Block Mapping Recovery via Generation Numbers
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Solution Overview
Problem
Current block storage systems face inefficiencies in recovering the mapping between virtual and physical blocks, requiring a full scan of physical blocks to reconstruct the block mapping structure, which impacts system availability.
Innovation Solution
A method and system that utilize a block mapping structure with a descriptor table and a block validity tracking structure, employing generation numbers and alternating updates to maintain and recover the mapping without scanning the entire block set, ensuring fast recovery by tracking changes and maintaining redundant data structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a full scan of physical blocks is performed to reconstruct the block mapping structure, then the mapping data can be recovered, but the system availability deteriorates due to the time-consuming recovery process
Solution Approach 1:
The patent maintains a block mapping structure that is preliminarily updated whenever block mappings change. This structure includes descriptor tables and validity tracking information that are kept current through alternating updates (first copy/second copy mechanism). When recovery is needed, the pre-maintained block mapping structure can be immediately used without requiring a full scan, thus resolving the contradiction between reliable recovery and quick recovery time.
2Speed
If redundant tracking of mapping data is maintained to enable fast recovery, then the recovery speed improves, but the device complexity increases due to additional data structures and update mechanisms
Solution Approach 1:
The block mapping structure is segmented into multiple descriptor tables (first descriptor table, second descriptor table) and validity tracking structures. Each segment has a specific function: some track mappings, others track validity states. This segmentation allows the system to maintain redundant information in an organized manner, enabling fast recovery while managing complexity through modular design. The alternating update mechanism between segments further simplifies the recovery process.
Solution Approach 2:
The patent creates and maintains copies of the block mapping structure (first copy, second copy) that are updated alternately. These copies serve as redundant tracking mechanisms that enable fast recovery. By copying and alternately updating the mapping data, the system achieves fast recovery speed while the copying mechanism itself provides a structured approach to managing the complexity of redundant data maintenance.
Data Source
AI summary
A computer-implemented method and apparatus manages block mapping. The block mapping maps physical blocks in a block storage device to virtual blocks of a virtual address space. The method involves assigning a generation number from a net of generation numbers to each block mapping entry, where the block mapping entry correlates a physical block with a virtual block. A maximum generation number of the set of generation numbers is increased and a first block mapping entry is marked dirty in response to an update of a correlated first virtual block. A generation number of the first block mapping entry is set to the maximum generation number. Finally, a generation number of a second block mapping entry having a lowest generation number is set to a generation number of the first block mapping entry.