Ethernet's Place in Future Storage Solutions

Several months ago, a columnist in one of the weeklies expressed doubt that companies need yet another network beyond their typical Ethernet LANs. His contention was that the arrival of Gigabit Ethernet made building fabrics with fibre channel unnecessary. Many readers wrote in to describe the benefits of fibre channel: greater attachment rates, longer distances for connections, fabric topologies, better fault tolerance and redundancy, and greater frame-based data throughput. (Note: Cost was NOT on the list of fibre channel benefits.)

Fast forward to Adaptec's May announcement about its new SCSI over Ethernet EtherStorage technology and demonstration of a prototype Storage Area Network (SAN) built with a standard Netgear 2-port Gigabit, 10-port 10/100 switch, and Ethernet cabling and adapter. The product will be available in about a year—when host bus adapters and target devices will also be available.

What EtherStorage does is let block-based storage traffic move over existing IP and Ethernet-based networks. And because EtherStorage uses existing Ethernet infrastructure, it's cheap to implement. EtherStorage works with standard Ethernet switches, hubs, and cables. Therefore, if you don't need large device attachment rates, you can implement both fabric and fault-tolerant (dual-channel) solutions to storage devices over Ethernet. The technology works best on small networks or in departments; Adaptec is targeting ISPs, Web hosting sites, and small Windows 2000 and Windows NT networks with 10 to 30 servers.

EtherStorage uses protocols that encapsulate SCSI commands and data and sends them over an Ethernet network. The protocols are divided into two layers, a session layer and a transport layer, both of which run over the IP networking layer. A protocol called SCSI Encapsulation Protocol (SEP) in the session layer packages SCSI commands and data and sends them over any reliable transport layer.

Adaptec sees two possible transport layers: the SAN transport protocol (STP) and TCP. STP would be used in a SAN/LAN application that taxes bandwidth, CPU utilization, and latency. STP offers substantial throughput through a Gigabit Ethernet pipe. TCP would be used in a WAN application in which the data is routed over a large complex network. WAN applications might include SAN-to-SAN connectivity and remote mirroring for disaster recovery.

Adaptec is part of an Internet Engineering Task Force (IETF) standards committee that addresses the issues involved in Gigabit Ethernet storage networking. The committee includes 3Com, Cisco, Hewlett-Packard (HP), IBM, Quantum, and others who are developing a standard for SCSI encapsulation. Adaptec bets that Gigabit Ethernet is about to become a commodity. (I bet the company's right.) The standard for 10GB Ethernet is reaching production stage, and development has begun on the specification of a 100GB Ethernet technology.

In a couple of years, we might well see two types of SAN solutions: fibre channel in the enterprise and SCSI over Ethernet in smaller local settings.

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