Smart Discovery in SAS Expanders for I/O Stall Reduction
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Solution Overview
Problem
In large SAS topologies, device discovery processes generate significant traffic and stall I/O operations when a device goes missing, leading to prolonged discovery times and reduced performance due to the need for all initiators to re-establish connections.
Innovation Solution
Implementing a 'smart' discovery process that allows expanders to initiate and manage device updates independently, reducing traffic and enabling initiators to maintain I/O operations with other devices, using vendor unique SMP frames to broadcast and update topology changes in real-time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all SAS devices perform discovery when a device goes missing, then topology accuracy is maintained, but data traffic increases significantly and I/O operations are blocked
Solution Approach 1:
The patent segments the discovery process by identifying and isolating the affected path from the initiator to the missing device. Only expanders and devices along this specific path perform discovery, rather than all devices in the topology. This segmentation reduces the number of devices involved in discovery from potentially tens of devices to only those necessary for maintaining accurate topology information.
Solution Approach 2:
The patent applies local quality by making the discovery behavior dependent on the device's position in the topology. Devices on the affected path perform discovery, while devices not on this path do not. This localized approach ensures topology accuracy is maintained where needed while avoiding unnecessary discovery traffic in other parts of the system.
2Loss of information
If discovery is performed to update topology information, then device presence accuracy is improved, but I/O operations to other devices are stalled
Solution Approach 1:
The patent segments the impact of discovery by limiting it to only those devices and paths affected by the missing device. This ensures that I/O operations to devices not on the affected path continue without interruption, while still maintaining accurate topology information for the affected portion of the system.
Solution Approach 2:
The patent performs partial discovery action by having only the necessary devices on the affected path perform discovery, rather than requiring complete topology-wide discovery. This partial action is sufficient to maintain device presence accuracy for affected operations while minimizing the blocking of I/O operations.
3Reliability
If direct connections are made between initiator and each target device, then data transfer reliability is improved, but device complexity and connection management increase
Solution Approach 1:
The patent uses expanders as intermediaries to manage connections between initiators and target devices. The expander on the affected path performs discovery and maintains topology information, allowing the initiator to access multiple target devices through the expander without requiring direct management of each connection. This intermediary approach maintains reliable data transfer while reducing initiator complexity.
Data Source
AI summary
Methods, systems and processor-readable media are disclosed for implementing a “smart” discovery process in a data transfer regime having one or more expanders and one or more initiators. Data traffic associated with such a discovery process can be reduced and one or more of the initiators can be prevented from blocking input/output to particular components in communication with the data transfer regime, thereby improving and completing the discovery process in an optimal time frame while enhancing the performance of the initiator(s).