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Re: How do I know I,m getting 60 G. Compressed on 3590E's?

2000-05-09 14:12:50
Subject: Re: How do I know I,m getting 60 G. Compressed on 3590E's?
From: Rob Schroeder <robs AT FAMOUSFOOTWEAR DOT COM>
Date: Tue, 9 May 2000 13:12:50 -0500
Actually you can't.  I have even talked with IBM on this issue.  Even if you
could find the number of bytes on the tape it would still not tell you.  Here is
why....  Up to 51% of a 3590 tape can be used by overhead of the tape drive.
Since the 3590 uses "RAID-like" technology to write to the tape, that overhead
information is physically stored on the tape.  That overhead information can
take up to 51% of the total capacity of the tape and cannot be determined
without analyzing every byte on the tape.  The ability to do this is not
distributed to users, and even most of IBM.  Also, the estimates of 20G to 60G
are quite inaccurate.  IBM gives those as averages and not concrete ratings.  On
our 3590 tapes we get anywhere from 4 Gig to 80 Gig per tape, it depends on the
types and sizes of files being saved.

To make my long story a bit longer, there is no way to determine how much
information is stored on a single tape.   Even if you could determine one tape,
it would not accurately compare with another tape's size.

Rob Schroeder
Famous Footwear
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