Datarecovery from overwritten tapes was Re: Reading DC100a tapes

Nico de Jong wrote: The error recovery on serpentine recorded tapes uses a tape block number to do data recovery. The QIC tapes did not backspace to do error recovery in general. If a read after write occurred, it would throw out more blocks of the error data, and at read time the order would have to be sorted out by the read firmware. For whatever brilliant reason, the QIC designers and implementors never designed in any useful error recovery and published it. So as a result, the fact that the QIC tape firmware throws it's hands up and dies leaves you with your problem. I would think that if you can read the track in binary, and pick out the block numbers and decode them, you should be able to do the recovery. The key is finding a drive that will read the track, and having total access to it. Sounds like Al is up to that, so you might be able to pull this off. Several "data recovery" guys I dealt with back in the day were ex Tandberg tech guys who had gotten hold of secret or confidential (to hear them tell it) diagnostic software, and some of the tape drives and they would be able to read over defective parts of the recorded tape. I dont know of any other QIC drive that had such utilities available. I believe that they used the 1gb or 2gb model tandberg's which were 5 1/4" form factor to do this. If anyone has or knows of such, maybe they can comment on whether these programs are now available. The time frame I am talking about is to 90 or so. Jim