What's in my hard drive? How can I get rid of it?

[Roland Smith]

On Tue, Feb 17, 2015 at 06:37:38PM -0600, Valeri Galtsev wrote:
> 
> On Tue, February 17, 2015 5:30 pm, Daniel Feenberg wrote:
> >
> >
> > On Tue, 17 Feb 2015, Michael Powell wrote:
> >
> >> jd1008 wrote:
> >>
> >> [snip]
> >>
> >> Remove the cover. Remove the platters. Smash all platters with large
> >> sledge
> >> hammer until all pieces are fairly small. Melt material with
> >> oxyacetylene
> >> welders torch. Repeat smashing with hammer. Soak for few hours in
> >> hydrofluoric acid. Rinse and allow to dry. Grind material into a fine
> >> particulate dust. Dispose of out the back of airplane while flying or
> >> drop
> >> into convenient nearby volcano. That might be good enough.
> >>
> >> Send the electronic components to Kaspersky for analysis.
> >
> > I did once investigate claims that overwritten sectors could be read by
> > sophisticated instruments and posted my results at:
> >
> >    http://www.nber.org/sys-admin/overwritten-data-gutmann.html
> >
> > In short - that is pure science fiction.
> >
> 
> Interesting. I never saw this particular explanation. I have heard that
> overwiritten data can be recovered (to significant extent).

From “Overwriting Hard Drive Data: The Great Wiping Controversy” by Craig Wright,
Dave Kleiman, and Shyaam Sundhar R.S;

To start with;

    The acquisition time for 1 byte is about 4 minutes.

At that speed, you can read 128 KiB in a year! Furthermore:

    Consequently, we can categorically state that there is a minimal (less
    than a 0.01% chance) of recovering any data on a NEW and unused drive that
    has a single raw wipe pass (not even a low-level format). In the cases
    where a drive has been used (even being formatted for use) it is not
    possible to recover the information – there is a small chance of bit
    recovery, but the odds of obtaining a whole word are small.

Conclusion:

    Although there is a good chance of recovery for any individual bit from a
    drive, the chances of recovery of any amount of data from a drive using an
    electron microscope are negligible.

You can get the paper from e.g.
http://www.vidarholen.net/~vidar/overwriting_hard_drive_data.pdf

A single wipe of a HDD is enough to destroy the data beyond hope of recovery.

For an SSD or other flash-based storage the picture is different. For one
thing, because of the controller on those storage devices you cannot be sure
that overwriting a block of data on location X actually is written to location
X.


Roland
-- 
R.F.Smith                                   http://rsmith.home.xs4all.nl/
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