Metro Replication Path Selection for Single-Site Read I/O
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Solution Overview
Problem
In equidistant uniform metro replication configurations, caching the same metadata pages on both sites results in inefficient cache utilization and performance overhead due to thrashing, especially when scaling systems for practical usage scenarios with many stretched and non-stretched volumes.
Innovation Solution
Implement a methodology to select a single optimal site for receiving and servicing read I/Os directed to a stretched volume, adjusting path states to ensure fairness in resource utilization and balancing node resources, thereby optimizing I/O processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If read I/Os are serviced by both sites in an equidistant uniform metro replication configuration, then cache redundancy is provided, but cache utilization efficiency deteriorates due to thrashing
Solution Approach 1:
The patent segments the read I/O workload by directing read requests to only one site (the owner site) rather than allowing both sites to service reads. This is achieved through path state management where the host is directed to send read I/Os exclusively to the owner site, eliminating cache thrashing while maintaining cache redundancy for fault tolerance
Solution Approach 2:
The patent introduces asymmetry in the previously symmetric equidistant uniform configuration by designating one site as the owner site that services all read I/Os, while the other site becomes a non-owner site that does not service reads. This asymmetric role assignment resolves the cache thrashing problem while maintaining the benefits of synchronous replication
2Reliability
If both sites service read I/Os, then availability is improved, but system performance deteriorates due to resource imbalance and thrashing
Solution Approach 1:
The patent segments read I/O servicing responsibilities by assigning the owner site as the sole handler for read requests. This segmentation eliminates the performance degradation caused by both sites competing to service reads, while write I/Os continue to be replicated to both sites maintaining availability
Solution Approach 2:
The patent applies local quality by allowing each site to have different roles (owner vs. non-owner) with respect to read I/O servicing. The owner site has the quality of servicing reads while the non-owner site does not, optimizing resource utilization at each location based on its role in the replication configuration
3Device complexity
If path states are not managed, then configuration simplicity is maintained, but resource utilization fairness deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-establishing path states (preferred, non-preferred, or equal) before I/O operations begin. This preliminary configuration enables the system to direct read I/Os to the owner site and write I/Os to both sites, ensuring fair resource utilization without requiring complex runtime negotiations or dynamic path selection
Data Source
AI summary
In at least one embodiment, a method can include: establishing a bi-directional synchronous replication configuration for a stretched resource configured across first and second sites; determining a first difference between a first maximum normalized total I/O workload of the first site and a first current normalized total I/O workload of the first site without including read I/O workload of the stretched resource; determining a second difference between a second maximum normalized total I/O workload of the second site and a second current normalized total I/O workload of the second site without including read I/O workload of the stretched resource; and selecting, in accordance with the first difference and the second difference, only one of the first site and the second site to receive and service subsequent read and write I/Os directed to the stretched resource. The configuration can be equidistant with respect to a host and the stretched resource.