You are probably correct, given that current PRML encoding techniques 
and the given density of magnetic media (both drive and tape). The NIST 
specification even suggests that a single pass of random data would 
likely be sufficient (at least for drives, nothing is said of tapes). 
However it has been indicated to me that following the DoD/NIST specs is 
the minimum procedure, and they are the experts (not I ... although I 
like your test approach).

Given the apparent vagaries of tape data placement, job migration has 
been the only acceptable method (hence the tool was not necessary) 
albeit a rather lengthy procedure. Unfortunately given human nature, one 
I'm afraid will be repeated in the future (at least as long as we 
continue to use tape as and archive/backup method).
> It's surprising that such a "necessary" tool has never been written!
> Perhaps it's not as necessary as you think.
>
> Also, you're conflating drives and tapes, so I'll do the same.
>
> My experience with drive recovery companies suggests that it takes
> about 2kUSD to recover a drive.  And it's not always successful and it
> doesn't always recover all the data.  So the data better be worth at
> least that much.
>
> If your attacker is willing to spend $2k per tape to read your data,
> then maybe you can afford to destroy the $50 tapes and buy new ones.
> Or encrypt the data.
>
> IMHO, you should attempt to overwrite a tape with zeros then send it to
> the recovery company to recover.  This test will cost you ~$2k which is
> probably less than the development cost of this utility.  I'm willing
> to bet they won't be able to recover anything.
>
> Regards,
>    


Thanks for your thinking about this,
Paul Davis

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