Re: [gentoo-user] The sudden disappearance of ....WHAT??? (I/O error on a SD flash card?!)

[Fabio Scaccabarozzi]

Hi tuxic,

That looks like an output from photorec. Generally photorec only reads the
whole disk block by block, when it finds information in the filesystem's
metadata - either inode table or inodes themselves - you're lucky and you
get filenames, otherwise you only get that kind of output. Consider that
all those items might as well be deleted items, so you might be getting
back a lot of cruft.
I never had to use the functionality so I cannot comment on how good it
works, but testdisk allows you to restore partitions by scanning the entire
disk/image searching for superblocks and partition metadata. That might
give you a chance of restoring the superblock of the partition and
salvaging at least some part of the data. See a guide on testdisk's
official website -> http://www.cgsecurity.org/wiki/TestDisk_Step_By_Step
Consider that by default ext4 partitions should have superblock backups
spread out at fixed intervals during the filesystem creation, so this
should work better than trying to blindly carve the data out of the
partition.
Before applying fixes to the image file make a backup in case something
gets screwed up :-) Testdisk might detect additional stuff that looks like
partition info, but it's not.

Il giorno dom 26 mar 2017 alle ore 11:37 <tuxic@××××××.de> ha scritto:

> On 03/26 08:10, Adam Carter wrote:
> > > Currently I am ddresucueing the flashcard to the harddisc.
> > >>> Next I will try to mount the sdcard.
> > >>>
> > >>>
> > I hope you meant to say "mount the sdcard image". Once ddrescue has done
> > its best, you wont try to use the sdcard again.
> >
> > Also, you probably want to copy the image first, because when you try to
> > fix it you will perform writes, and you dont want to lock yourself out of
> > other recovery options by making potentially damaging writes.
> >
> >
> > > What reliable sdcard-reader can one recommend ?
> > >>>
> > >>
> > I'm not sure what you mean here given that you're making an image with
> > ddrescue.
> >
> > Is the assumption correct, that -- if ddrescue could read each
> > >> partitions of the sdcard without stuttering, retries and errors --
> > >>
> > > the sdcard itsself is ok and "only" the logical structure
> > >> (fs, superblock etc) got damaged?
> > >> Or do I overlook something?
> > >>
> > >
> > If ddrescue can read it cleanly with no retries (in which case it will
> > offer no benefit over dd) then yes, I agree. However, given the cost of a
> > card and the cost of your time and the risk to your data, I wouldnt be
> > using it.
> >
> >
> > > I dont know of a cdparanoia type recovery utility for sdcards but I
> > > suspect sdcard design means that approach wont work.
> > >
> >
> > I would just use photorec against a copy of the image. I have done this
> in
> > the past and recovered many files from a ddrescued image of a failing USB
> > drive, however, all the filenames were lost.
>
> Hi,
>
> I copied the image of course and umounted the sdcard as soon as
> possible.
>
> As in my previous posting, as long the recovered files are images,
> the lost of filenames my be annoying...
> But in case of files of a Android system (from which the sdcard
> originates) the lost of filenames is equivaltent to the lost of
> the file itsself...
>
> Cheers
> Meino
>
>
>
>
>