Mirrored Storage Cache Flush for Power-Loss Data Synchronization
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Solution Overview
Problem
In mirrored storage arrays, maintaining data synchronization between logical units is challenging due to the use of volatile write caches, which can lead to data loss during power events, compromising data integrity and requiring traditional approaches to sacrifice speed and performance.
Innovation Solution
A method and system that maintain a pointer and flag to track data synchronization, detecting power events and attempting to flush the write cache to non-volatile storage, ensuring accurate synchronization by setting a flag upon successful flush, allowing for continued synchronization from the correct point upon re-powering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If write cache is used to increase data access speed, then productivity is improved, but reliability deteriorates due to data loss during power events
Solution Approach 1:
The system performs preliminary actions by detecting power events before data loss occurs and flushing the write cache to non-volatile storage in advance. The controller monitors for power events and executes a flush operation to transfer dirty data from volatile write cache to non-volatile storage before the power event causes data loss, thereby maintaining both high productivity and reliability.
Solution Approach 2:
The system implements feedback mechanisms by tracking the synchronization status between primary and mirror logical units using pointers and status flags. The controller continuously monitors whether data in the write cache has been successfully flushed to non-volatile storage and adjusts its operation accordingly, enabling it to distinguish between writes to cache and writes to permanent storage, thus resolving the reliability issue while maintaining performance.
2Reliability
If traditional approaches are used to ensure data integrity, then reliability is improved, but productivity deteriorates due to sacrificed speed and performance
Solution Approach 1:
The system dynamically adjusts its operation based on the presence and status of write cache. When write cache is detected, the system operates in high-performance mode allowing volatile caching, while continuously monitoring for power events and tracking synchronization status. The controller dynamically switches between performance-optimized and safety-optimized modes, enabling it to maintain high productivity when conditions permit while ensuring reliability when needed.
3Reliability
If write cache flushing is performed on every power event, then reliability is improved, but productivity deteriorates due to increased time for cache flush operations
Solution Approach 1:
The system implements self-service by autonomously detecting power events and automatically flushing the write cache without requiring host intervention or system shutdown. The controller monitors its own operational state, detects power events, and executes flush operations independently, minimizing the impact on productivity while ensuring reliability through automatic cache management.
Solution Approach 2:
The system performs cache flush operations as a preliminary action immediately upon detecting a power event, before the system shuts down or enters standby mode. By executing the flush operation proactively at the moment of power event detection, the system minimizes data loss risk while reducing the overall time penalty compared to traditional approaches that require complete system shutdowns or extended verification periods.
Data Source
AI summary
Systems and methods for synchronizing redundant data in a storage array are disclosed. In accordance with a method, a pointer indicating the amount of data synchronized between a first storage resource to a second storage resource may be maintained and a power event may be detected. In response to the detection of the power event, an attempt may be made to flush a write cache associated with the second storage resource to transfer data from the write cache to a non-volatile storage area of the second storage resource. A determination may be made whether the attempt to flush the write cache is successful. In response to determining that the attempt to flush the write cache is successful, a flag may be set to indicate that the pointer accurately indicates the amount of data mirrored from the first storage resource to the non-volatile storage area of the second storage resource.