Delta Checkpoints for Non-Volatile Memory Indirection Table Recovery
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Solution Overview
Problem
Recreating an indirection table for non-volatile memory after a power loss event can take a considerable amount of time, especially for large NAND storage elements, and periodic saving of the entire indirection table degrades system performance and affects Quality of Service (QoS).
Innovation Solution
Implementing a delta checkpoint system that logs updates to the indirection table, allowing for the recovery of the table based on delta information instead of re-reading all metadata pages, reducing the need to read every NAND page and incorporating a bitmask to determine which erase blocks need re-erasure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the entire indirection table is periodically saved to non-volatile memory, then data reliability is improved, but system performance and Quality of Service deteriorate
Solution Approach 1:
The indirection table is divided into multiple erase blocks, with only the modified portions (delta checkpoints) being saved to non-volatile memory. This segmentation allows the system to maintain data reliability by persisting critical changes while avoiding the performance penalty of saving the entire table, thus resolving the contradiction between reliability and productivity.
Solution Approach 2:
The patent extracts only the essential delta checkpoint information (metadata and logical-to-physical address mappings) from the complete indirection table for periodic saving. By taking out only the necessary portions rather than the entire table, the system achieves reliable data persistence without degrading system performance, thereby resolving the contradiction between reliability and productivity.
2Reliability
If the entire indirection table is recreated after a power loss event, then data reliability is improved, but recovery time increases
Solution Approach 1:
The system performs preliminary actions by periodically saving delta checkpoint information to non-volatile memory before power loss events occur. This preliminary caching of essential indirection table data in non-volatile memory enables rapid recovery after power loss, as the system can restore from the most recent checkpoint rather than recreating the entire table, thus resolving the contradiction between reliability and recovery time.
Solution Approach 2:
The patent creates a simplified copy (delta checkpoint) of the indirection table containing only the essential metadata and address mappings needed for recovery. This copy is periodically saved to non-volatile memory, enabling fast restoration of data reliability after power loss without requiring time-consuming recreation of the complete indirection table, thereby resolving the contradiction between reliability and recovery time.
3Loss of time
If delta checkpoint information is saved frequently, then power fail recovery time is reduced, but runtime latency increases
Solution Approach 1:
The system implements periodic saving of delta checkpoint information to non-volatile memory at predetermined intervals rather than after every modification. This periodic action strikes a balance between reducing power fail recovery time (by having recent checkpoints available) and minimizing runtime latency (by not forcing writes on every indirection table update), thus resolving the contradiction between recovery time and runtime latency.
Data Source
AI summary
According to some embodiments, delta checkpoints are provided for a non-volatile memory indirection table to facilitate a recovery process after a power loss event.