igb@fulcrum.bt.co.uk (Ian G Batten) (03/18/91)
I have a friend (really!) who has done a very careless thing. He inserted a QIC-11 tape which had some vital data on it which was write enabled into a tape drive and wrote a few kilobytes over the beginning of it. Given that I have kernel and driver sources for V.3 machines and various other equipment scattered about, can anyone suggest anything which might drag some of the data off? I've tried the obvious method of reading the tape to the end of media and then trying again using a non-rewinding open, but I simply get read failures. I assume the problem is that I have a partial block following the double tape mark. ian
martin@adpplz.UUCP (Martin Golding) (03/22/91)
In <1KL&MK$@uzi-9mm.fulcrum.bt.co.uk> igb@fulcrum.bt.co.uk (Ian G Batten) writes: >I have a friend (really!) who has done a very careless thing. He >inserted a QIC-11 tape which had some vital data on it which was write >enabled into a tape drive and wrote a few kilobytes over the beginning >of it. Given that I have kernel and driver sources for V.3 machines and >various other equipment scattered about, can anyone suggest anything >which might drag some of the data off? I've tried the obvious method of >reading the tape to the end of media and then trying again using a >non-rewinding open, but I simply get read failures. I assume the >problem is that I have a partial block following the double tape mark. It's worse than that. Each block is numbered, the formatter (the part of the drive that diddles the data) puts a header on each block with all kinds of interesting stuff. The same hardware knows better than to let you start reading in the middle of the tape, or read past the eom marker block. Without direct access to the electronics, you're not likely to get anywhere. In addition, most of the serpentine drives use erase bars; so you may have a data gap at the beginning or end of each track. On the other hand, it may be worth your time to contact the manufacturers directly. They'll know exactly how the firmware works, and might be able to tell you how to cheat it. ( I wrote the firmware for an obscure cassette drive, and I _think_ I could trick the drive into reading past the eom). OB scolding: Don't your friend's tapes have write protect :-/ ? Martin Golding | sync, sync, sync, sank ... sunk: Dod #0236 | He who steals my code steals trash. Blechtrottel CPU with many megs... {mcspdx,pdxgate}!adpplz!martin or martin@adpplz.uucp