SSD Two-Stage Power-On Map Rebuild with S-Journal
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Solution Overview
Problem
Conventional SSDs face inefficiencies in data storage and retrieval due to the large size of the Logical-to-Physical (L2P) map table, which requires frequent updates and rebuilds upon power loss, leading to delayed system readiness and increased write amplification.
Innovation Solution
The implementation of a System Journal (S-Journal) and a two-stage power-on map rebuild process, where S-Journals store physical-to-logical address correspondences and reduce the need to save the entire L2P map table, allowing for incremental updates and efficient garbage collection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large L2P map table is used to map all logical blocks to physical locations, then complete address mapping is achieved, but the time required to rebuild the map table upon power loss increases significantly
Solution Approach 1:
The L2P map table is divided into multiple sections, each stored in separate non-volatile memory locations. Only the necessary sections are rebuilt upon power loss, rather than reconstructing the entire map table, thereby reducing power-on readiness time while maintaining complete address mapping capability
Solution Approach 2:
The system performs preliminary actions by maintaining a journal that records changes to the L2P map table in real-time. Upon power loss, the journal is used to reconstruct only the modified sections of the map table, avoiding the need to rebuild the entire table and significantly reducing power-on readiness time
2Reliability
If the entire L2P map table is saved frequently to non-volatile memory, then data integrity is maintained, but write amplification increases
Solution Approach 1:
The system extracts and stores only the changed portions of the L2P map table in a journal structure, rather than saving the entire map table. This selective extraction approach maintains data integrity by recording all necessary changes while minimizing the amount of data written to non-volatile memory, thereby reducing write amplification
Solution Approach 2:
Instead of performing excessive actions by saving the complete L2P map table, the system performs partial actions by saving only the modified sections through journaling. This partial action approach ensures data integrity for changed entries while significantly reducing the write volume to non-volatile memory
Data Source
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AI summary
A data storage device comprises a non-volatile memory comprising a plurality of blocks, each configured to store a plurality of physical pages at predetermined physical locations. A controller programs and reads data stored in a plurality of logical pages. A volatile memory comprises a logical-to-physical address translation map configured to enabling determination of the physical location, within one or more physical pages, of the data stored in each logical page. A plurality of journals may be stored, each comprising a plurality of entries associating one or more physical pages to each logical page. At startup, the controller may read at least some of the plurality of journals in an order and rebuild the map; indicate a readiness to service data access commands after the map is rebuilt; rebuild a table from the map and, based thereon, select block(s) for garbage collection after having indicated the readiness to process the commands.