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From: wescott@Columbia.NCR.COM (Mike Wescott)
Newsgroups: comp.sys.ncr
Subject: Re: NCR Tape Formats
Keywords: Tape Quick-24 tar cpio formats compatibility
Message-ID: <1991Mar16.204126.1616@nncrcae.Columbia.NCR.COM>
Date: 17 Mar 91 01:41:26 GMT
References: <9906@exodus.Eng.Sun.COM>
Organization: NCR Corp
Lines: 36
Nntp-Posting-Host: micky

In article <9906@exodus.Eng.Sun.COM> petej@itcode.Eng.Sun.COM (Pete Jolly) writes:
> I always get:
> tar: directory checksum error (1 != 5663)

With tapes there are three areas of compatibility to check.  First is the
format (Q-24 et. al.), streaming tape drives on NCR Towers are capable writing
one format and  are capable of reading that format and (except for some old
models) of reading the next lower density format.  The inability to read is
ususally a consequence of the wrong format or of misaligned (or dirty) heads
on the writer or reader.  If dd(1) can read the tape, this is not the problem.

The second area (probably the case here) is byte-swapping.  Some multibus
machines using the 68k family of processors had this big-endian vs. little-
endian problem.  It usually only becomes an issue when interchange among
machines is required.  This can be overcome with

	dd if=/dev/rstp/... conv=swab  | ....

when necessary.  The newer Towers with SCSI tapes use the "right" byte order,
older machines use the swapped order.

The third area is the method of archiving. Use dd(1) to dump a few blocks from
the tape to a file.  Then use file(1) and od(1) to figure out whether tar(1) or
cpio(1) was used.  One can usually figure out the byte ordering this way as
well.  cpio archives have octal or ascii 070707 magic numbers at the start of
each file.  Byte-swapped it's 707070 for the ascii version and an octal 143561
for the non-ascii headers.  Tar archives begin with a file name.

Between byteswapping and tar vs. cpio I have been able to read tapes on Towers
made on a number of different machines.  Only the 3b2 seemed to go out of its
way to make life difficult for "foreign" machines.  Likewise, I would expect to
be able to read tar and cpio tapes made on a Tower, on other unix boxes using
the same techniques.
--
	-Mike Wescott
	 mike.wescott@ncrcae.Columbia.NCR.COM