recovery recommendations

[Stephen Samuel]

A simple one would be:
dd if=/dev/zero of=PARTIMAGE bs=1M count=184
(presuming that your original ISO was 185MB.  -- this leaves up to 1MB of
random crap, but (in my mind), that's better than tashing the good bits of
data.

You can get more accurate results by varying the block size and the count so
that they multiply out properly.
modern versions of DD recognize multipliers of K -> kilobytes, M->Megabytes,
G->gigabytes
  .. and those are the CS units (now called kibibytes, mebibytes,
gibibytes), not the marketing units.


On Sat, Jan 22, 2011 at 5:57 AM, Matija Nalis <mnalis-ml at voyager.hr> wrote:

> On Fri, Jan 21, 2011 at 10:51:20PM +0100, Florian Weber wrote:
> > * Keep a copy of your "unrecovered" disk image! You don't want to touch
> the
> >    original disk at all, so be prepared for making mistakes
>
> yes, that is always the most important step. And be extra extra carefull
> you
> don't nuke it by accident... readonly jumper on the drive (if it has one)
> helps.
>
> > * dd if=/dev/zero of=PARTIMAGE count=ISOSIZE
> >    where ISOSIZE is the ISO image's size in bytes
>
> actually, it is ISO image size in *blocks* [1], so this procedure would
> actually destroy 512 times more data than original error... :-|
>
> Anyway, let us know how it worked out...
>
> And if this procedure fails you, I'd also second the great experiences with
> http://www.cgsecurity.org/wiki/PhotoRec - works even if filesystem and
> partition structures are completely foobared...  If you use it and it works
> for you, don't forget to donate to the guy, there's link on the pages.
>
> [1] by default block size is 512 bytes, can be changed with bs= parametar
> to
>    dd(1) -- note that while you can use 1 byte as an unit, it will be
> terribly
>    slow; so it is probably best to use let's say bs=4K, divide ISOSIZE in
> bytes
>    by 4096, round it down to nearest integer, and use that as count=
> parameter.
>
> --
> Opinions above are GNU-copylefted.
>
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-- 
Stephen Samuel http://www.bcgreen.com  Software, like love,
778-861-7641                              grows when you give it away
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