[sf-lug] recovery after dd

Dennis J Harrison Jr dennisharrison at gmail.com
Mon Sep 6 11:38:40 PDT 2010

On Mon, Sep 6, 2010 at 12:18 PM, Sameer Verma <sverma at sfsu.edu> wrote:
> On Sun, Sep 5, 2010 at 7:40 PM, Brian Morris <cymraegish at gmail.com> wrote:
>> On 9/5/10, Sameer Verma <sverma at sfsu.edu> wrote:
>>> I have an old external USB drive (120GB, I think) that had a bunch of
>>> files and was close to full. I ran dd on it and installed a 2.1GB
>>> image.
>> I don't know about anyone else, but it is unclear to me
>> a) exactly what the original condition of the drive was
>> b) exactly what you did (arguments to dd ? what did you do by
>> "installed" you say ?)
>> c) where did you get the idea of doing this ? didn't they say how to
>> the other half of the method ?
>> Without this information, it would be hard for anyone to give any
>> guidance as to what to do as far as I know.
>> Brian
> Sending this out to Brian and the list. He forgot to cc list.
> Hi Brian,
> This is an experiment. I had a external USB drive lying around (close
> to full), so I'm playing with it. I also had a 2.1GB image from an
> earlier experiment, so I used dd if=image.img of=/dev/sdc1 bs=1M but
> what I want to figure out is if the data past 2.1GB is recoverable.
> Hope this clarifies.
> cheers,
> Sameer

For what it's worth - this sounds like a blast.  Perfect thing to
spend a beer session with on this holiday.  I'm filling up a 16gb
drive right now to try this out.  My guess is that the remaining data
will be recoverable.  I've very little knowledge of the fundamental
workings of the rom, ram, nand and it's read / wrtie processes.  If
the data isn't recoverable - I'll be reminded of just how little I
know :)

All the 1s and 0s on the other side of the partition should still be
the same.  Unless for some reason the mass storage controller itself
does something special when a partition is created (doubt) ?

Essentially/Electronically speaking, electrons pass through two or
more gates - one of them being a control gate.  The control gate
passes electrons to a floating gate which then pushes the electrons
through some oxide(ish?) layer.  The negative electrons then act as
resistance.  There is a sensor which measures this to determine if it
should report 0 or 1.  This happens per block (as far as I know, newer
tech might do some neat stuff here and there).

So, another few minutes on this transfer, then I've got to find a
smaller drive I can dd to it.

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