Adaptive Read Disturb Reclaim Policy for Flash Memory
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Solution Overview
Problem
Current memory systems fail to accurately predict when to reclaim data from flash memory due to uneven error count increase per read disturb, especially under varying P/E cycles, leading to uncorrectable errors and data loss, as they assume a uniform error growth that is not true for flash memory under different P/E cycles.
Innovation Solution
Implementing a memory system with a first counter that increments with each read and a second counter that tracks the number of times the first counter reaches a predefined count, determining an error count, and initiating a reclaim function when the error count exceeds a threshold, allowing for more accurate prediction of when to reclaim data before errors become uncorrectable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a uniform error growth assumption is used for flash memory, then the reclaim policy is simple to implement, but data loss occurs due to inaccurate prediction of when to reclaim
Solution Approach 1:
The patent changes the parameter from a uniform error growth assumption to a variable error growth model that adapts to different P/E cycles. The controller now tracks actual error counts and adjusts reclaim thresholds dynamically based on observed error patterns across multiple P/E cycles, resolving the contradiction between simplicity and accuracy.
Solution Approach 2:
The patent introduces feedback mechanisms where the controller monitors actual error counts during read operations and uses this information to adjust future reclaim decisions. By comparing predicted vs. actual error growth, the system refines its reclaim timing predictions, improving data retention accuracy while maintaining manageable complexity through iterative learning.
2Reliability
If reclaim is performed too early based on uniform error growth assumption, then data loss is prevented, but storage capacity is wasted due to premature reclamation
Solution Approach 1:
The patent dynamically adjusts the reclaim threshold parameter based on actual error growth patterns observed across different P/E cycles. Instead of using a fixed threshold based on uniform growth assumptions, the system adapts the threshold to match the actual non-uniform error growth characteristics of the flash memory, preventing both premature and delayed reclamation.
3Speed
If read operations are frequently performed on the same block, then data access speed is improved, but error count increases leading to potential data loss
Solution Approach 1:
The patent implements feedback tracking of read operations per block, where the controller monitors both the frequency of reads and the resulting error counts. This feedback allows the system to identify blocks that are being read frequently and adjust reclaim timing proactively, preventing data loss while allowing optimal read performance.
Solution Approach 2:
The patent performs preliminary error checking and proactive reclaim operations on blocks that show signs of frequent reading. By detecting increased read frequency and potential error accumulation early, the system can initiate reclaim before errors become uncorrectable, preserving data integrity without limiting read access speed.
Data Source
AI summary
Memory systems may include a memory including a plurality of memory blocks, and a controller suitable for, incrementing a first counter corresponding to a block of the plurality of blocks when the block is read, incrementing a second counter when the first counter reaches a predefined count number, determining an error count of the block when the second counter is incremented, and initiating a reclaim function when the error count exceeds an error threshold.