FlashDisk Bad Block Management

Introduction

Bad blocks are blocks that contain one or more invalid bits whose reliability is not guaranteed. Bad blocks may be present when the device is shipped, or may develop during the lifetime of the device.
Devices with bad blocks have the same quality level and the same AC and DC characteristics as devices where all the blocks are valid. A bad block does not affect the performance of valid blocks because it is isolated from the bit line and common source line by a select transistor.

As the failure of a page program operation does not affect the data in other pages in the same block, the block can be replaced by re-programming the current data and copying the rest of the replaced block to an available valid block.

FlashDisk BBM

FlashDisk implements the Bad Block Management in the Flash Translation Layer (FTL), not in the FMD layer. In FlashDisk, some good blocks are reserved for garbage collection and for replacing the runtime bad blocks.