Chapter 4. Introduction to Fibre Channel Storage Area Networks

   

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This chapter is an introduction to storage area networks (SANs) in general and Fibre ^[1] Channel (FC) storage area networks in particular. Although storage area networks can and will be built with technology other than Fibre Channel, the vast majority of storage area networks are and will continue to be Fibre Channel based for quite some time. Accordingly, this chapter describes Fibre Channel in detail. Storage area networks based on other technologies, such as iSCSI, are discussed in Chapter 8.

^[1] The spelling was changed from Fiber to Fibre in an attempt to denote the fact that Fibre Channel can operate over copper as well as optical (particularly fiber- optic ) media.

Fibre Channel is an interconnectivity technology that merges aspects of high-speed input/output and networking. As this book goes to press, FC SANs have speeds of 1 Gbps (gigabits per second), and commercial deployment of SANs with speeds of 2 Gbps is growing.

Devices in Fibre Channel terminology are called nodes . Again, this is similar to the terminology of a node in an IP (Internet Protocol) network. A Fibre Channel node can have multiple ports, just as an IP node can have multiple IP addresses. The difference is that whereas each FC port is a physical entity, each IP address is a logical entity. Each FC node has a unique 64-bit World Wide Name (WWN) assigned by the manufacturer. This is similar to the unique MAC (Media Access Control) address assigned by Ethernet network interface card manufacturers. Each port in a switched-fabric FC SAN has a 24-bit port ID. The ports in an arbitrated-loop FC SAN have an 8-bit address. When the arbitrated loop is connected to a fabric environment, the fabric switch makes the 8-bit address appear to be a 24-bit address. Both these 24-bit and 8-bit port IDs and addresses are dynamically assigned. The concept of ports and their various different types is explained in Section 4.5.

The need for Fibre Channel is explained next . Following that discussion, SANs are compared with network-attached storage, which was covered in Chapter 3. Then the chapter takes a top-down approach that introduces Fibre Channel topologies, moves on to discuss the underlying protocols, and finally describes the various building blocks (including devices) that constitute a Fibre Channel SAN.

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