu.edu!ux1.cso.uiuc.edu!shair
From: shair@ux1.cso.uiuc.edu (Bob Shair)
Newsgroups: comp.unix.aix
Subject: Re: Tape terror
Message-ID: <1991May20.162055.29140@ux1.cso.uiuc.edu>
Date: 20 May 91 16:20:55 GMT
References: <7552@spdcc.SPDCC.COM> <3931@d75.UUCP> <7572@spdcc.SPDCC.COM>
Distribution: usa
Organization: University of Illinois at Urbana
Lines: 43

rbraun@spdcc.COM (Rich Braun) writes:

>A question for IBM:  why _in the world_ would a company put out a product
>which by default would do such a thing?  It really makes the system seem
>cruddy and slow.  To the uninitiated (myself, for example), it may not
>be all that obvious that one should go into the SMIT menu and change a
>simple, relatively unexplained parameter.  After all, it's very easy to
>screw the system up by changing parameters one does not understand; my
>inclination is to leave things well enough alone if they aren't broken.

>This truly amazes me.

>-rich

Rich, I usually refuse to answer "why" questions, and I'd like
to emphasize that this is my personal guess.  I don't know anything
about this (some people won't be surprised).

Automatically retensioning maximizes the chance of long-term  
error-free operation.  In Info-Explorer, "retension the tape"
is listed as a PERIODIC "systems management task" for the QIC
tape drive.  Under the tctl command, it says that retension
"Moves the tape to the beginning, the end, and back to the
beginning of the tape.  If you have excessive read errors during
a restore operation, you should run the retension subcommand. 
If the tape has been exposed to environmental extremes, you should
run the retension command before the save operation."

In short, retension should be done when there's something wrong
with the tape, and also every now and then (for luck?).  

Not trusting the user to do this, we appear to have opted for
reliability over performance.  This is very IBM-like.
I tell my customers to 
 1) turn off automatic retensioning, and
 2) remember to retension the tape every now and then.


-- 

Bob Shair                          shair@chgvmic1.iinus1.ibm.com
Scientific Computing Specialist    SHAIR@UIUCVMD (bitnet)
IBM Champaign