Misaligned tape heads. SERIOUS data-loss possibility.

[Omar A. Karim]

Misaligned heads can cause tape I/O to be 'unique' to a particular tape
drive.  I discovered this due to the following chain of events:

(1) Machine crashed, trashing root partition.
(2) Attempts to boot of tape FAILED due to I/O error
(3) SUN came down and found tape drive was faulty, replaced drive.
(4) I attempted to restore the root partition from a level 0 dump...
(5) ... and the NEW tape drive wouldnt read the tape!!
(6) Fix: we booted off the tape using the NEW drive, switched drives after
    boot. Now the OLD tape drive could read the dump tape. Restored.

I am wondering if anyone has a fix to this rather dangerous scenario:
1) Tape head gets misaligned. No symptoms, backups continue as usual, errorfree.
2) Tape drive crashes IRRETRIEVABLY, system crashes......
3) Replacement drive cannot read your DUMP tapes. 

Is all lost? Is there a way to check the head alignment? I can think of
periodically reading the OS distribution tapes as a 'check'.

BOTTOM LINE:  Misaligned tape heads can make ALL your dumps USELESS!

Worriedly yours
Omar A. Karim
karim at ecsvax.uncecs.edu