About Flash Recovery and Flash Doctor
The challenges of flash data recovery without rebuilding the controller (through “Jigsaw Method”):
Like hard disk drive, flash devices also require bad block management by the device driver software, or by a separate controller chip. SD cards, for example, include controller circuitry to perform bad block management and wear leveling. When a logical block is accessed by high-level software, it is mapped to a physical block by the device driver or controller. A number of blocks on the flash chip may be set aside for storing mapping tables to deal with bad blocks, or the system may simply check each block at power-up to create a bad block map in RAM; but unlike hard disk drive, in flash-based storage devices, files are not stored linearly but in a dynamic unknown order decided by the “wear-leveling” algorithm running in the controller chip. The “wear-leveling” algorithm was invented to extend the service life of the devices. We know flash memory has a very limited read-write cycles because flash uses transistors as data storage devices, and the transistors within flash memory use electrical current to change their state (from a '1' value to a '0' value and vice-versa); if it uses the same data storage method as hard disk drive does, we can imagine that the front part transistors of the flash memory will be used very frequently and get damaged very quickly, while the latter part will seldom be used. The “wear-leveling” algorithm was introduced to solve such kind of problem: “wear leveling” will change the write position each time, for example, if one block has been used in a last write operation, the “wear-leveling” will use a new block for the next write operation, so that to make sure each of the blocks to be used equally, and to ensure a maximal service life of the device. The “wear-leveling” algorithm plays a key role in extending the life of flash devices, but as for flash data recovery, it becomes an annoying barrier: the data is totally out-of-order, and they are meaningless. Flash Doctor gets rid of this barrier by using the “Jigsaw Method” mentioned above; but since the “wear-leveling” algorithm is very complicated, most of the time we can’t get 100% data back. The success rate will be affected greatly by the complicacy of the data organization, for example, if there is regular ID code, and what is the state of the key parameters like channel swap, block swap, page swap and so on.
Flash data recovery using “Jigsaw Method” asks for a deep-enough knowledge background, users are required to have a deep understanding on the storage structure of flash memory; based on the result of our beta test, which includes 100 cases of data recovery from USB pendrive, SD cards, CF card and so on, the succeed rate of Flash Doctor is around 70% (please note this success rate was achieved by our R&D engineers, users might not be able to receive such a success rate in the beginning).
Conclusion: According to the descriptions above, I believe you have had a clear image of flash data recovery and Flash Doctor; flash data recovery is much more complicated the hard disk drive data recovery, and it has a strict requirement for the operators (have a deep understanding on the storage structure of flash memory), and its success rate can hardly reach 100%. Despite of the difficulty, data recovery by “Jigsaw Method” in flash memory is the way it should be, and it is for sure that along with the constant improvement and upgrade of the algorithm and the users gets more proficient with the tool, the success rate can be increased rapidly and continuously.
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