Scrub free disk blocks

[Bruno Wolff III]

On Sun, Aug 29, 2010 at 07:46:49 +0100,
  Marko Vojinovic <vvmarko at gmail.com> wrote:
> 
> Starting from the premise that every hard disk has in principle limited 
> capacity to store data, one can always fill it up completely, then rewrite it 
> completely again. I see no way of the old data being recoverable, because this 
> is in contradiction with the fact that the disk was filled up completely two 
> times. The old data has to be destroyed in order to make room for new data. At 
> least as far as I can understand it.

At least at one time it was possible because the data is stored in a region
and when overwriting the region you don't hit the same spot every time.
With the right equipment you could see these areas and tell what data had
been written in that spot in the past.

I have heard that with the current generation of disks this is no longer
practical. But practical is mostly defined by what your budget is; so if the
data is valuable enough, it is potentially recoverable.