SAS Expander Isolation via Targeted Discovery
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Solution Overview
Problem
SAS expanders in data storage systems have limited ability to adapt to changes in the SAS domain, leading to inefficient resource consumption and bandwidth usage when detecting changes, as they require a complete rediscovery of the topology even for minor changes, which can be resource-intensive and wasteful.
Innovation Solution
A method is introduced to isolate bad expanders in a SAS domain using out-of-band signaling and SCSI Enclosure Services (SES) messages, allowing for the identification and isolation of problematic expanders without requiring their cooperation, thereby enabling normal operation of the SAS domain by disabling and re-enabling expanders in a controlled manner.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a complete SAS Discovery process is performed to detect any change in a SAS domain, then topology information can be accurately updated, but valuable resources in the SAS initiator and bandwidth in the SAS domain communication paths are consumed
Solution Approach 1:
The patent segments the topology discovery process into targeted queries about specific changed components rather than performing a complete domain-wide discovery. When a component is added, removed, or replaced, the system sends specific inquiry messages only to affected expanders and initiators, obtaining only the necessary topology information related to the change, thus avoiding the resource consumption of a full discovery process while maintaining accurate topology updates
Solution Approach 2:
The system performs preliminary monitoring of component status changes in the SAS domain. Before a complete discovery is needed, the system detects changes through component status messages and prepares targeted queries in advance, allowing for efficient incremental topology updates rather than periodic full discoveries
2Adaptability or versatility
If a SAS expander senses a change in the SAS domain and broadcasts a BROADCAST(CHANGE) primitive, then all SAS initiators are notified of the change, but the initiators must perform a complete SAS Discovery process which consumes valuable resources and bandwidth
Solution Approach 1:
Instead of triggering a complete discovery process across the entire SAS domain, the patent segments the response to changes by sending targeted inquiry messages only to the specific initiators and expanders affected by the detected change. This selective approach maintains adaptability to domain changes while avoiding the bandwidth waste of full-domain discovery broadcasts
Solution Approach 2:
The system performs partial discovery actions only where necessary - sending specific topology inquiry messages only to affected components rather than initiating a complete discovery process across all initiators. This partial action approach provides sufficient topology information for the change at hand without the excessive resource consumption of complete domain-wide discovery
3Reliability
If SAS expanders are isolated that are causing problems preventing normal operation of a SAS domain, then normal operation can be restored, but the isolation process requires identifying the problematic expander without knowing the specifics of the problem in advance
Solution Approach 1:
The patent extracts or removes the problematic expander from the SAS domain by isolating it through targeted disabling. The system identifies expanders that may be causing topology problems and selectively disables them to restore normal operation, effectively taking out the harmful element without requiring complete system shutdown or complex diagnostic procedures
Solution Approach 2:
The system performs self-diagnosis and self-isolation of problematic expanders by monitoring topology changes and automatically identifying expanders that cause operational issues. The SAS domain management system autonomously detects when an expander is causing problems and initiates the isolation process without external intervention, reducing the complexity of manual troubleshooting
Data Source
AI summary
A method is used in handling SAS topology problems. It is detected that a chain of SAS expanders has a bad expander that prevents communicating normal SAS data streams along the chain. Expanders are disabled in the chain, and are enabled in turn while updating a flag indicating the most recently enabled good expander, until the chain fails. Expanders are disabled in the chain, and are enabled in turn but the enabling stops after enabling the expander indicated by the flag.