Sub-block Garbage Collection for Nonvolatile Memory Interference
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Solution Overview
Problem
As nonvolatile memory devices increase in capacity, existing memory management policies, including garbage collection operations, often mismatch with the requirements of these devices, leading to inefficiencies and errors due to word line interference during erase operations.
Innovation Solution
A storage device with a memory controller that selects a garbage collection victim sub-block based on the number of valid pages of both the sub-block and adjacent word lines, considering condition information such as program-erase cycle and degradation, to minimize interference and optimize garbage collection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If garbage collection is performed on entire blocks instead of sub-blocks, then management is simpler, but erase time increases and interference between adjacent word lines worsens
Solution Approach 1:
The memory block is divided into multiple sub-blocks that can be independently erased. The garbage collection operation selectively erases only the necessary sub-blocks rather than entire blocks, reducing erase time and minimizing interference with adjacent word lines while maintaining manageable complexity through structured organization.
2Device complexity
If garbage collection selects victim blocks without considering adjacent word lines, then selection process is simpler, but word line interference errors increase
Solution Approach 1:
The garbage collection mechanism incorporates feedback by counting valid pages in both the candidate victim sub-block and adjacent word lines. This feedback information is used to make informed selection decisions, ensuring that victim selection considers potential interference with adjacent data, thereby improving reliability without excessive complexity.
3Quantity of substance
If all sub-blocks are erased during garbage collection, then free space is maximized, but unnecessary data loss occurs and performance decreases
Solution Approach 1:
The garbage collection operation applies local quality by selectively erasing only specific sub-blocks that are identified as victims based on valid page counts and interference considerations. This localized approach creates sufficient free space for new data while preserving valuable data in other sub-blocks, improving overall efficiency.
Data Source
AI summary
A storage device is provided as follows. A nonvolatile memory device includes blocks, each block having sub-blocks erased independently. A memory controller performs a garbage collection operation on the nonvolatile memory device by selecting a garbage collection victim sub-block among the sub-blocks and erasing the selected garbage collection victim sub-block to generate a free sub-block. The memory controller selects the garbage collection victim sub-block using valid page information of each sub-block and valid page information of memory cells adjacent to each sub-block.