Enhancements Spur Evolution of Fibre Channel SANs

Tuesday Sep 9th 2003 by Tom Clark
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Enhancements Spur Evolution of Fibre Channel SANs

With over ten years of standards and product development behind it, Fibre Channel is now a mature and established technology for storage networking. Link layer protocols are efficient and stable; switches provide high performance and are scaling to higher port counts; and Fibre Channel arrays, tape subsystems, and host connections are offered by all the major storage suppliers.

Although iSCSI may eventually displace Fibre Channel connections for server attachment, Fibre Channel will not disappear overnight. If anything, iSCSI is being viewed more as a complementary solution for Fibre Channel SANs, since customers can now amortize the cost of their Fibre Channel storage investments over much larger populations of Wintel servers.

In addition, new developments in Fibre Channel offerings are enhancing the value of traditional SANs, both for enterprise networks and for the broader medium and small business market. Let's take a look at some of the most important developments on the Fibre Channel front.

Mid-Tier Solutions

To date, Fibre Channel SANs have enjoyed success primarily in large enterprise networks. The lack of market penetration of SANs to medium and small businesses has not been due to architectural issues, but rather primarily to the cost and complexity of adopting a new, relatively expensive technology. The recent introduction of SAN solutions aimed at medium and small businesses, however, is accelerating the adoption of SANs by a broader market and is bringing the benefits of SANs to more users.

Medium and small businesses, after all, face the same storage problems as their enterprise brethren. The steady accumulation of direct-attached storage inevitably results in excessive administrative overhead, complex and sometimes unworkable backup strategies, and an inability to provide high availability access to data. More affordable SAN solutions enable mid-tier companies to benefit from storage consolidation, centralized tape backup, and server clustering applications previously available only to enterprise budgets.

This technology tickle-down is being led by vendors such as Dell (through the EMC CLARiiON line) and HDS (through the 9500 modular storage arrays), which are packaging SAN solutions targeted to medium and smaller business budgets. Even high-end storage applications such as disaster recovery are coming to mid-tier customers as lower cost data replication and storage over IP products are introduced.

SAN costs for the mid-range market are also being contained by new Fibre Channel switches such as the McDATA Sphereon switches, which are based on a high port density ASIC, as well as low cost tape subsystems from vendors such as SpectraLogic. Collectively, these new mid-tier SAN solutions are expanding the installed base of Fibre Channel, even as new iSCSI products come to market.

Page 2: Speed

Speed

Early SAN products were based on quarter-speed Fibre Channel, providing 25 MBps throughput. Quarter-speed quickly gave way to full Gigabit (Gb) speed Fibre Channel, which after a few years has been supplemented by 2 Gigabit connections on HBAs, switches, and storage targets.

The Fibre Channel Industry Association (FCIA) recently approved going forward with 4Gb development on Fibre Channel end systems and switches. Although not all Fibre Channel vendors are eager to jump into the 4 Gigabit initiative, there are valid technical reasons to double current transport speeds. Unlike 10Gb technology, 4Gb Fibre Channel would be backward compatible with the installed base of 1Gb and 2Gb SAN equipment. This would make it easier for customers to integrate high performance applications with the mainstream SANs they have already implemented.

In addition, doubling the speed of the current 2Gb standard presents far fewer challenges than 10Gb Fibre Channel would entail, enabling a much faster time to market. Finally, 4Gb interfaces on storage targets would enable a more streamlined aggregation of servers to storage ports.

Today, most storage applications do not fully utilize a 1 Gigabit connection at the server. A fatter pipe on the storage array, however, enables more servers to be configured per storage port. This simplifies connectivity while giving customers the flexibility to integrate both high and low performance storage applications on the same SAN infrastructure.

Security

Until recently, Fibre Channel has successfully avoided the security conundrum. As more SANs appear throughout enterprise networks, however, SANs no longer enjoy the inherent security of the data center. Security concerns are thus a testimony to the success of Fibre Channel SANs and the spread of SAN technology into departments, remote branches, and other less secure environments.

To address these issues, Fibre Channel switch vendors are responding with authentication mechanisms borrowed from IP networking, so that only authorized end systems are allowed to connect into the SAN. In addition, vendors such as NeoScale are providing “bump-in-the-wire” products that intercept and encrypt Fibre Channel data as it is written to disk or tape.

Alleviating customer concerns over security for both data center and dispersed storage environments enables Fibre Channel to remove a barrier to adoption and achieve parity with the security mechanisms of mainstream IP networking.

Network Convergence

Similar to security issues, Fibre Channel’s isolation in the data center has allowed it to avoid the mainstream culture of IP networking. Aside from out-of-band management, there has been little need for IP within SANs. IP networking, however, is the transport of choice for 99% of today’s enterprise data communications, and customers have long been seeking ways to leverage their network infrastructures for storage traffic.

As a result, Internet Fibre Channel Protocol (iFCP), Fibre Channel over IP (FCIP), and Internet SCSI (iSCSI) have emerged to bridge the gap between previously insular Fibre Channel and mainstream networking. The current trend in Fibre Channel SAN technology is the integration of multi-protocol support, both within Fibre Channel switches and within storage targets. Far from diluting the efficiencies of Fibre Channel, these new multi-protocol storage capabilities amplify the benefits of traditional SANs and enable maximum utilization of both Fibre Channel and IP assets.

Page 3: SAN Routing

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.

Summary

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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