Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!hoptoad!gnu
From: gnu@hoptoad.uucp (John Gilmore)
Newsgroups: comp.periphs
Subject: Reading past end-of-data on QIC-24 or QIC-11 cartridges
Message-ID: <7488@hoptoad.uucp>
Date: 31 May 89 21:46:28 GMT
Organization: Grasshopper Group in San Francisco
Lines: 31

A friend has a client who wants him to recover the data from a
QIC-24 cartridge tape that was damaged by doing a "tar c" rather
than a "tar x".  This overwrote the beginning of the tape, but
the rest of the data is still out there.  The problem is that
the tape drive, controller, or software drivers (not sure which)
will not let the tape go past the "blank tape" at the end of
the new empty tar file.

We reproduced the experiment on an Altos 386/2000 running Xenix 5.2,
and on a Sun-4 running SunOS 4.0.1 with a Sysgen/Wangtek SCSI tape drive.
We wrote a few megs of tar file on the tape, rewound it, and did
"tar cf $TAPE" to write a small empty tar file over the data.
Neither system would let us read past the first tar file; subsequent
dd's just give an error and transfer no data.  "mt fsf" spun the
tape but didn't have any other effect.  "mt status" reports "blank check".

My recollection from early Sun days was that the original Archive 
cartridge drives would let you go past the erased section (giving
errors for a while) and then read the old data.  Does anyone have
a system these days that can do that?  If so, whose software and
hardware are in it?

Such a capability is critical for error recovery in situations like my
friend's client's.  I'm not surprised that some bozo decided "users are
better off if we don't let them do this" but I am surprised that nobody
with expensive, inaccessible data sitting a few inches down the tape has
made them change it back.
-- 
John Gilmore    {sun,pacbell,uunet,pyramid,amdahl}!hoptoad!gnu    gnu@toad.com
  A well-regulated militia, being necessary to the security of a free State,
  the right of the people to keep and bear arms, shall not be infringed.