On 29 Aug 2010 at 3:16, Bruno Wolff III wrote:
Date sent: Sun, 29 Aug 2010 03:16:28 -0500
From: Bruno Wolff III <br...@wolff.to>
To: Marko Vojinovic <vvma...@gmail.com>
Subject: Re: Scrub free disk blocks
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> On Sun, Aug 29, 2010 at 07:46:49 +0100,
> Marko Vojinovic <vvma...@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.
Recalling a presentation at Defcon 2006, the space between tracks would
contain information that could determin what was there before a format
operation. A DES level wipe required writing 7 different patterns to every
sector to make this practically impossible.
I don't do that level of wiping disk, but do use scripts to clear the unused
space before doing disk/partition images. Makes a huge difference in the
image size, since zeroed out sectors compress to almost nothing in the
image file. Did an image of an 80GB disk after a full install of Fedora, and it
made a 12GB image file. After clearing the image was only 2.5GB.
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