From - Mon Sep 16 15:50:48 1996
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From: Irv Lustig <irv@dizzy.cplex.com>
Subject: Re: How to tell how much of a DAT tape is full?
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To: Peter Shenkin <shenkin@still3.chem.columbia.edu>
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Organization: CPLEX Optimization, Inc.
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Date: Wed, 11 Sep 1996 15:11:44 GMT
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Peter Shenkin wrote:
> 
> Given a DAT tape in the drive, with a single tar set on it, how can
> I figure out what fraction of its ~2Gb capacity is used up?
> 
Here's what I use.  I do nightly backups via /sbin/dump, so there are
tape markers between each dump.  I dump multiple file systems to
/dev/nrtape, so that each dump is separated by a tape marker.
After a dump of a single file system is complete, I use the following
csh excerpt:

mt status >& /tmp/mts.$$
set blk=`cat /tmp/mts.$$ | tail -1 | awk '{print $NF}'`
rm /tmp/mts.$$
@ left = $taplen - ( $blk / 100 ) - 1
/sbin/dump "$level"uCf $left"k" /dev/nrtape   filesystem

At this point, $left gives me the amount (in 1K units) of 1K blocks left
on the tape. For $taplen, I use 2000 for 90m tapes, and 1333 for 60m
tapes. Note that I am using the "C" option to dump to pass the remaining
capacity to the dump command.

This has worked pretty accurately for me so far.  I did some experiments
that seemed to indicate that the "mt status" command was returning a
block value that corresponded to approximately 10000 bytes per tape
block.

        -Irv Lustig                          irv@dizzy.cplex.com
        Director of Numerical Optimization   http://www.cplex.com/~irv/
        CPLEX Optimization, Inc.             http://www.cplex.com/