[GRLUG] Disk scrubber

[Michael Mol]

On 7/25/06, Benjamin Flanders <flanderb at gmail.com> wrote:
> On 7/25/06, Michael Mol <mikemol at gmail.com> wrote:
> > On 7/25/06, Tim Schmidt <timschmidt at gmail.com> wrote:
> > > On 7/24/06, Michael Mol <mikemol at gmail.com> wrote:
> > > > I read somewhere that shred's "doing more" is targeted at older-style
> > > > hard drives, like FM, MFM and others, and most of its routines aren't
> > > > any more effective on a modern disk than a simple overwrite.
> > > >
> > > > In essence, most of shred's passes were each designed for a different
> > > > style drive.
> > > >
> > > > Source:
> > > > http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html
> > >
> > > Possible.  However, I have used some professional data recovery
> > > software and witnessed data recovered from a 0'd drive (0'd by WD
> > > Diagnostics Disk).  Extra steps are welcome in my opinion.
> > >
> > > --tim
> >
> > Did that work by reading 0'd sectors, or by reading reallocated
> > sectors?  Just curious.
> >
>
> I always thought they could read the latent magnetic charge left over
> from the previous bit.

Depends on the device.  The ability for a read/write head to read
faint and overwritten signals is limited by the drive's circuitry and
the drive's firmware.

I know it's possible to access reallocated sectors on some drives,
with the right instructions sent to the drive.  However, accessing
overwritten data using the original read/write head and the drive's
built-in circuitry would require a firmware upgrade, if it's possible
at all.  The software Tim saw likely had access to the correct ioctls
to read reallocated sectors.  It's less likely, but still possible,
that it had the ability of changing the drive's firmware.

I asked because I was curious as to the nature of the software.
-- 
:wq