Solid-State Storage Weak Erase Failure Detection and Mitigation
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Solution Overview
Problem
Solid-state storage devices face challenges with 'weak erase' failures, which can result in uncorrectable errors and negatively impact performance, as existing technologies struggle to detect and mitigate these failures effectively, especially when they do not involve erase or program errors.
Innovation Solution
A method is developed to detect permanent failures causing 'weak erase' failures by comparing an erase fail bits metric to a predefined threshold, and mitigate these failures by changing the status of affected cells to a defective or retired state, employing techniques like infant mortality screening, wear-induced mitigation, double erase fix, and page calibration to prevent data loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If weak erase failures are not detected and mitigated, then storage device operates without intervention, but uncorrectable errors occur and performance deteriorates
Solution Approach 1:
The patent applies preliminary action by performing infant mortality screening during factory testing to identify and isolate cells with weak erase characteristics before they cause failures in production. This proactive detection and isolation of defective cells prevents subsequent uncorrectable errors without requiring complex real-time intervention systems during normal operation.
Solution Approach 2:
The patent implements feedback mechanisms through wear-induced mitigation where the storage device monitors erase failure rates and automatically adjusts mitigation strategies based on observed failure patterns. This closed-loop feedback system enables dynamic adaptation to changing failure conditions, improving reliability while managing system complexity through data-driven decision making.
2Measurement precision
If erase fail bits metric comparison is used to detect permanent failures, then weak erase failures can be identified, but detection accuracy must be maintained without false positives
Solution Approach 1:
The patent applies parameter changes by establishing dynamic thresholds for erase fail bits that adapt to different storage conditions and failure modes. The system adjusts detection parameters based on the specific characteristics of weak erase failures versus normal operation, enabling precise differentiation between acceptable variations and actual failures, thereby reducing false positives while maintaining high detection accuracy.
3Reliability
If affected cells are changed to defective or retired state, then data loss is prevented, but storage capacity is reduced
Solution Approach 1:
The patent applies segmentation by isolating defective cells at the page or block level rather than affecting the entire storage device. This localized isolation of cells with weak erase characteristics allows the majority of functional cells to continue providing storage capacity, while only the affected segments are marked as defective or retired, thus minimizing the impact on overall storage capacity while ensuring data integrity.
Data Source
AI summary
Weak erase detection and mitigation techniques are provided that detect permanent failures in solid-state storage devices. One exemplary method comprises obtaining an erase fail bits metric for a solid-state storage device; and detecting a permanent failure in at least a portion of the solid-state storage device causing weak erase failure mode by comparing the erase fail bit metric to a predefined fail bits threshold. In at least one embodiment, the method also comprises mitigating for the permanent failure causing the weak erase failure mode for one or more cells of the solid-state storage device. The mitigating for the permanent failure comprises, for example, changing a status of the one or more cells to a defective state and/or a retired state. The detection of the permanent failure causing the weak erase failure mode comprises, for example, detecting the weak erase failure mode without an erase failure.