Help: mt erasing tapes?

[David Mazieres <dm_(_at_)_amsterdam_(_dot_)_lcs_(_dot_)_mit_(_dot_)_edu>]

My recent backup tapes all seem to be garbage.  I can take a level 0
backup, but when I try to reposition at the end of the tape for the
level 1, just running mt seems to trash the backup tape.

For example, after a set of level 0 dumps, everything looks fine
(though I didn't check the first file, a dump of /):


	# restore -i -f /dev/nrst0 -s2
	restore > what
	Dump   date: Wed Apr 10 11:23:32 1996
	Dumped from: the epoch
	Level 0 dump of /usr on ex-dis.lcs.mit.edu:/dev/sd0e
	Label: none
	restore > # 
	# restore -i -f /dev/nrst0 -s2
	restore > what
	Dump   date: Wed Apr 10 11:37:10 1996
	Dumped from: the epoch
	Level 0 dump of /var on ex-dis.lcs.mit.edu:/dev/sd0f
	Label: none
	restore > # 
	# restore -i -f /dev/nrst0 -s2
	restore > what
	Dump   date: Wed Apr 10 11:37:25 1996
	Dumped from: the epoch
	Level 0 dump of /usr/local on ex-dis.lcs.mit.edu:/dev/sd0g
	Label: none
	restore > # 
	# restore -i -f /dev/nrst0 -s2
	restore > what
	Dump   date: Wed Apr 10 11:52:01 1996
	Dumped from: the epoch
	Level 0 dump of /disk/ex0 on ex-dis.lcs.mit.edu:/dev/sd0h
	Label: none
	restore > # mt rew
	# restore -i -f /dev/nrst0 -s2
	restore > what
	Dump   date: Wed Apr 10 11:23:32 1996
	Dumped from: the epoch
	Level 0 dump of /usr on ex-dis.lcs.mit.edu:/dev/sd0e
	Label: none
	restore > # mt rew

Then I reposition to the end of the tape:

	# mt -f /dev/nrst0 rewind && mt -f /dev/nrst0 eom

At which point trying to read forward gives me an error:

	# restore -i -f /dev/nrst0 -s2
	tape read error: Undefined error: 0
	# restore -i -f /dev/nrst0 -s1
	tape read error: Undefined error: 0

Okay, that's what I would expect.  Now I rewind the tape and try to
read from the beginning again:

	# mt rew
	# restore -i -f /dev/nrst0 -s2
	tape read error: Undefined error: 0
	# restore -i -f /dev/nrst0 -s1
	tape read error: Undefined error: 0
	# restore -i -f /dev/nrst0 -s1
	tape read error: Undefined error: 0
	#

No dice.  I can't get data off the tape any more, even after ejecting
and re-inserting.

Any ideas?

Thanks,
David