LBA/PBA Table Rebuild Using Bitmap-Skipped Metadata Scans
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Solution Overview
Problem
The large storage capacity of flash memory devices in SSDs makes it difficult for solid state drives to recover from power failures due to insufficient space in local memory to rebuild the LBA/PBA table, requiring multiple scans of meta data, which consumes significant time and delays recovery.
Innovation Solution
A bitmap is used to identify unmapped PBA groups, allowing the controller to skip reading irrelevant meta data during the LBA/PBA table rebuild, reducing the number of scans needed and accelerating the reconstruction process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple scans of metadata are performed to rebuild the LBA/PBA table, then the table can be reconstructed, but the recovery time is significantly extended
Solution Approach 1:
The patent maintains a bitmap in memory during normal operation that pre-records which PBA groups are mapped to LBAs. Upon power failure, this bitmap is immediately used to identify which metadata regions contain valid mappings, allowing the rebuild process to skip unmapped regions entirely. This preliminary preparation of the bitmap structure enables rapid recovery by avoiding unnecessary scans of metadata that cannot contain relevant mapping information.
2Reliability
If all metadata is scanned during LBA/PBA table rebuild, then complete coverage is achieved, but processing overhead increases significantly
Solution Approach 1:
The patent extracts and utilizes the mapping status information stored in the bitmap structure, separating the identification of relevant metadata regions from the actual scanning process. By extracting this metadata about metadata (the bitmap indicating which PBA groups are mapped), the system can selectively process only the necessary portions of the actual metadata, eliminating redundant processing of unmapped regions while ensuring complete coverage of all mapped mappings.
Data Source
AI summary
A method is described. The method includes constructing a bitmap having a first dimension organized into bins of logical block addresses (LBA bins) and a second dimension organized into bins of physical block addresses (PBA bins). Coordinates of the bitmap indicate whether respective physical blocks of non volatile memory within one or more SSDs that fall within a particular PBA bin are being mapped to by an LBA that falls within a particular one of the LBA bins. The method includes using the bitmap during a rebuild of an LBA bin of an LBA/PBA table to avoid reading meta data for physical blocks that are not mapped to by an LBA that falls within the LBA bin.