Storage Device Read Reclaim Using Sample Voltage Estimation
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Solution Overview
Problem
The reliability of data stored in nonvolatile memory devices decreases over time, leading to potential data loss, and existing solutions do not effectively address the degradation of data reliability during read operations.
Innovation Solution
A storage device with a controller that performs sample read operations using different voltages to estimate read counts and determine optimal locations for writing data in a second storage area, ensuring robustness against degradation by relocating data from a first storage area to a second storage area based on these estimates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is continuously stored in the same location in nonvolatile memory, then storage capacity is maximized, but data reliability decreases over time due to degradation
Solution Approach 1:
The controller performs sample read operations with different read voltages before the actual read reclaim operation to estimate read counts and predict data degradation. This preliminary assessment allows the system to proactively identify data that needs relocation before reliability issues manifest, preventing data loss rather than reacting to it.
Solution Approach 2:
The system changes read voltage parameters during sample read operations to estimate read counts accurately. By applying different read voltages and analyzing the results, the controller can determine which data has been read frequently and is therefore more susceptible to degradation, enabling targeted relocation decisions based on actual usage patterns rather than uniform treatment of all data.
2Reliability
If read reclaim operations are performed frequently to maintain data reliability, then data integrity is improved, but system performance and productivity decrease
Solution Approach 1:
Instead of uniformly applying read reclaim operations to all stored data, the system identifies specific data regions that require relocation based on their read history and degradation risk. The controller relocates only the necessary portions of data that show signs of degradation, leaving other data in place, thereby minimizing the performance impact while maintaining data integrity for critical regions.
Solution Approach 2:
The system uses the memory device's own read operations and voltage characteristics to automatically identify which data needs relocation. By monitoring the device's intrinsic behavior during normal read operations, the controller can autonomously determine degradation patterns and trigger selective read reclaim operations without requiring external intervention or comprehensive system pauses.
3Measurement precision
If sample read operations with multiple voltages are performed to estimate read counts, then data relocation accuracy is improved, but operation time and energy consumption increase
Solution Approach 1:
The controller performs a limited number of sample read operations with different voltages on selected data regions rather than exhaustively testing all data. This partial action approach provides sufficient information to identify high-risk data for relocation without the time and energy cost of complete analysis, achieving an optimal balance between measurement precision and operational efficiency.
Data Source
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AI summary
Described is a storage device that includes a nonvolatile memory device that includes a first storage area and a second storage area. A controller of the storage device controls the nonvolatile memory device and performs a read reclaim operation of reading data stored in the first storage area of the nonvolatile memory device and writing the read data in the second storage area. In the read reclaim operation, the controller is further configured to allow the nonvolatile memory device to perform sample read operations on the first storage area and to determine locations of the second storage area, at which the data are to be written, based on results of the sample read operations.