Scrub free disk blocks

Marko Vojinovic vvmarko at
Sun Aug 29 19:08:40 UTC 2010

On Sunday, August 29, 2010 09:16:28 Bruno Wolff III wrote:
> On Sun, Aug 29, 2010 at 07:46:49 +0100,
>   Marko Vojinovic <vvmarko at> 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.

Yes, but given a certain number of rewrites of each region, the old data is 
bound to be rewritten sooner or later, right? In addition, if this overwriting 
is a random process in terms of a precise spot where data is written, you 
cannot hope to be able to recover *all* (or a high percentage of) old 
information. I guess that after 2 or 3 rewrites of the whole disk, the large 
portion of the original data gets completely overwritten, and only random bits 
of that data can be recovered, in amount that is too small to be useful for  

I have an old Seagate 1.2 GB hard disk from 10 years ago, which is still 
operational on one of my machines at home. If we assume that over these 10 
years I have rewritten it 1000 times, the total amount of data that passed 
through the disk is cca 1 TB. I simply don't believe anyone is able to recover 
whole 1 TB of data from this disk, no matter how big budget and equipment one 
may have. I don't even believe they could recover even 20% of that terabyte.

So I still don't see how the original statement may hold. There just has to be 
a limit of how much information can be stored on a disk, and once you overflow 
this limit, old data is bound to get lost.

Best, :-)

More information about the users mailing list