Two-Phase Discard Scan Process for Flashcopy Efficiency
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Solution Overview
Problem
Discard scans in computing storage environments often suffer from inefficiencies due to the need to wait for track access, leading to reduced productivity and prolonged I/O operations during flashcopy establish and withdraw operations.
Innovation Solution
Implementing a two-phase discard scan process where tracks are marked for demotion in the first phase without waiting for track access, allowing subsequent demotion by other processes, and a cleanup demotion phase for any remaining tracks in the second phase, thereby eliminating wait times and enhancing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a traditional discard scan waits for track access completion before marking tracks for demotion, then data integrity is maintained, but scan efficiency and productivity are reduced
Solution Approach 1:
The patent applies preliminary action by marking tracks for demotion immediately when discard scan identifies them as candidates, without waiting for track access operations to complete. This allows the discard scan to proceed proactively through the directory structure and mark multiple tracks in advance, eliminating idle wait time while maintaining data integrity through coordinated demotion execution
2Speed
If a discard scan marks tracks for demotion without waiting for track access, then scan speed increases, but risk of data inconsistency increases
Solution Approach 1:
The patent implements feedback mechanisms where the system continuously monitors track access status and demotion completion. When a track is marked for demotion, the system tracks its access patterns and confirms demotion execution, providing feedback loops that ensure data consistency is maintained even as scan speed increases through non-blocking operations
Solution Approach 2:
The patent introduces an intermediary demotion coordination mechanism that sits between the discard scan marking process and actual track demotion execution. This intermediary layer coordinates demotion operations, ensuring that tracks are only actually demoted when safe to do so, thereby maintaining data consistency while allowing the scan itself to proceed at high speed without direct blocking
3Productivity
If multiple tracks are processed in a single discard scan, then productivity improves, but I/O hold time during flashcopy operations increases
Solution Approach 1:
The patent applies segmentation by dividing the discard scan process into distinct phases: identification phase where candidate tracks are marked, and execution phase where demotion actually occurs. This segmentation allows the scan to quickly identify and mark multiple tracks without holding I/O operations, then execute demotions separately, thereby increasing productivity while minimizing I/O hold time
Data Source
AI summary
A plurality of tracks is examined for meeting criteria for a discard scan. In lieu of waiting for a completion of a track access operation, at least one of the plurality of tracks is marked for demotion. An additional discard scan may be subsequently performed for tracks not previously demoted. The discard and additional discard scans may proceed in two phases.