Recovering flash-based storage
By memory card recovery we mean recovery from the various storage devices built on non-volatile NAND memory. These components contain no moving parts, unlike a hard disk, which is why they are also called solid-state media. The data on such cards is held on flash chips, and recovering it follows a very different path from recovering a mechanical drive.
A digital camera reporting a 'Memory Card Error' is usually the first sign that a card has been damaged.
Logical problems
Where the fault is logical, recovery is generally handled with software — some of it purpose-built — in order to work past the damage and reach a point where the data can be extracted intact. Accidental deletion, an interrupted write and a corrupted file system all fall into this category, and all of them have good prospects provided the card has not been used since.
Physical problems
Recovery from physically damaged flash media is considerably more involved and takes longer. It runs through several stages:
- Dismantling the card, which also reveals the type of memory and the controller in use
- Removing the memory component using SMD equipment — this has to be done carefully, since uncontrolled heating can burn the chip and cause irreversible damage
- Reading the chip with a flash reader to dump its contents to a file; each manufacturer stores data with different parameters, so the blocks and banks have to be identified correctly
- Processing that raw data with specialist tools to reassemble the data and rebuild a file system from which files can be copied — by far the longest and most complex stage, because every card differs in memory type and controller
- Verifying the recovered files and returning them to the client on sound media
Does recovery reduce quality?
No. In the great majority of cases, recovering photographs from a memory card or USB stick does not affect them at all — the image or audio quality is exactly as it was.
The single most important thing
Stop using the card. Flash media reuses freed space aggressively, so continuing to shoot or write to a card after a deletion is the fastest way to make the data unrecoverable.