Leased Lock Mechanism for Active-Active DAS Performance
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Solution Overview
Problem
In Active-Active High Availability Direct Attached Storage (DAS) RAID systems, conventional locking mechanisms become a major overhead due to the need for coordination and inter-controller communication for Input/Output (IO) requests to the same set of virtual disks, which reduces system performance.
Innovation Solution
Designating one server as an owner server for overall lock control, allowing peer servers to take a long-term lease on frequently accessed 'hot' windows and process IOs using local locks, minimizing inter-controller communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional locking mechanisms are used for coordination between controllers, then data consistency is maintained, but system performance deteriorates due to major overhead from inter-controller communication
Solution Approach 1:
The patent segments the locking mechanism into two parts: (1) an owner server that maintains centralized lock state for metadata and coordination, and (2) peer servers that use local locks for IO processing. This segmentation allows peer servers to process IO requests independently without continuous inter-controller communication, while the owner server ensures data consistency through lease management and metadata locking.
Solution Approach 2:
The patent implements preliminary action through lock leases where the owner server pre-allocates lock leases to peer servers for specific windows before IO operations. This allows peer servers to acquire local locks in advance and process IO requests without real-time coordination with the owner server, reducing communication overhead while maintaining consistency.
2Measurement precision
If inter-controller communication is increased for lock coordination, then locking accuracy is improved, but communication overhead increases
Solution Approach 1:
The patent applies local quality by allowing peer servers to use local locks for IO processing within their leased windows, eliminating the need for continuous inter-controller communication. The owner server maintains precise lock state for metadata and lease management, while peer servers operate independently for data plane IO operations, reducing communication overhead while maintaining locking accuracy where needed.
3Device complexity
If centralized lock control is implemented on the owner server, then lock management simplifies, but the owner server becomes a bottleneck
Solution Approach 1:
The patent segments lock management responsibilities between the owner server (metadata locking, lease allocation) and peer servers (local IO locking). This segmentation prevents the owner server from becoming a bottleneck by allowing peer servers to handle IO locking locally, while the owner server focuses on higher-level coordination tasks with reduced frequency.
Solution Approach 2:
The owner server performs preliminary actions by allocating lock leases to peer servers before IO operations begin. Once leases are granted, peer servers can process IO requests independently using local locks without continuous owner server involvement, eliminating the bottleneck while maintaining simplified centralized management for critical operations.
Data Source
AI summary
A method and system for IO processing in a storage system is disclosed. In accordance with the present disclosure, a controller may take long term “lease” of a portion (e.g., an LBA range) of a virtual disk of a RAID system and then utilize local locks for IOs directed to the leased portion. The method and system in accordance with the present disclosure eliminates inter-controller communication for the majority of IOs and improves the overall performance for a High Availability Active-Active DAS RAID system.