Dual Controller Snapshot Ownership for Asynchronous Replication
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Solution Overview
Problem
In dual controller storage systems, the design where ownership of snapshots is assigned to only one controller at a time is inefficient for handling IO loads targeted to read-only snapshots, leading to wasted resources and non-utilization of parallel processing power, especially in asynchronous replication where only the master controller processes data replication to remote storage systems.
Innovation Solution
Assigning a peer controller as a secondary owner of the read-only snapshot, allowing both controllers to process IO requests and replicate data simultaneously, with metadata synchronization and control messages to manage ownership and replication efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If ownership of read-only snapshot is assigned to only one controller at a time, then controller responsibility and simplicity are improved, but resource utilization and replication performance deteriorate
Solution Approach 1:
The patent segments the ownership responsibility by introducing two distinct roles: primary owner (master controller) and secondary owner (peer controller). This segmentation allows both controllers to participate in replication operations simultaneously, with the primary owner initiating replication and the secondary owner assisting in data transfer, thereby improving resource utilization without complicating the overall ownership management structure
Solution Approach 2:
The patent adds a temporal dimension to controller ownership by implementing phased ownership transfer based on metadata synchronization status. The system transitions from a static single-owner model to a dynamic multi-phase model where ownership shifts from primary to secondary controller after metadata synchronization, enabling continuous replication operations across different time phases
2Reliability
If only the master controller processes data replication, then ownership clarity is improved, but resource utilization and replication speed deteriorate
Solution Approach 1:
The patent merges the replication processing capabilities of both master and peer controllers by allowing the secondary owner to assist in data transfer operations. This combination leverages the parallel processing power of both controllers, doubling the potential bandwidth for replication operations while maintaining clear role differentiation through the primary-secondary ownership model
Solution Approach 2:
The patent ensures continuous replication operations by implementing automatic ownership transfer mechanisms. When the primary controller completes metadata synchronization, ownership transfers to the secondary controller, which then continues the replication process. This continuity eliminates idle periods and ensures that replication operations never stall, maintaining constant useful action throughout the process
Data Source
AI summary
A method, computer program product, and computer system for receiving, by a master controller, a request to create a read-only snapshot for an asynchronous source volume, wherein the master controller may be assigned ownership of the read-only snapshot. A peer controller may be assigned as a secondary owner of the read-only snapshot. Ownership of the peer controller as the secondary owner of the read-only snapshot may be revoked based upon a change in metadata of the read-only snapshot. The read-only snapshot may be replicated, asynchronously, from a replication source to a replication destination.