Bad Block Management
Bad Block Management is a mechanism used by the controller in flash memory to detect and handle bad blocks. It identifies and marks defective blocks, ensuring they are not used for data storage again. To maintain data reliability, the controller replaces bad blocks with reserved spare blocks, which helps prevent data corruption and improves the overall reliability and lifespan of the memory.
Bad blocks in flash memory are categorized into two types:
- Early Bad Blocks: These are defects that occur during the manufacturing process.
- Later Bad Blocks: These develop over time due to wear and tear from repeated write and erase operations.
When flash memory is used for the first time, the controller's built-in program creates a bad block table, recording the locations of bad blocks to prevent future use. If a block becomes unusable, the controller first applies Error Correction Code (ECC) to attempt recovery. If ECC fails, the controller migrates the valid data to a new, healthy block to avoid data loss.
To support this process, around 7% of the flash memory's capacity is reserved as spare blocks, ensuring seamless replacement of bad blocks and maintaining consistent performance.
