SAS Expander Arbitration Suspension for Initiator Failure
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Solution Overview
Problem
In SAS domains, initiator failures lead to increased arbitration wait times and operational disruptions due to target devices attempting to connect to non-functional initiators, causing race conditions and clogging of discovery processes.
Innovation Solution
Implementing a system where SAS expanders detect initiator failures, suspend arbitration, and direct target devices to wait for alternative connections, allowing for discovery process updates and preventing subsequent connections to non-functional initiators by denying connections based on increased arbitration wait times and performing discovery to update routing tables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If target devices continue to attempt connections to initiators during discovery process, then connection arbitration can proceed, but arbitration wait times increase dramatically and operations are crippled
Solution Approach 1:
The expander performs preliminary actions by detecting initiator failures and suspending arbitration before target devices can continue attempting connections. This prevents the accumulation of wasted arbitration wait times by proactively identifying failed initiators and stopping arbitration processes directed toward them, thereby maintaining overall domain productivity.
2Reliability
If target devices attempt to connect to failed initiators, then arbitration processes can continue, but race conditions occur and discovery processes are clogged
Solution Approach 1:
The expander implements feedback mechanisms by monitoring initiator status and using this information to control arbitration processes. When an initiator failure is detected, the expander provides feedback to suspend arbitration, preventing target devices from attempting connections to failed initiators and thereby eliminating the race conditions that would otherwise occur.
3Object-generated harmful factors
If arbitration is suspended when initiator failure is detected, then race conditions are prevented, but additional detection and control mechanisms are required
Solution Approach 1:
The expander serves as an intermediary between initiators and target devices, mediating the connection arbitration process. It detects initiator failures and controls arbitration suspension, acting as a mediator that prevents race conditions without requiring complex changes to target devices or initiators themselves. This centralized mediation approach manages complexity within the expander rather than distributing it across multiple components.
Data Source
AI summary
Systems and methods presented herein provide for managing connections in a SAS domain comprising at least first and second expanders. The first expander detects a failure of the initiator and indicates a change in the SAS domain to the second expander. The second expander detects an increase in arbitration wait time for a connection between the initiator and the target device, determines a race condition exists in the second expander, denies the connection between the initiator and the target device, directs the target device to wait for another connection, performs a discovery of the domain based on the discovery request from the first expander, and prevents a subsequent connection by the target device to the initiator after discovery completes.