Memory Copyback Data Path Selection with Adaptive RBER Thresholds
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Solution Overview
Problem
Conventional memory sub-systems face challenges in balancing latency and reliability due to varying raw bit error rates (RBER) across the drive life of a memory device, particularly in non-volatile memory devices like QLC, as they typically use a fixed RBER threshold for data path selection during copyback operations.
Innovation Solution
Implementing an adaptive data path selection threshold in memory sub-systems that adjusts RBER thresholds based on program-erase cycle (PEC) ranges, using look-up tables to determine optimal thresholds for different PEC stages, thereby balancing latency and reliability by selecting appropriate data paths with ECC decoding or direct data transfer based on RBER comparisons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed RBER threshold is used for data path selection during copyback operations, then the system maintains consistent decision-making criteria, but it cannot adapt to varying error rates across the drive life, resulting in suboptimal performance balancing between latency and reliability
Solution Approach 1:
The patent implements dynamic threshold adjustment by transitioning from a fixed RBER threshold to multiple adaptive thresholds selected based on program-erase cycle ranges. The threshold is no longer static but changes dynamically according to the memory device's operational stage, allowing the system to adapt to varying error rates throughout the drive life while maintaining manageable complexity through structured threshold selection criteria
Solution Approach 2:
The patent changes the parameter of the RBER threshold from a fixed value to multiple variable thresholds corresponding to different program-erase cycle ranges. By modifying the threshold parameter based on the operational stage of the memory device, the system achieves adaptability to varying error rates without excessive complexity, as the parameter change follows predictable patterns tied to device usage
2Speed
If higher RBER thresholds are used at the beginning of drive life, then latency is reduced through faster data transfer, but reliability may be compromised when error rates increase at the end of drive life
Solution Approach 1:
The patent applies dynamic threshold adjustment to balance speed and reliability throughout the drive life. By selecting different RBER thresholds based on program-erase cycle ranges, the system maintains higher thresholds (faster transfer) when error rates are low and switches to lower thresholds (slower but more reliable transfer) when error rates increase, achieving adaptive optimization of both speed and reliability
Solution Approach 2:
The patent changes the RBER threshold parameter based on the operational stage to optimize the trade-off between speed and reliability. At the beginning of drive life, higher thresholds enable faster data transfer, while at the end of drive life, lower thresholds enhance reliability. This parameter adaptation allows the system to optimize performance characteristics according to actual device conditions
3Reliability
If lower RBER thresholds are used at the end of drive life, then reliability is enhanced through more conservative data path selection, but latency increases due to additional ECC decoding operations
Solution Approach 1:
The patent uses dynamic threshold selection based on program-erase cycle ranges to manage the reliability-latency trade-off. By lowering the RBER threshold at the end of drive life when error rates increase, the system prioritizes reliability through more conservative data path selection, accepting increased latency as a necessary compromise for maintaining data integrity in degraded device conditions
Data Source
AI summary
An example method includes: identifying using a look-up table, a threshold raw bit error rate (RBER) corresponding to a current program-erase cycle (PEC) count of a first block of the memory device; determining a RBER value associated with data of a second block of the memory device; determining whether the RBER value associated with the data of the second block is less than or equal the threshold RBER; and in response to determining that the RBER value is less than or equal the threshold RBER, writing the data of the second block to the first block.