Re: using dd to wipe a disk
- From: Jonathan Buzzard <jonathan@xxxxxxxxxxxxx>
- Date: Wed, 24 May 2006 23:06:33 +0100
On Tue, 23 May 2006 19:44:40 +0000, Dave {Reply Address in.Sig} wrote:
Tim Woodall wrote:
On Sun, 21 May 2006 20:35:46 +0000,
Dave {Reply Address in.Sig} <"noone$$"@llondel.org> wrote:
<snip> Certainly a
single pass wipe can be recovered with appropriate tools.
You see and hear this a lot but has anybody got a pointer to a paper or
a firm who have done this in practice for a modern hard drive?
I dno't know of any papers on the subject but the principle is that a
'1' bit remagnetised to a '0' is less strong than a '1' bit re-written
as a '1'. You've also got mechanical toleraces, although that's more
true of older drives with less bits per inch - if the heads are on a
slightly different track to last time then they'll leave slight traces.
To extract the information you'd need to remove the platters from the
drive and spin them up in a special rig with special heads, and probably
do a lot of statistics on the results. Definitely not cheap, given that
you'd have to recalibrate for each new set of platters.
They dismantle the drive and use a scanning GMR head to build up a
picture of what is on the drive (so a bent platter is still readable).
It is *very* expensive, the figures I have seen start at £20k with no
guarantees of recovering a thing.
JAB.
--
Jonathan A. Buzzard Email: jonathan (at) buzzard.me.uk
Northumberland, United Kingdom. Tel: +44 1661-832195
.
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