Flash Memory Bad Block Management via Pseudo-Bad Block Recollection
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Solution Overview
Problem
Flash memory units can become unusable due to manufacturing defects or operational errors, leading to 'bad blocks' that deplete the reserved area, causing the flash memory to wear out, and the failure of bad block management tables compromises replacement mechanisms.
Innovation Solution
A method and apparatus for bad block management that recollects pseudo-bad blocks from both the reserved and user areas by erasing and re-evaluating their states, and a mechanism to store and backup bad block management tables across a wider range of blocks to ensure reliability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If blocks of the reserved area are used to replace bad blocks of the user area, then the reliability of storage is improved, but the duration of action of the flash memory deteriorates as the reserved area depletes
Solution Approach 1:
The patent recovers pseudo-bad blocks by attempting to erase and reuse blocks that were previously marked as bad. When a bad block is encountered, the system attempts to erase it and verify if it becomes functional again. Successfully recovered blocks are added back to the pool of usable blocks, extending the flash memory's operational life without compromising storage reliability.
2Device complexity
If bad block management tables are stored in a limited range of blocks, then the device complexity is reduced, but the reliability deteriorates as single point of failure increases
Solution Approach 1:
The patent distributes the bad block management table across multiple blocks within a restricted area rather than concentrating it in a single location. Each block in the restricted area can store portions of the management table, creating redundancy. If one block fails, the system can retrieve management information from other blocks, significantly improving reliability while maintaining relatively simple device structure.
3Measurement precision
If all bad blocks are permanently marked and excluded from use, then the measurement precision of block status is improved, but the productivity deteriorates due to loss of usable storage space
Solution Approach 1:
The patent implements a dynamic bad block management system where block status is not fixed but can change over time. Blocks marked as bad can be re-evaluated and potentially recovered through erase operations. The system continuously updates the bad block management table based on current block states, allowing previously bad blocks to become usable again, thereby improving storage efficiency while maintaining accurate block status tracking.
Data Source
AI summary
A method of managing blocks in a flash memory includes: detecting states of blocks of a reserved area in the flash memory and building a bad block management table accordingly; recording mappings between bad blocks of an user area in the flash memory and good blocks of the reserved area into the bad block management table; when the bad block management table indicates there is no good block remaining in the reserved area that can be mapped to, selecting one of bad blocks of the reserved area or the user area and obtaining a recollected block after erasing the selected bad block; recording a mapping between the recollected block and a bad block in the user area into the bad block management table; and based on the bad block management table, programming data into the recollected block.