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From: rees@pisa.citi.umich.edu (Jim Rees)
Subject: Re: Tar
Message-ID: <50bc51ca.1bc5b@pisa.citi.umich.edu>
Sender: usenet@terminator.cc.umich.edu (usenet news)
Reply-To: rees@citi.umich.edu (Jim Rees)
Organization: University of Michigan IFS Project
References: <9104020018.AA18211@cml.unl.edu>
Date: Tue, 2 Apr 91 17:22:42 GMT

In article <9104020018.AA18211@cml.unl.edu>, gah@cml.unl.edu (Glen A. Hansen) writes:

  While on the subject of "tar", is it possible to "tar" more than one archive to
  a cartridge tape?

Not only is tar badly broken, but tape io is also broken (and always has
been).  You can make this work but it's a pain.  You have to rewind and
re-read each archive before writing the next.  The sequence is something
like this:

  mt -f /dev/rct8 rew
  tar cfv /dev/rct12 file1 file2 file3 ...

  mt -f /dev/rct8 rew
  dd if=/dev/rct12 of=/dev/null bs=1k
  tar cfv /dev/rct12 file4 file5 file6 ...

  mt -f /dev/rct8 rew
  dd if=/dev/rct12 of=/dev/null bs=1k
  dd if=/dev/rct12 of=/dev/null bs=1k
  tar cfv /dev/rct12 file7 file8 file9 ...

  ...

This takes forever.  In fact, it's intractable, since the time required is
exponential with the number of archives.  That means it doesn't matter how
fast the tape drive is, it still takes too long.