Storage Controller Cache Integrity via Age Fields
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Solution Overview
Problem
Current systems with redundant storage controllers face challenges in maintaining cache data integrity and availability, especially in active-passive configurations during cascaded failures, leading to extended data unavailability and the need for manual intervention.
Innovation Solution
The implementation of age fields in metadata associated with logical volumes to indicate the validity of cache data, allowing controllers to automatically manage cache data integrity and availability by updating age values during failover and failback operations, reducing the need for manual recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If redundant storage controllers are used in active-passive configuration, then system reliability is improved, but cache data integrity cannot be guaranteed during cascaded failures
Solution Approach 1:
The system performs preliminary actions by maintaining age fields that track the recency of cache data before failures occur. During normal operation, the age fields are continuously updated to reflect the current state of cache data, so that when a failure occurs, the controller can immediately determine cache validity without needing to communicate with the failed controller. This preliminary tracking of cache age resolves the contradiction by preserving cache data integrity information in advance.
2Productivity
If cache data is maintained in redundant controllers, then data availability is improved, but the need for manual intervention increases during failures
Solution Approach 1:
The system enables self-service by equipping each controller with age fields that independently track cache data validity. When a controller experiences a failure or restart, it can autonomously determine whether its cache data is valid by checking its own age fields against the expected age values, without requiring manual intervention or communication with the other controller. This automatic determination resolves the contradiction by maintaining data availability while eliminating the need for manual recovery operations.
3Reliability
If controllers communicate to determine cache validity, then cache integrity is ensured, but system uptime is reduced during failures
Solution Approach 1:
The system extracts the cache validity determination logic from inter-controller communication and embeds it directly in each controller's local metadata structures. By taking out the need for communication and embedding age tracking fields locally, each controller can independently and immediately determine cache validity without waiting for responses from other controllers. This extraction resolves the contradiction by ensuring cache integrity through local information while minimizing system downtime.
Data Source
AI summary
A system includes first and second redundant controllers, and at least one logical volume accessible to the first and second redundant controllers. The system also includes metadata fields associated with the at least one logical volume. The metadata fields include a first age field configured to store a first age value associated with the first controller and a second age field configured to store a second age value associated with the second controller. The first age value and the second age value are employed to provide an indication of whether cache data for the at least one logical volume is valid. The system further includes a processor configured to update the first and second age values in the respective first and second age fields.