Wear Leveling Controller Using Elapsed Time and Write Count
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Solution Overview
Problem
Data storage devices with nonvolatile memory face challenges in extending the service lifetime due to wear and tear, particularly from the drift phenomenon where resistance values of memory cells increase over time, leading to read errors if not addressed.
Innovation Solution
A data storage device with a controller that monitors elapsed time and write count, performing a wear leveling operation using algorithms like swap or gap algorithms to redistribute data across memory units, ensuring all data is rewritten within a critical time frame set based on drift time, thereby preventing error bits and extending service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wear leveling operation is performed frequently to prevent drift phenomenon, then data reliability is improved, but controller operational burden increases
Solution Approach 1:
The patent changes the triggering parameters for wear leveling operations from traditional write-count-based metrics to a dual-parameter system incorporating both elapsed time and write count. This allows the controller to perform wear leveling operations based on drift time thresholds, preventing the drift phenomenon while optimizing the frequency of operations to reduce unnecessary controller overhead.
Solution Approach 2:
The patent implements preliminary wear leveling operations before the drift phenomenon actually occurs by monitoring elapsed time against a predetermined drift time threshold. This proactive approach rewrites data in memory units before resistance values increase to erroneous levels, preventing read errors while managing controller workload through scheduled operations rather than reactive interventions.
2Device complexity
If wear leveling operation is delayed to reduce controller burden, then operational complexity decreases, but read errors occur due to drift phenomenon
Solution Approach 1:
The patent implements a feedback mechanism where the controller continuously monitors both elapsed time and write count parameters, comparing them against predetermined thresholds (drift time and critical write count). This feedback loop ensures wear leveling operations are triggered at the optimal moment - before drift causes read errors but without excessive operational complexity, as the system automatically manages the timing based on monitored parameters.
3Reliability
If data is rewritten early to prevent drift, then data reliability is improved, but write operations increase reducing productivity
Solution Approach 1:
The patent applies partial wear leveling operations by selecting only specific memory units that meet the drift time or write count thresholds for rewriting, rather than performing full memory rewrites. This selective approach prevents drift-induced read errors in critical memory units while minimizing unnecessary write operations on already healthy memory units, thus maintaining data integrity without excessive productivity loss.
Data Source
AI summary
A data storage device includes a nonvolatile memory device including a memory region, the memory region including a plurality of memory units; and a controller suitable for monitoring an elapsed time and a write count of the memory region, and performing a wear leveling operation for at least one memory unit selected among the plurality of memory units depending on a monitoring result.