Hybrid Bitmap Counter System for NAND Flash Storage
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Solution Overview
Problem
Conventional storage device counter systems are inefficient in space usage, overly complex, and inadequate in protecting operating data, particularly in tracking Program/Erase cycles in NAND flash storage devices, leading to issues such as high storage requirements and potential data loss during power failures.
Innovation Solution
A hybrid value field/bitmap field counting technique is implemented, where a counter management engine resets and updates bitmaps in non-volatile memory, converting values when bitmap fields are filled, and maintains redundant data across two counters to reduce storage needs and ensure data integrity during power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional down counter technique is used to track P/E cycles, then the operating data can be tracked, but the storage space required becomes excessively large (2 MB for a 4 TB SSD)
Solution Approach 1:
The patent divides the counter storage into multiple superblocks, where each superblock contains a subset of the total counter data. This segmentation allows the system to manage and store counter information in distributed units rather than a single large structure, reducing the impact of any single point of failure and improving space utilization efficiency.
Solution Approach 2:
The patent changes the data representation parameter from storing full P/E cycle counts to storing only the least significant bits (LSBs) of the counter values. This parameter change dramatically reduces the storage space required while maintaining the ability to track operating data, as only the changing bits need to be stored rather than the entire counter value.
2Measurement precision
If a digital counter technique is used to save P/E cycle values, then the counter accuracy is maintained, but the system complexity increases significantly
Solution Approach 1:
The patent extracts only the necessary portion of the counter data (the least significant bits that change with each P/E cycle) and stores only that information. By taking out only the essential changing data rather than storing complete counter values, the system maintains measurement precision for tracking purposes while dramatically simplifying the storage and management structure.
Solution Approach 2:
The patent creates simplified copies of the counter information by storing only the LSBs in a compact bitmap format. This copying approach maintains the essential tracking capability while reducing complexity, as the bitmap structure is much simpler to manage than full digital counter values.
3Quantity of substance
If counter data is stored in a single location, then the storage efficiency is high, but the data protection against power failure and corruption is insufficient
Solution Approach 1:
The patent implements beforehand cushioning by creating redundant copies of the counter data distributed across multiple superblocks before any potential data loss can occur. This proactive redundancy ensures that if power failure or corruption affects one location, the data remains protected through pre-established backup copies in other superblocks.
Solution Approach 2:
The patent creates multiple copies of the counter data distributed across different superblocks. This copying strategy ensures that the original data is preserved even if one copy is lost due to power failure or corruption, thereby improving reliability without significantly impacting storage efficiency.
Data Source
AI summary
A counter system includes a counter management subsystem, a storage subsystem having storage elements, and a non-volatile memory system storing a first counter including a first value field/first bitmap field combination for each storage element, and a second counter including a second value field/second bitmap field combination for each storage element. The counter management subsystem resets the first counter and, following each storage operation on a storage element, updates a bit in the first bitmap field for that storage element. When one of the first bitmap fields is filled, the counter management subsystem converts each first value field/first bitmap field combination to a respective first value, resets the second counter, updates the second value field for each storage element with the respective first value for each storage element and, following each storage operation on a storage element, updates a bit in the second bitmap field for that storage element.