Try re-labelling the volume and running the AUDIT VOLUME command on the bad
tape volume first.  If that doesn't work, you must resort to the procedure
that David Boyes outlined.  David's procedure should work, but I think he left
out one step.  When creating a copy of the bad tape, you should "pad" the copy
with "blank" tape blocks.  If you just copy the good data from the original
tape starting just past the VOL1/HDR1/HDR2/TM on the copy, all the data will
be in a different place (relative to the beginning of the tape).

To find out the number of blocks you need for padding, use your favorite tape
browser (e.g. DITTO) to locate the first valid ADSM tape block (just past the
overwrite).  Note that with 3490E drives, you will probably have to skip way
past the overwritten part, then backspace blocks.  Encoded in each tape block
is an eyecatcher in bytes 0-3 ("TQBH"), and the position (block id) as returned
from the control unit in bytes 4-7 (the second fullword).  Ignore the first
byte and a half of the position, and the rest of it contains the block number
in hex.  Using that number, subtract 4 to account for the labels and the tape
mark, and that's the number of blocks you need for padding.  The blocksize is
32760.

After you write the padding blocks, copy the original tape to the end, then
do the AUDIT VOLUME FIX=YES.  If this doesn't work, you're left with deleting
the volume and discarding all the data on the volume.

Wayne Hineman
IBM Almaden Research Center