Non-disruptive Storage Upgrade via Co-existing Write Logs
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Solution Overview
Problem
The existing ring-based write log architecture in data storage systems faces challenges with large stepwise resource freeing due to the 'tail movement constraint', leading to inefficient space reclaiming and making upgrades disruptive, as they require stopping the system to convert persistent structures.
Innovation Solution
A non-disruptive upgrade method is introduced, where a pool-based write log is created and mirrored with the ring-based log, allowing concurrent operation and eventual exclusive use of the pool-based log, enabling smoother space reclaiming and resource recycling without system disruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a ring-based write log is used, then write operation latency is optimized, but space reclaiming efficiency deteriorates due to tail movement constraint
Solution Approach 1:
The patent transitions from a static ring-based log structure with fixed tail movement to a dynamic pool-based log structure where entries can be freed from any position. The pool-based log dynamically allocates and frees log entries based on actual usage patterns, allowing efficient space reclamation without the constraints of sequential tail movement, thus resolving the contradiction between write latency optimization and space reclaiming efficiency
Solution Approach 2:
The patent changes the fundamental parameter of log entry management from sequential (ring-based) to random access (pool-based). By changing how log entries are organized and accessed, the system maintains the low-latency write performance of ring-based logs while enabling efficient space reclamation through random access capabilities of pool-based logs, allowing entries to be freed immediately after being processed
2Reliability
If the system is stopped to convert persistent structures during upgrade, then upgrade completeness is ensured, but system availability deteriorates
Solution Approach 1:
The patent applies preliminary action by creating the pool-based log structure in advance while the system is still running. The new pool-based log is pre-initialized and prepared before the upgrade is complete, allowing the system to switch to the new structure without interruption. This eliminates the need to stop the system during conversion, maintaining availability while ensuring upgrade completeness
Solution Approach 2:
The patent introduces an intermediary mechanism during the upgrade transition. The update flag acts as an intermediary state that coordinates the transition from ring-based to pool-based log. This intermediary allows the system to maintain operational continuity while the conversion happens in the background, ensuring both upgrade completeness and system availability
3Productivity
If a pool-based write log is created and mirrored concurrently with ring-based log, then space reclaiming efficiency is improved, but device complexity increases
Solution Approach 1:
The patent uses copying by creating a pool-based log that mirrors the ring-based log structure during the transition period. The pool-based log is initialized as a copy of the existing ring-based log, allowing the system to maintain both structures temporarily. This copying approach enables efficient space reclamation in the new structure while keeping the transition process manageable by reusing the existing log data
Solution Approach 2:
The patent maintains continuity of useful action by having both log structures coexist and operate simultaneously during the transition. The mirroring process continues in the background while the system operates normally, and the update flag ensures seamless switching when the transition is complete. This continuous operation minimizes the impact of the increased complexity on system performance
Data Source
AI summary
A data storage system non-disruptively transitions from using a ring-based write log to using a pool-based write log for buffering data being written to persistent secondary storage. The system initially creates the pool-based write log based on contents of the ring-based write log, and begins to mirror updates of the ring-based write log to the pool-based write log to establish synchronism. Subsequently, and based on an update flag indicating that an update process for the system has not yet completed, the system continues to mirror updates of the ring-based write log to the pool-based write log to maintain synchronism therebetween. Subsequently, and based on the update flag indicating that the update process for the system has completed, the system commences exclusive use of the pool-based write log and making the ring-based write log available for eventual removal.