Re: unable to repartition SD card from Android phone

[David Christensen <dpchrist@holgerdanske.com>]

On 05/27/2017 11:30 AM, Mark Copper wrote:
> > Does you SD card and/or SD card adapter have a write-protect tab or other
> > such mechanism?  If so, put it in the unlocked position.
>
> The micro SD cards used in phones don't appear to have such
> mechanisms, but your point is well taken; viz. I've not adequately
> checked the hardware path (MB, card reader, etc. red-faced here...)

I bought a SanDisk 32GB Micro SDHC card for my Android phone a while 
back.  It came with a Micro SDHC to SD adapter, and the adapter has an 
unmarked switch in the same style and location of the write-protect 
switches on my other SD cards.  I'm not sure if the switch actually does 
anything.


> > Have you tried using dd to wipe the first megabyte (including the partition
> > table)?
> >
> > # dd if=/dev/zero of=/dev/sdc count=2048; sync
>
> Yes, but no effect. Even count=1 gets to non-zero bytes:
>
> dd if=/dev/sdc count=1 | od -b
> 0000000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
> *
> 0000700 002 000 356 377 377 377 001 000 000 000 377 043 267 003 000 000
> 0000720 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
> *
> 0000760 000 000 000 000 000 000 000 000 000 000 000 000 000 000 125 252
> 1+0 records in
> 1+0 records out
> 0001000
> 512 bytes (512 B) copied, 0.00365101 s, 140 kB/s
>
> dd if=/dev/zero of=/dev/sdc count=1; sync
> 1+0 records in
> 1+0 records out
> 512 bytes (512 B) copied, 0.0170507 s, 30.0 kB/s
>
>  dd if=/dev/sdc count=1 | od -b
> 0000000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
> *
> 0000700 002 000 356 377 377 377 001 000 000 000 377 043 267 003 000 000
> 0000720 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
> *
> 0000760 000 000 000 000 000 000 000 000 000 000 000 000 000 000 125 252
> , 0.00290682 s, 176 kB/s
> 1+0 records in
> 1+0 records out
> 512 bytes (512 B) copied
> 0001000
>
> Maybe I'm not looking at this right...

I think you are looking at it correctly.  Your console session indicates 
that the drive appears to accept writes, but is actually discarding them.


> The idea that a card could be locked up by the OS is titillating but
> improbable. There would have to be an (apparently) unpublished trap
> door or a back door to the disk controller in a generic disk.  So it's
> gotta be hardware and this has all been noise.

Perhaps the drive firmware has decided the device is failing, and has 
forced read-only mode so that you have a chance to recovery any viable 
data (?).


Have you tried contacting technical support for the drive manufacturer?


David