Fast Path I/O Circuit Handling Stale Mapping in Clustered Storage
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Solution Overview
Problem
In clustered storage systems, 'fast path' I/O requests can be hindered by outdated mapping information, leading to errors and performance issues when ownership of logical volumes is transferred between storage controllers, as host systems may continue to issue requests using stale data before updated mapping information is received.
Innovation Solution
The implementation of a fast path I/O request processing circuit within storage controllers that converts stale 'fast path' requests into logical volume requests using mapping context information, allowing these requests to be processed by the appropriate storage controller, even if the original controller is not the owner, thereby avoiding errors and ensuring seamless operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If storage controllers transfer ownership of logical volumes to balance processing load, then overall system performance is improved, but host systems may continue using stale mapping information causing I/O request errors
Solution Approach 1:
The patent introduces a fast path I/O request processing circuit as an intermediary component between the host system and the storage controller's logical volume processing stack. This circuit receives fast path I/O requests from the host, converts them into logical volume requests using current mapping information, and forwards them to the appropriate storage controller, thereby resolving the contradiction between performance optimization through ownership transfer and reliability through stale mapping information
Solution Approach 2:
The patent changes the state of I/O requests from direct fast path requests to converted logical volume requests by modifying their format and processing path. This parameter change allows the system to maintain both fast path performance and proper ownership awareness, resolving the contradiction between speed and reliability
2Speed
If storage controllers process fast path I/O requests directly, then processing speed is improved, but outdated mapping information causes errors when ownership has changed
Solution Approach 1:
The fast path I/O request processing circuit serves as an intermediary that maintains the speed advantage while introducing correctness. It receives high-speed fast path requests, converts them using current mapping information, and forwards them appropriately, thus resolving the contradiction between speed and accuracy
Solution Approach 2:
The system performs preliminary conversion of fast path requests into logical volume requests before processing, using current mapping information. This preliminary action prevents errors from outdated mapping information while maintaining the fast path processing speed
3Productivity
If host systems use stale mapping information for fast path requests, then request processing remains fast, but errors occur when storage controller ownership changes
Solution Approach 1:
The fast path I/O request processing circuit acts as a mediator that translates stale fast path requests into correct logical volume requests, eliminating errors while preserving throughput by maintaining the fast path processing architecture
4Productivity
If storage controllers implement fast path processing circuits, then processing capability is improved, but complexity increases due to additional conversion logic
Solution Approach 1:
The patent segments the I/O request processing into distinct paths: fast path requests are handled by a dedicated fast path processing circuit, while logical volume requests are handled by the logical volume processing stack. This segmentation allows the fast path circuit to be a simpler, specialized component rather than a complex universal processor
Solution Approach 2:
The fast path I/O request processing circuit is designed as a relatively simple intermediary component that performs conversion between request formats. This intermediary approach adds minimal complexity while significantly improving processing capability
Data Source
AI summary
Methods and structure for improved processing of fast path I/O requests in a clustered storage system. In a storage controller of a clustered storage system, the controller comprises a fast path I/O request processing circuit tightly coupled with host system drivers for fast processing of requests directed to storage devices of a logical volume. The controller also comprises a logical volume I/O processing stack (typically implemented as programmed instructions) for processing I/O requests from a host system directed to a logical volume. Based on detecting a change of ownership of a device or volume and/or a change to logical to physical mapping of a logical volume, fast path I/O requests may be converted to logical volume requests based on mapping context information within the fast path I/O request and shipped within the clustered storage system for processing.