Path: utzoo!attcan!uunet!cs.utexas.edu!longway!std-unix
From: henry@zoo.toronto.edu (Henry Spencer)
Newsgroups: comp.std.unix
Subject: Re: portability of tar tapes
Message-ID: <799@longway.TIC.COM>
Date: 7 Jul 90 23:39:29 GMT
References: <792@longway.TIC.COM>
Sender: std-unix@longway.TIC.COM
Reply-To: std-unix@uunet.uu.net
Lines: 36
Approved: jsq@longway.tic.com (Moderator, John S. Quarterman)

From:  henry@zoo.toronto.edu (Henry Spencer)

>From: cazier@mbunix.mitre.org (Cazier)
>How portable are tar tapes from one machine to another. My experience
>has been that tar within a vendor's site is portable but to try to
>carry a tar 1/4" tape from one vendor to another...

It is necessary to distinguish two issues here:  the tar format, and the
physical recording format.  The latter is whether you can get data off
the tape at all; the former is whether you can understand it.

Tar format is, if anything, significantly more portable than cpio, because
there has basically been only one version of tar format (plus some recent
upward-compatible extensions), whereas there have been several (different
and incompatible) versions of cpio.  The one problem that comes up now
and then is byte-swapping, due to broken hardware/drivers in certain
manufacturer's systems (I won't mention any names, except SGI :-)),
but a simple run through `dd conv=swab' solves that.

Physical recording format, especially on quarter-inch cartridges, is
another can of worms entirely.  There are too many different quarter-inch
recording formats to conveniently count, and new ones keep popping up.
If the recording format of the originating system is incompatible with
that of the reading system, it doesn't matter whether you're using tar,
cpio, ANSI standard magtape format, or whatever -- you *cannot* read
that tape.  Mercifully, there is basically only one format per density
on half-inch tape, and likewise on 8mm, and the appalling mess of floppy
formats settled down considerably when IBM's formats stomped all the
others (well, most of them, we won't mention Apple...) into oblivion.
Unfortunately, as I recall there are two formats on DAT, which isn't a
good start for a new technology.

                                         Henry Spencer at U of Toronto Zoology
                                          henry@zoo.toronto.edu   utzoo!henry

Volume-Number: Volume 20, Number 113