NAND Flash Page Relocation Based on Hard Error Tracking
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Solution Overview
Problem
Existing non-volatile memory devices face challenges in maintaining data integrity due to high hard error percentages, which degrade the performance of low-density parity-check (LDPC) decoders, especially in multi-level cell NAND flash memory, leading to increased codeword failure rates.
Innovation Solution
Implementing a data relocation strategy based on tracking hard errors, using both failed bit count and hard error percentage, to proactively relocate data from affected pages to spare pages, thereby reducing overall hard error rates and improving decoder performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is stored in non-volatile memory devices with high hard error percentages, then storage capacity is maintained, but data integrity and decoder performance deteriorate
Solution Approach 1:
The system performs preliminary tracking of hard errors using a hard error tracker before decoder performance degrades. By monitoring hard error percentages and failed bit counts in advance, the system can proactively relocate data from pages with deteriorating memory cells to healthy pages, preventing decoder performance degradation while maintaining storage capacity
Solution Approach 2:
The system implements a feedback mechanism where the hard error tracker continuously monitors error rates and provides information to the data relocation logic. Based on this feedback about hard error percentages and failed bit counts, the system dynamically decides when and where to relocate data, creating a closed-loop control system that maintains data integrity while preserving decoder performance
2Reliability
If data relocation is performed frequently to maintain data integrity, then reliability improves, but system complexity and overhead increase
Solution Approach 1:
The system changes the parameters used for relocation decisions from simple error counts to a composite metric that includes both hard error percentages and failed bit counts. This parameter transformation allows the system to set threshold-based relocation triggers that balance reliability improvement with manageable complexity, avoiding overly frequent relocations while maintaining data integrity
Solution Approach 2:
The memory device is segmented into multiple pages, and the hard error tracker monitors each page independently. This segmentation allows the data relocation logic to selectively relocate data only from affected pages rather than performing full-page or device-wide relocations, reducing the complexity and overhead of memory management operations
3Reliability
If hard error tracking and data relocation are implemented, then data integrity improves, but processing time and latency increase
Solution Approach 1:
The hard error tracking and data relocation operations are performed in advance during background processing or idle periods, before data retrieval is needed. This preliminary action ensures that when data needs to be retrieved, it is already in its optimal location with minimal errors, eliminating the need for time-consuming error correction or re-retrieval operations
Solution Approach 2:
The hard error tracker operates continuously in the background, monitoring error rates without interrupting normal read/write operations. This continuous monitoring allows the system to maintain up-to-date error information without adding significant processing overhead to data retrieval operations, as the tracking occurs concurrently with other memory operations
Data Source
AI summary
Devices, systems, and methods for improving performance of an iterative decoder in a non-volatile memory are described. An example method includes obtaining a hard error percentage, a spare byte percentage, and a total error count associated with a first page in the memory device, determining that the total error count is greater than a threshold value that is determined based on the hard error percentage and the spare byte percentage, and performing, based on the determining, a data relocation operation that relocates at least some data from the first page to a second page different from the first page.