Partial Garbage Collection for SSD Error Handling
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Solution Overview
Problem
Conventional garbage collection methods in data storage devices like solid-state drives (SSDs) operate on large block management regions, leading to inefficient memory erasure and prolonged recovery times due to the need to manage extensive data ranges, which is not suitable for localized error handling and can cause congestion in operations like TRIM commands.
Innovation Solution
Implementing partial garbage collection by minimizing the memory region size to that of a single flash page or system journal, allowing for localized and piecemeal garbage collection, and interleaving data band and invisible band journal processing to prevent thrashing and congestion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional garbage collection operates on large block management regions, then comprehensive memory management is achieved, but recovery time increases and operational congestion occurs
Solution Approach 1:
The patent divides the memory management system into two distinct segments: a data band for user data and an invisible band for system metadata and journals. This segmentation allows garbage collection to operate independently on small regions within the invisible band rather than processing entire large block management regions, significantly reducing recovery time while maintaining complete memory management through coordinated operations in both bands.
2Reliability
If garbage collection processes large block management regions, then thorough data recovery is ensured, but operational congestion and thrashing occur
Solution Approach 1:
By segmenting memory into data band and invisible band, the patent enables parallel and independent garbage collection operations in the invisible band that do not interfere with data band operations. This eliminates thrashing and operational congestion while ensuring thorough data recovery through systematic processing of system metadata and journals in the invisible band.
Solution Approach 2:
The invisible band acts as an intermediary layer between the host and the data band, handling system metadata, journals, and garbage collection operations. This intermediary structure allows garbage collection to process small managed regions in the invisible band without blocking data operations in the data band, maintaining high operational throughput while ensuring complete data recovery.
3Loss of time
If garbage collection operates on minimal memory regions, then recovery speed increases, but comprehensive memory management becomes difficult
Solution Approach 1:
The patent resolves this contradiction by segmenting memory management responsibilities: the invisible band handles system metadata and journals with fast garbage collection on small regions, while the data band manages user data. This segmentation enables rapid recovery in the invisible band while comprehensive memory management is achieved through the coordinated two-band architecture.
Solution Approach 2:
The invisible band serves as an intermediary that manages system metadata and journals independently, allowing fast garbage collection on minimal regions without compromising comprehensive memory management. The intermediary invisible band coordinates with the data band to ensure complete memory management while enabling rapid recovery operations.
Data Source
AI summary
A method for managing garbage collection of memory locations in an DSD having a plurality of dies each having a plurality of memory blocks includes: selecting a physical region of memory to be garbage collected, the selected physical region being a subset of a block management region; and garbage collecting the selected physical region. The garbage collecting includes: determining one or more journals corresponding to the selected physical region, the journal comprising transaction entries indicating what logical data are written to memory locations in the selected physical region; determining whether the memory locations within the physical region contain valid data based on a comparison of information in the journal and a mapping table; and if valid data exists, copying valid data into memory locations in memory regions other than the selected physical region of memory. The selected physical region of memory is erased when the block management region is erased.