Hybrid HDD Data Retention Error Detection
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Solution Overview
Problem
NAND-based memory cells in hybrid hard disk drives and solid-state drives face data retention challenges due to charge leakage, which is accelerated by high temperatures and radiation, leading to uncertain data retention times and reduced reliability compared to other storage media.
Innovation Solution
Implementing a system where test data is written and read in nonvolatile solid-state devices to detect data retention errors, using modified write and read processes to increase sensitivity to incipient charge leakage, and rewriting user data to maintain data integrity by relocating it when quality thresholds are met.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If NAND-based memory cells are used in hybrid HDDs, then data access speed is improved, but data retention reliability deteriorates due to charge leakage
Solution Approach 1:
The system performs preliminary actions by writing test data to memory blocks before storing user data, then periodically reading and evaluating the test data to detect charge leakage early. When degradation is detected, user data is proactively rewritten to new blocks before actual data loss occurs, thus maintaining reliability while preserving the speed benefits of NAND memory
Solution Approach 2:
Test data serves as an intermediary indicator to monitor the health of memory blocks. By evaluating test data quality rather than directly monitoring physical charge levels, the system can indirectly detect degradation trends and trigger preventive rewriting operations, resolving the contradiction between maintaining fast access and ensuring data reliability
2Reliability
If test data is continuously monitored and user data is proactively rewritten, then data retention reliability is improved, but device complexity increases
Solution Approach 1:
The memory device is segmented into multiple blocks, with each block containing both user data and associated test data. This segmentation allows independent monitoring and rewriting of individual blocks without affecting the entire memory device, managing complexity through modular organization while maintaining high reliability through targeted preventive actions
3Reliability
If data is frequently rewritten to maintain quality, then data retention reliability is improved, but loss of time increases due to rewriting operations
Solution Approach 1:
The system implements feedback control by periodically reading test data, evaluating its quality against thresholds, and only triggering rewriting operations when degradation exceeds acceptable levels. This feedback mechanism optimizes the balance between maintaining reliability and minimizing unnecessary rewriting operations that would consume time and reduce overall system performance
Data Source
AI summary
Data are refreshed in a nonvolatile solid-state device to significantly reduce the likelihood of data retention errors. Test data are written in a region of the nonvolatile solid-state device when user data are stored in the nonvolatile solid-state device, and are subsequently read to detect the possibility of data retention errors occurring when the associated user data are read. The test data may be a portion of the user data or a predetermined test pattern. To increase sensitivity to incipient charge leakage that may compromise the user data, the test data may be written using a modified write process and/or read with a modified read operation. The nonvolatile solid-state device may be employed as part of a solid-state drive or as the flash-memory portion of a hybrid hard disk drive.