Solid State Memory End of Life Extension via Error Tracking
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Solution Overview
Problem
Solid state memory devices, such as NAND flash memory, face limitations in operational life due to wear and tear, leading to increased read errors as they approach the end of life (EOL) condition, necessitating effective management to extend their lifespan and ensure reliable data retrieval.
Innovation Solution
A control circuit maintains a data structure tracking readback error rates and erasure counts, retiring memory locations from service when they reach EOL, using an exception list to identify and rehabilitate or retire pages with high error rates, thereby extending the memory's operational life and maintaining acceptable read error rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If memory locations are continuously used beyond the specified end of life (EOL) condition, then the productivity and utilization of the memory device is improved, but the reliability deteriorates due to increased read errors and wear
Solution Approach 1:
The memory device is segmented into active memory locations and retired memory locations. The controller maintains a data structure that divides the memory space, allowing healthy locations to remain productive while isolating worn-out locations that exhibit high read error rates. This segmentation enables continued utilization of functional memory regions while excluding degraded regions.
Solution Approach 2:
The system changes the operational status parameter of memory locations from active to retired based on monitored read error rates and erasure counts. By dynamically adjusting the可用性 parameter of memory locations based on their degradation state, the system maintains overall reliability while maximizing the utilization of healthy memory regions.
2Productivity
If memory locations with high read error rates are continued to be used, then the productivity is improved, but the reliability deteriorates due to data retrieval errors
Solution Approach 1:
The controller implements a feedback mechanism by monitoring read error rates for each memory location and using this information to determine when to retire locations. The data structure stores error rate information that feeds back into the retirement decision process, allowing the system to respond to degradation and maintain data retrieval reliability while preserving usable capacity.
Solution Approach 2:
The system treats individual memory locations as disposable units that can be retired when they reach their operational lifespan. By retiring individual faulty locations rather than the entire memory device, the system discards only the degraded portions while maintaining the functionality and capacity of healthy locations.
3Reliability
If the memory device is retired at the specified end of life (EOL) condition, then the reliability is maintained, but the productivity is reduced due to premature retirement
Solution Approach 1:
The system applies local quality management by treating each memory location independently with its own quality assessment based on read error rates. Rather than retiring the entire device at a uniform EOL threshold, the system maintains local quality control, allowing individual locations to be retired based on their specific degradation state while others continue operating.
Solution Approach 2:
The controller performs preliminary actions by monitoring and tracking read error rates before actual failures occur. By proactively identifying locations that are approaching degradation thresholds and retiring them preemptively, the system prevents reliability deterioration while extending the overall operational lifespan of the memory device.
4Device complexity
If no exception list is maintained, then the device complexity is reduced, but the reliability deteriorates due to inability to identify and retire faulty pages
Solution Approach 1:
The exception list serves as an intermediary data structure that mediates between the physical memory locations and the controller's retirement decisions. This intermediate structure stores error rate information and facilitates the identification of faulty pages without requiring complex real-time analysis during normal operations, thus balancing reliability management with acceptable device complexity.
Data Source
AI summary
Method and apparatus for managing a solid state memory, such as but not limited to a NAND flash memory. In some embodiments, a storage device includes a non-volatile solid state memory and a control circuit configured to transfer user data between the memory and a host device. The control circuit maintains, in a local memory, a data structure indicative of measured readback error rates associated with memory locations in the memory in relation to erasure counts associated with the memory locations. The control circuit retires a subset of the memory locations identified by the data structure from further availability to store user data from the host device responsive to the measured readback error rates, and responsive to the erasure counts of said memory locations indicating the memory has reached an end of life (EOL) condition.