SSD NAND Read Retry Using Aging-Based Voltage Selection
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Solution Overview
Problem
Flash memory in SSDs experiences degradation due to charge loss, leading to bit read errors, which conventional read retry processes address inefficiently, causing prolonged processing times and potential system failures.
Innovation Solution
An adaptive read retry process using a pattern of retry voltage index sets determined by an aging parameter of the SSD, such as P/E cycles, temperature, or elapsed time, to quickly and efficiently compensate for charge loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional read retry processes are used to address charge loss, then bit read errors can be corrected, but processing time increases and system reliability decreases
Solution Approach 1:
The system performs preliminary actions by determining the aging parameter (P/E cycles, temperature, or elapsed time) before initiating the read retry process. This preliminary determination allows the system to select the appropriate voltage index set in advance, avoiding unnecessary trial-and-error read attempts and reducing processing time while maintaining data read accuracy.
Solution Approach 2:
The system dynamically adjusts the read retry process by selecting different voltage index sets based on the determined aging parameter. Instead of using a fixed read retry sequence, the voltage indices are adapted dynamically according to the specific degradation conditions, optimizing both processing speed and data recovery accuracy.
2Reliability
If sequential voltage index sets are used for read retry, then comprehensive coverage of degradation scenarios is achieved, but computational resource usage increases
Solution Approach 1:
The system changes the parameter of voltage index selection based on the aging parameter determination. By mapping the aging parameter (P/E cycles, temperature, or elapsed time) to specific voltage index sets, the system avoids exhaustively testing all possible voltage combinations, thereby reducing computational resource usage while maintaining comprehensive coverage of degradation scenarios.
Solution Approach 2:
The system uses feedback from the aging parameter determination to guide the voltage index selection process. The determined aging parameter provides feedback that directs the system to the most appropriate voltage index set, avoiding unnecessary computational attempts and optimizing resource usage.
3Reliability
If multiple read retry attempts are performed, then data recovery from degraded memory is improved, but system crashes may occur due to prolonged processing
Solution Approach 1:
The system performs preliminary determination of the aging parameter before initiating read retry attempts. This preliminary action enables the system to select the most appropriate voltage index set in advance, reducing the number of necessary retry attempts and minimizing processing time while maintaining effective data recovery capability.
Solution Approach 2:
The system dynamically adapts the read retry process based on the aging parameter, selecting optimal voltage index sets that maximize data recovery probability while minimizing the number of attempts required. This dynamic approach prevents prolonged processing that could lead to system crashes.
Data Source
AI summary
A method of operating a computing device with a solid state drive (SSD) includes: obtaining a preexisting read retry table that includes a sequential list of voltage index sets for reading a flash memory of the SSD; determining an aging parameter of the SSD; identifying a retry voltage index set from the sequential list based on the aging parameter; and reading the flash memory using the retry voltage index set.