Question on shredding a terebyte drive

[Bruno Wolff III]

On Wed, Sep 02, 2009 at 16:37:26 -0700,
  "Dean S. Messing" <deanm at sharplabs.com> wrote:
> Thanks to all for the replies.
> 
> I'll answer most of the comments here.
> 
> 0) The disk is unmounted.
> 
> 1) The drive is (was) a backup drive with a great deal of sensitive
>    corporate laboratory research data and algorithms on it.  The
>    monitary loss of the data being stolen would be significant though
>    it's hard to put a $$ value on it.  More importantly, I'm following
>    corporate policy.
> 
> 2) The drive is under extended warranty and so I'm sending it back for
>    a new drive.  The Power Supply in the enclosure is bad.  The actual
>    drive is still good, but they want the whole thing back for a
>    replacement.  Sanding off the oxide and then melting the drive
>    probably won't go over well with the manufacturer.

Given 1, this seems like a foolish policy. Just eat the cost as part of
securing your data. It might be cheaper than having you keep an eye of
multiple write passes covering several days.

> 3) Writing zeros is a not a good idea if the data is valuable.  The
>    small latent magnetic orientation info left from the previously
>    written data is not _that_ hard to recover with $5000 equipment, so
>    I've read.  Multiple passes of random patterns are needed to make
>    recovery costly.

There was some old documentation that claimed reading the remmants from
previous writes were recoverable, though I don't remember seeing costs
estimates that low. I would have expected a lot of human time needed to
help deal with the incomplete recovery.

If one can recover a significant amount of data after writing zeros, one
is going to be able to do it after writing a single pass of random data
as well.