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Ethernet Technology Grows Up--And Out

Developments on several fronts could give iSCSI the power to muscle in on higher-end Fibre Channel SANs.

Your SAN might be getting a speed boost soon. New 10 Gigabit Ethernet-based systems can reach throughput levels that previously were reserved for Fibre Channel architecture, possibly making Ethernet a more attractive option for high-end storage.

Big-name vendors are entering the race with a new wave of "enhanced Ethernet" networking and storage technologies, tapping lower-cost 10-Gbps Ethernet chipsets and hardware. And they're gunning for a SAN near you.

Before they arrive on your network, however, you'll need to figure out if these offerings--which include Ethernet extensions for the data center from Brocade, Cisco, and others, as well as Fibre Channel over Ethernet, or FCoE--provide an adequate ROI. What are the risks? And where does amped-up Ethernet leave iSCSI SANs, which tap TCP/IP and standard Ethernet to haul data at thousands of small and midsize organizations?

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It's easy to see why iSCSI is popular with the masses. It runs on standard Ethernet networks, and IT personnel without Fibre Channel experience can attach iSCSI servers to block-based storage devices. If you know Ethernet and TCP/IP, you can build an iSCSI SAN and inexpensively attach servers to shared storage resources.

Deployments of iSCSI have experienced rapid growth in a wide variety of applications, including file servers, Microsoft Exchange and Microsoft SQL Server databases, and VMware ESX servers. A raft of iSCSI target systems are available from major vendors including Dell EqualLogic, EMC, Hitachi Data Systems, IBM, and NetApp.

Still, iSCSI hasn't joined Fibre Channel in legacy enterprise SANs and higher-performance apps for a couple of reasons. First, most iSCSI SANs run on Gigabit Ethernet today, versus 4-Gb or 8-Gb speeds for Fibre Channel. ISCSI uses as a transport TCP/IP, which introduces overhead from protocol processing and affects end-to-end latency and throughput compared with Fibre Channel. Second, the ecosystem of tools and tactics for deploying and managing Fibre Channel SANs is mature and pervasive. ISCSI SANs fall behind Fibre Channel in this area, which is a crucial consideration for storage admins.

Wide adoption of 10-Gbps Ethernet will boost iSCSI's popularity in enterprise storage, but even with better wire speed, protocol overhead and management issues remain.

Enter FCoE

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Fibre Channel over Ethernet, now in development and before the T11 standards committee for ratification, is being promoted by major vendors, including Brocade, Cisco, EMC, Emulex, IBM, Intel, NetApp, QLogic, and Sun Microsystems. FCoE uses enhanced Ethernet as the physical network transport to deliver the standard Fibre Channel payload, skipping the overhead of TCP/IP, and is designed to look and act like native Fibre Channel to the upper software layers, including the operating system, applications, and management tools. Fibre Channel services such as discovery, worldwide name addressing, and zoning all work the same way in FCoE as in native Fibre Channel. However, because it doesn't use TCP/IP, FCoE traffic isn't routable across IP networks. FCoE is designed exclusively for low-latency, high-performance, Layer 2 data center networks.

How iSCSI And FCoE Stack Up

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