SAN connectivity guide - Fibre Channel, Ethernet and iSCSI

By Stephen J. Bigelow, Features Writer | Jul 6, 2009

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A storage area network (SAN) organizes a broad assortment of storage devices into a single storage resource that can then be provisioned, allocated and managed for the entire enterprise. Although issues like storage capacity performance and management often receive the most attention, the connectivity between each SAN device plays a critical role in successful SAN deployment.

Each switch and storage system on the SAN must be interconnected -- usually through optical fiber or copper cabling -- and the physical interconnections must support bandwidth levels that can adequately handle the peak data activities that occur. This overview details the role of Fibre Channel, Ethernet and iSCSI connectivity on a SAN.

Fibre Channel
Fibre Channel is the quintessential SAN interconnect and virtually every storage switch and storage platform provides Fibre Channel ports. Multiple Fibre Channel ports support simultaneous data streams, but individual ports can often be aggregated into groups for even higher effective bandwidth. Servers and other devices can also be fitted with Fibre Channel host channel adapters to enable an Fibre Channel interface.

As a serial interface, Fibre Channel bandwidth is denoted in Gbps. Early Fibre Channel implementations ran at 1 Gbps per port before doubling to 2 Gbps and then 4 Gbps. Another transition to 8 Gbps is beginning but mainstream adoption is not expected until mid or late 2009. Also, 10 Gbps is used in interswitch links to connect Fibre Channel switches to each other. Fibre Channel operates with numerous protocols, most notably SAS and IP.

Fibre Channel can use several types of physical media. Twisted pair cable is used to cover relatively short distances at low speeds between Fibre Channel devices. Coaxial cables generally offer better shielding against signal interference and can run across somewhat longer distances. Optical fiber is routinely used to carry the fastest signals across distances up to 10km.

Ethernet
While Ethernet connectivity is generally used on the greater local area network (LAN), its use in the storage area network has been limited by its relatively slow bandwidth.

Traditional Ethernet ports support 10/100 Mbps -- far slower than Fibre Channel. This had limited Ethernet in the SAN to basic management tasks. For example a storage device or switch might include a single Ethernet port that connects the device to the LAN where an administrator can manage the device across it. Ethernet typically uses two protocols; Transmission Control Protocol (TCP) which handles the organization of data into packets and Internet Protocol (IP) which handles the way those data packets are addressed. In fact, the terms "Ethernet" and "TCP/IP" are often used interchangeably.

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