SAS Expander Connection Management via Arbitration Wait Time
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Solution Overview
Problem
Current SAS topologies lack effective connection management methodologies, particularly in prioritizing and arbitrating multiple OPEN requests in complex SAS networks, leading to inefficiencies and performance issues due to the lack of specific implementation guidelines in existing standards.
Innovation Solution
The implementation of an Expander Connection Manager/Router (ECMR) architecture that includes a broadcast primitive processor, an expander connection router, and an expander connection manager to prioritize and arbitrate OPEN requests based on Arbitration Wait Time, SAS Address, and Connection Rate, using direct, table, and subtractive routing methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple OPEN requests are handled sequentially in SAS expanders, then connection management is simplified, but request processing time and network latency increase
Solution Approach 1:
The expander is divided into multiple independent arbitration units, each handling requests for different destination ports simultaneously. This segmentation allows parallel processing of multiple OPEN requests without increasing overall system complexity, as each unit operates independently with the same simple arbitration logic.
Solution Approach 2:
The patent introduces a new dimension of parallelism by implementing multiple arbitration units that process requests simultaneously across different spatial dimensions (different destination ports). This transforms the sequential one-dimensional processing into a parallel multi-dimensional approach, reducing total processing time while maintaining simple per-unit logic.
2Ease of manufacture
If arbitration priority is based solely on arrival time, then implementation is simple, but fairness and performance deteriorate
Solution Approach 1:
The arbitration priority parameters are dynamically adjusted based on connection status and wait time. The system changes parameters such as priority level and timeout values according to real-time conditions, allowing simple implementation mechanisms to achieve fair and reliable arbitration by adapting to varying network states.
Solution Approach 2:
The arbitration mechanism incorporates feedback loops that monitor connection status and adjust priority decisions accordingly. When a connection is established or a timeout occurs, the system feeds this information back into the arbitration process, ensuring fairness and reliability while maintaining implementation simplicity through automated adjustments.
3Reliability
If SAS expanders use dedicated arbitration logic for each port pair, then connection reliability improves, but hardware cost and complexity increase
Solution Approach 1:
A single universal arbitration unit is designed to handle arbitration for any source-destination port pair by configuring its internal resources dynamically. This multi-functional approach provides reliable connection establishment for all port pairs while avoiding the need for separate dedicated arbitration logic for each pair, thus reducing overall hardware complexity and cost.
Solution Approach 2:
The patent introduces a configurable arbitration unit that acts as an intermediary between the simple arbitration logic and the complex requirements of reliable connection management. This intermediary structure allows the system to achieve reliable connections through software-based configuration rather than hardware complexity, reducing the need for dedicated physical arbitration circuits for each port pair.
4Speed
If multiple physical links are aggregated into wide ports, then bandwidth increases, but connection management complexity and deadlock risk increase
Solution Approach 1:
The wide port connection management is segmented into independent arbitration units, each handling one source-destination path. This segmentation isolates the complexity within individual units while maintaining high bandwidth through parallel processing across multiple units, preventing deadlock propagation across the entire system.
Solution Approach 2:
The system dynamically adjusts connection management behavior based on real-time status of physical links and ports. When links are aggregated into wide ports, the arbitration logic dynamically adapts its timing and priority decisions to prevent deadlocks, maintaining high bandwidth performance while managing the increased complexity through adaptive rather than static control.
Data Source
AI summary
A method and apparatus are provided for implementing connection management in SAS expander devices. SAS expanders are commonly used within a SAS network topology to allow multiple disk drives to connect to multiple host devices. The method and apparatus provides arbitration of connection requests to be setup or removed among multiple end devices and expander devices so as to increase system performance and reduce hardware cost in a standard compliant manner.