shredding files on a flash drive

[James Knott]

Kristian Erik Hermansen wrote:
> On Jan 25, 2008 11:00 AM, James Knott <james.knott-bJEeYj9oJeDQT0dZR+AlfA at public.gmane.org> wrote:
>> Can you be so certain?  Many years ago, I used to maintain mini-computer
>> systems, including disk drives.  There were many times I would repair a
>> drive after a head crash and then do an alignment of the heads etc.
>> When you do that, one thing that's obvious is that the data is recorded
>> in clearly identifiable tracks, which you can locate by watching the
>> recovered signal with an oscilloscope.  What's to stop someone from
>> reassembling those platters in a similar drive and, with perhaps some
>> effort, recovering that data?  It may be difficult, but I not
>> impossible.  I know it's possible to align a drive to the data on a
>> disk, because I've done it.  You might also want to talk to someone in
>> the data recovery business.  IIRC, there was a presentation by one such
>> person at a TLUG meeting a few years back.
> 
> I have spoken to people in the data forensics field, yes.  With
> multi-platter disk drives, I encourage anyone to prove me (and the
> forensics guys) wrong.  The problem is that newer disks are aligned
> and sealed at the same time in the factory.  The tracking information
> is written to the disk while it is enclosed.  I don't see how you
> would determine how to align the tracks from data which you cannot
> determine is valid data or not.  Please explain and show proof.  Btw,
> I have done and consulted with forensics experts about the situation
> you speak of -- using a similar drive to recover data.  I encourage
> anyone to provide evidence that it is possible.  There is no evidence,
> that I have seen, to support it.  However, there is a multitude of
> evidence to show that once you misalign the platters, your data is
> toast...

First, read up on how data is recorded on the platters.  It is in 
concentric tracks.  By moving the head gradually across the surface of 
the disk, you will see where the data lies.  The tracks themselves 
provided the alignment information, that the drive uses to maintain the 
head position.  The tracks also contain the clock, used for data 
recovery.  Please note, I am not saying that you could simply drop the 
platter into another drive and read them as though they were in the 
original drive.  It may take a significant amount of effort.  But as 
long as you can move a head across the surface and read the signal, the 
data can recovered.  But then again, what do I know?  I'm only a former 
computer tech, who used to do disk repairs as part of my job.  Perhaps 
you should ask some of those people how many drives they've repaired.

BTW, some of the drives I used to work on had as many as 20 surfaces.



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