Failed Recovery

How to recover from a previous failed attempt

Recently a camera memory chip was received where the customer has made a mistake worse by trying to recover with software that allowed the data to be written back to the memory chip.  The original problem was deleted files on a FAT camera memory chip.  About 60% of the original files remained, but about 40% were deleted.  The recovery program tried to undelete and then write the photos back to the original memory.  Although at times this works, in this case, the original files were fragmented, and so most if the apparently recovered files were corrupted.

The problem with this memory chip is that the files had been written with a new valid FAT and so the fragmentation errors had now been added to the files.  Fortunately, CnW recovery software has tools to recover fragmented files.

By performing a recovery of the files and then viewing the log, it was clear that many of the original files (ones not deleted) were fragmented, in some cases with 7 fragments.  Processsing fragmented files works best when it is possible for the program to eliminate areas of known good data.  Thus (having taken a safe guard image of the disk),  the recovered files were deleted.  As all the recovered file had a generic name, it was a simple operate to just delete them.  The memory chip was then close to the original state after the files had been deleted by mistake.

The next stage was with CnW, to use the Recover function, but to also add in the options of ‘Recover unused space’ and ‘Process fragments’.  The program will then read all valid files before examining the used unused area for remaining files (jpegs in this case). The fragments are then added together in a automatic, slightly trial and error process until valid photos are found.  By doing this, about 80% of the deleted files were recovered.  Of the unrecovered files, some were lost in the original recovery procedure.

Image Raw

A second possible approach would be to use the Image Raw function, with options to Split on file star, and process fragments.  This will work, but as it ignores known good files, the process is much slower, and more potential problems as every possible cluster has to be tested.  With processing fragments, there is always the possibility of false matches, though the CnW contrast option allows different runs to be made at different settings.

Speed

The processing speed to fragmented reconstruction is not fast, so be prepared to wait.  The screen will always indicate movement, so the process can be tracked.

How to avoid this problem

There are two ways to avoid this potential problem.  Firstly, always make an image copy of your data media, and secondly, NEVER write anything to this media.  The process above gets very close to the writing to the media when the recovered files were deleted.  If this stage was not done, then the only solution would be use the complete Image raw option described above.

 

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