Enhancements Spur Evolution of Fibre Channel SANs Page 3


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SAN Routing

Another sign of the maturation of the Fibre Channel SAN market is the increasing requirement of customers to scale their SANs to much higher port counts. The initial phase of Fibre Channel deployment was characterized by relatively small, 10-30 node SAN islands. Now, however, customers are attempting to connect multiple SAN islands into an integrated storage network, or are combining director-based SANs with departmental SANs.

This has revealed both interoperability and stability issues that threaten to limit the size of enterprise Fibre Channel SANs. Interoperability between Fibre Channel fabrics is problematic, since different switches may have various, incompatible microcode levels or may be configured in proprietary modes. The stability of large SANs is problematic due to the flat nature of Fibre Channel fabrics. By design, Fibre Channel is a link layer network, analogous to bridged LANs. While this architecture enhances performance, it also makes it vulnerable to fabric-wide disruption in the event even a single switch fails.

SAN routing is a new Fibre Channel technology initially developed by Nishan Systems to solve both switch interoperability issues and potential stability issues. It does this by providing fault isolation in multi-vendor fabric environments. Instead of building a flat, link layer network out of multiple fabric switches, SAN routing preserves the autonomy of each local SAN island while providing connectivity for authorized devices between SANs.

Since faults are not allowed to propagate between SANs, stability is achieved. And because fabrics are not connected directly together, interoperability issues are overcome. In effect, SAN routing gives Fibre Channel the ability to scale to enterprise-wide configurations that are not practically feasible with native Fibre Channel switch-to-switch connections.


Collectively, these new options for Fibre Channel SANs extend the usefulness of the technology, both in terms of supporting an increased variety of storage applications and in making the technology available to a broader market. This in turn provides more flexibility for customers to select the technologies that best satisfy their storage requirements while avoiding the prospect of forklift upgrades in transitioning from one technology to another.

Tom Clark
Director of Technical Marketing, Nishan Systems
Author: Designing Storage Area Networks Second Edition (2003) (available at Amazon.com), IP SANs (2002) (also available at Amazon.com).

» See All Articles by Columnist Tom Clark

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