Management of bad blocks
Management of bad blocks
The flash memory module consists of many blocks, which can be classified as good blocks and bad blocks.
Good blocks can be used to store, read and write data. Bad blocks should not be used. There are two types of bad blocks.
One is called "original bad block" and the other one is called "damaged bad blocks".
Original bad blocks are labelled during the production of NAND flash memory.
Damaged bad blocks are originally good but labelled damaged after use. For example,
if errors are caused during writing or erasing, or if error correction code (ECC) errors are caused during reading.
The management of bad blocks refers to that the bad blocks are "switched" to a good block when the machine is accessing the data. That is to say, these bad blocks are replaced. Therefore, the machine can access the whole logic area without having any errors.
During the production process, original bad blocks will be re-mapped into the reserved good blocks. The damaged bad blocks will be processed later. If the bad blocks are found in the flash memory during the use, the controller will find a reserved good block to replace the bad one. If all reserved good blocks are used for replacement, this flash memory module will be forced into the read-only mode.