Recover failed SD card

Polytropon freebsd at
Sun Feb 24 07:10:54 UTC 2019

On Sun, 24 Feb 2019 07:53:28 +0100, Andrea Venturoli wrote:
> On 2/24/19 5:53 AM, Polytropon wrote:
> > Did you ask your customer to recover from his backups?
> > Yes, of course you did. :-)
> "Back-what"? :)

"We don't need backups - we have RAID!" ;-)

> > This will probably apply to _any_ copying tool. For things
> > where dd fails, I often try dd_rescue and ddrescue
> As I said I tried "recoverdisk" (which is like ddrescue, but it's in base).

It suffers from the same problem as probably all tools will:
System reports "end of medium", and that's it. :-(

> >> The card should hold pictures, so I could go ahead with photorec once I
> >> got an even partial image.
> > 
> > That is the recommended approach. Maybe you can already recover
> > a fraction of the images stored on the card.
> Tried that before posting; it finds nothing.
> To me it looks like I'm not even seeing the *first* 120 MB of the card.

That's quite possible. I assume the card is supposed to carry
a FAT file system. For technical purposes, that file system
doesn't have to begin at the _start_ of the memory unit. The
controller might use several MB for internal use, such as
"re-mapping" and "accounting", and the actual "payload" begins
later - in an area that the controller does no longer present
to the media interface.

It sometimes helps to use a file viewer to check what's in
the obtained image, or a hex dump. If you get only 0x00 bytes,
it's even "worse than garbage", because garbage could mean
something (like "mutilated former file content").

> > There is another possibility, but it's actually _very_ hard
> > to do, and it's not guaranteed to work:
> > 
> > Obtain an identical SD card. It has to be "as identical as
> > possible": same control unit, same memory unit, same firmware
> > revision (yes, there's "a whole computer with hard- and software"
> > on that thing!). Transplant the old memory chip to the new
> > card, removing its new memory chip (empty) beforehand. Then
> > try another identification.
> > 
> > If it's a micro-SD card, don't inhale the chip. ;-)
> It's a micro-SD card and I'm not able to do this.

As I auggested, this approach takes a _lot_ of work (and very
specific tools & skills), and you might end up with the same
result you're seeing now...

Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...

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