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From: rbraun@spdcc.COM (Rich Braun)
Newsgroups: comp.unix.sysv386
Subject: Tape trivia (was Re: SCO/mountain streamer)
Message-ID: <6806@spdcc.SPDCC.COM>
Date: 9 Mar 91 16:05:57 GMT
Organization: Kronos Inc., Waltham, Mass.
Lines: 38


This is a related question, regarding cpio under SCO and AIX:

	How do I read tapes across two machines with byte-swapped
	architectures?

If I create a tape (or disk archive) with cpio under SCO, and another
under AIX, then swap the two tapes, neither machine can read the other's
format.  If I "od" the tape dump, I see that the header bytes seem to
be swapped for each 16-bit short word.

The -s, -S, and -b byte-swapping options to cpio seem to have no effect on
either system; I still get "bad magic number" complaints.  I haven't tried
-c, to store file headers in ASCII mode rather than binary mode.  It just
ought to work; indeed it annoys me that any software/hardware developer
would create a machine architecture-dependent tape archive format.

How do I write tapes which are compatible between SCO and AIX (on the
RS-6000)?  Obviously, 'tar' will do the trick, but 'cpio' has more
error recovery logic.

Another question:  how do I write multiple cpio archives to a single
tape?  My AIX system doesn't seem to have the no-rewind device defined
(and I can't find this item in the documentation), and SCO Unix doesn't
seem to provide decent end-of-tape error handling.  You have to tell
cpio how large your tape is, in kilobytes, which won't work correctly if
you try to write multiple archives to one tape.  Also, because there
seems to be no way to "seek to the beginning of the current archive"--
it seems you have to rewind the tape and skip over the archives, an
exceptionally slow process--I'm beginning to believe that I ought to just
punt the idea of storing more than one archive per tape.

Finally, how does one write to low-density media on a high-density
Mountain drive under SCO Unix?  I have some old DC-300 tapes which I
can't seem to use at all.

Thanks for the help.
-rich