Fibre Channel network components: a review

Posted on December 01, 1999

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Fibre Channel network components: a review

Pete Passaretti

Reality check: Fibre Channel is here to stay, but it`s far from perfect. Users face a variety of choices to meet a variety of economic and technological challenges, and there`s no guarantee that two Fibre Channel products will be compatible. As a result, end users often rely on third-party integrators to evaluate, test, qualify, and integrate the components that are sold as overall solutions.

In a SAN environment, everyone is essentially trying to accomplish the same things: sharing of operational and functional resources while providing connectivity, simultaneous support for heterogeneous systems and storage, management of the entire environment, and scalability. It`s also important to deliver value-add functions, such as LAN-free and server-free data movement.

A first step is to understand connectivity and interconnectivity devices, including hubs, switches, routers and bridges, and gateways. Once you get past initial specifications of device-level connects—host bus adapters (HBAs), cables, MIAs, GBICs, etc.—you`re faced with evaluating core backbone components.

Hubs

A hub is a basic connectivity device allowing a single point of connection for multiple links. A Fibre Channel hub can be used to support media transitions, from copper to optical via MIAs and GBICs. Hubs are available from multiple vendors, including Atto Technology, Emulex, Gadzoox, and Vixel. Typical hubs provide from five to eight ports.

Although they provide a high degree of connectivity capability, hubs subject the entire network to loop initialization primitives (LIPs), which occur when a device or port connected to the hub is reset, shut off, or re-initialized. When this occurs, the entire loop environment must be re-initialized, which may result in data loss.

Switches

While a switch is similar in function to a hub, it`s a more intelligent device that evaluates data packets as they pass through. A switch then determines the destination and routes the packets via the fastest route available. Because each port is isolated from the others electronically, switches are not susceptible to LIP problems. A switched Fibre Channel environment is known as a fabric.

Switches are available from multiple sources in various numbers of ports (typically between 8 and 64 ports). Vendors include Ancor Communications, Brocade, Gadzoox, McData, and Vixel.

Routers and bridges

A router, also frequently referred to as a bridge, enables the connection of two distinct elements. For example, a bridge can provide connectivity from a Fibre Channel connection to a SCSI channel, letting SCSI components operate in a Fibre Channel environment. A router allows multiple SCSI channels to be connected to a Fibre Channel environment via a single port. Some advanced routers allow multiple SCSI channels to connect to multiple FC ports without requiring a hub or a switch. Routers deliver the connectivity and heterogeneity needed for SAN and offer options that can provide value-add functions such as server-free data movement. Router and/or bridge vendors include Atto Technology, Chaparral, Crossroads, and Pathlight.

Gateways

Gateways are a relatively new type of interconnectivity device, combining some of the capabilities of hubs, switches, and routers in a single device usually incorporating a middleware type of SAN management. Gateways provide multiple direct connections for hosts and devices using a range of interfaces, as well as interconnectivity for integrating heterogeneous storage systems and operating systems.

A gateway automatically analyzes and reacts to SCSI and Fibre Channel commands and recognizes the attached hosts, storage devices, and interfaces. Gateways are designed to meet the need for resource sharing with multiple levels of access control. Gateways isolate storage traffic from application traffic, supporting LAN-free and server-free configurations. Also they enable end-to-end management of the entire SAN, including gateways and other attached devices. Gateways are currently available from Pathlight.

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In a heterogeneous environment, key connectivity is put to its best uses.

Pete Passaretti is vice president of OEM sales at Pathlight Technology (www.pathlight.com), in Ithaca, NY.


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