Persistent WWN-FCID Assignment in Fibre Channel SANs
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Solution Overview
Problem
In Fibre Channel (FC) Storage Area Networks (SANs), the assignment of World Wide Names (WWNs) to Fibre Channel Identifiers (FCIDs) is not persistent, leading to inconsistent FCID assignments during server login attempts, especially after link or server resets, due to load balancing techniques used by Fibre Channel Forwarders (FCFs).
Innovation Solution
Implementing a messaging system with an N_Port ID Virtualization (NPIV) Proxy Gateway (NPG)/Input-Output Aggregator (IOA) engine that sets a persistent WWN-FCID bit in subsequent fabric logins, ensuring that subsequent fabric discoveries are sent through the same port used for the initial login, thereby maintaining consistent FCID assignments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If load balancing techniques are used by FCF to determine which link has the lowest load, then resource utilization is improved, but WWN-FCID assignment consistency deteriorates
Solution Approach 1:
The system performs preliminary actions by setting a persistent WWN-FCID bit in the fabric login message before the actual FCID assignment process. This preliminary action ensures that the FCF device will maintain consistency in WWN-FCID assignments by forcing subsequent fabric discoveries to use the same link as the initial login, thereby resolving the contradiction between load balancing and assignment consistency.
2Reliability
If multiple and/or redundant links are used by FCF to FC switch, then system reliability is improved, but FCID assignment persistence deteriorates
Solution Approach 1:
The invention applies local quality by making the FCF device evaluate and select specific links based on the persistent WWN-FCID bit setting for each WWN. Instead of uniformly applying load balancing across all links, the system assigns different quality characteristics to different link selection processes, ensuring that each WWN consistently uses the same link while the system maintains multiple redundant links for overall reliability.
3Productivity
If FCF performs load balancing across multiple links, then throughput is improved, but login attempt consistency deteriorates
Solution Approach 1:
The system performs preliminary action by setting the persistent WWN-FCID bit in the fabric login message, which instructs the FCF device to maintain consistent link selection for subsequent login attempts. This preliminary configuration allows the system to achieve both high throughput through multiple links and consistent login behavior by establishing the link selection criterion before login attempts occur.
Data Source
AI summary
A persistent World Wide Name (WWN)-Fiber Channel Identifier (FCID) assignment system includes a Fiber Channel (FC) networking device and a server device that sets a persistent WWN-FCID bit in a second fabric login that is directed to the FC networking device subsequent to a first fabric login that was directed to the FC networking device and that resulted in the assignment of an FCID to a WWN for the server device. An FC Forwarder (FCF) device receives the second fabric login from the server device. In response to determining that the persistent WWN-FCID bit is set in the second fabric login, the FCF device sends the FC networking device a second fabric discovery corresponding to the second fabric login through a port that was used to send the FC networking device a first fabric discovery corresponding to the first fabric login.