SSD LBA/PBA Table Rebuild Using Bitmap-Based Metadata Skipping
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Solution Overview
Problem
The large storage capacity of flash memory devices in solid state drives (SSDs) complicates the recovery from power failures due to insufficient space in local memory to rebuild the LBA/PBA table, necessitating 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 time required for reconstruction by avoiding unnecessary data processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple scans of meta data 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 data structure that pre-records the mapping relationships between LBA bins and PBA bins during normal operation. When power failure occurs, this pre-prepared bitmap allows the system to immediately identify which PBA bins contain valid data without scanning all meta data, thus applying preliminary action to avoid time-consuming full scans during recovery
Solution Approach 2:
The patent extracts only the necessary information (mapping relationships) from the complete meta data and stores it in a compact bitmap structure. During recovery, instead of scanning all meta data, the system only needs to query the bitmap to identify relevant PBA bins, effectively taking out only the essential information needed for reconstruction
2Loss of information
If all meta data is scanned to ensure complete LBA/PBA table recovery, then no mapping information is lost, but the processing time and computational resources increase significantly
Solution Approach 1:
The patent applies partial action by scanning only the necessary portions of meta data identified through the bitmap, rather than performing excessive full scans of all meta data. The bitmap guides the system to process only relevant PBA bins, achieving complete recovery of valid mappings without the overhead of processing irrelevant data
3Quantity of substance
If the SSD storage capacity is expanded, then more data can be stored, but the complexity of maintaining and recovering the LBA/PBA table increases
Solution Approach 1:
The patent introduces a bitmap data structure as an additional dimension layer between the LBA/PBA table and the underlying meta data. This bitmap layer organizes mapping information in a compact, addressable format that scales efficiently with storage capacity, transforming the complexity from linear scanning of large meta data sets to efficient bitmap-based address lookup
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.