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From: leres@ucbarpa.Berkeley.EDU (Craig Leres)
Newsgroups: comp.unix.questions
Subject: Re: QIC-11, QIC-24 and dump(8) tape length
Message-ID: <20040@ucbvax.BERKELEY.EDU>
Date: Sun, 9-Aug-87 20:35:33 EDT
Article-I.D.: ucbvax.20040
Posted: Sun Aug  9 20:35:33 1987
Date-Received: Mon, 10-Aug-87 00:10:52 EDT
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Reply-To: leres@ucbarpa.Berkeley.EDU (Craig Leres)
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This is a question I recently answered on comp.sys.sun.

The QIC-24 format makes 9 passes over the tape. The general formula
for figuring out how many feet of tape dump can use is:

	dump_tape_length = (actual_tape_length - 25) * no_of_passes

So when doing dumps, you should use something similar to one of the
following:

	dump 0uncbsf 126 2475 /dev/rst8 /mnt	# QIC-24, 300 foot tape
	dump 0uncbsf 126 3825 /dev/rst8 /mnt	# QIC-24, 450 foot tape
	dump 0uncbsf 126 5175 /dev/rst8 /mnt	# QIC-24, 600 foot tape

QIC-11 only makes 4 passes:

	dump 0uncbsf 126 1100 /dev/rst0 /mnt	# QIC-11, 300 foot tape
	dump 0uncbsf 126 1700 /dev/rst0 /mnt	# QIC-11, 450 foot tape
	dump 0uncbsf 126 2300 /dev/rst0 /mnt	# QIC-11, 600 foot tape

I think the recent consensus is that a block size of 126 is optimal.

		Craig