NAND Flash Block Grouping for Dynamic Refresh Management
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Solution Overview
Problem
Flash memory-based storage devices face performance degradation and stability issues due to frequent refresh operations needed to counteract characteristic degradation in NAND blocks, leading to increased overhead and difficulty in processing user requests.
Innovation Solution
A storage device with processing circuitry that monitors characteristic degradation rates, groups blocks based on these rates, and determines tailored refresh periods for each group to efficiently manage refresh operations, thereby dispersing overhead and maintaining stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If refresh operations are performed frequently on all blocks to counteract characteristic degradation, then retention characteristics are improved, but device performance and stability deteriorate due to increased overhead
Solution Approach 1:
The patent segments the cell array into multiple groups based on characteristic degradation rates. Each group is refreshed independently according to its specific refresh period, rather than refreshing all blocks uniformly. This segmentation allows the system to maintain reliability for blocks needing frequent refresh while reducing overhead for blocks with lower degradation rates.
Solution Approach 2:
The patent implements dynamic refresh period determination for each group based on monitored characteristic degradation rates. The refresh periods are not fixed but are adjusted according to the actual degradation characteristics of each group, allowing the system to adaptively optimize between reliability and performance as conditions change.
2Reliability
If refresh operations are performed simultaneously on multiple blocks, then characteristic degradation is addressed efficiently, but device stability worsens due to performance deviation and difficulty in processing user requests
Solution Approach 1:
By dividing blocks into multiple groups with different refresh periods, the patent prevents simultaneous refresh operations across all blocks. Groups are refreshed at different times according to their specific periods, which distributes the refresh load and maintains device stability while still addressing characteristic degradation effectively.
Data Source
AI summary
A storage device may include a monitoring module which monitors a characteristic degradation rate of a plurality of blocks included in a cell array of a nonvolatile memory; a group management module which designates the plurality of blocks as one or more groups, on the basis of a monitoring result of the monitoring module; a refresh period management module which determines refresh periods for each of the one or more groups; and a processor which performs refresh on the one or more groups in accordance with the determined refresh periods.