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The anatomy of a SAN: Fibre Channel SAN explained

What you will learn in this tip: Fibre Channel SANs are a popular choice for many organizations. In part one of our series on Fibre Channel vs. iSCSI SANs, we examine the components of a Fibre Channel

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SAN to help you decide if it's the best SAN technology for your organization.

There are lots of questions about which storage area network (SAN) technology makes the most sense for small- to medium-sized businesses (SMBs). The most commonly asked question is which SAN technology is better: Fibre Channel (FC) SAN technology or iSCSI SAN? There is no correct single answer. Neither Fibre Channel or iSCSI fits all types of SMBs. Each technology has its supporters and detractors and there are definitive differences between these two SAN technologies. But those differences have narrowed considerably with the latest generations of iSCSI and Fibre Channel technology. Most of the debate is derived from out-of-date information or misconceptions.

Before you decide on whether or not to use Fibre Channel or iSCSI SANs for your SMB data storage environment, you must first understand today's current SAN level setting and the features of Fibre Channel and iSCSI SANs. This tip outlines today's SAN technology and the features of Fibre Channel SANs.

Current SAN level setting

A SAN is essentially a switch-based technology that interconnects and switches multiple physical servers, virtual machines (VMs), and applications to external storage. Storage administrators are often confused and think that the SAN storage array is the SAN. In reality, the SAN storage array is just one piece of the SAN. A SAN allows more hosts to access that SAN storage array than the array has physical ports.

The anatomy of a Fibre Channel SAN

Fibre Channel technology is one SAN technology you can choose for your SMB. Fibre Channel is an extremely stable mature layer-2 switching SAN technology, and the predominant SAN variant today in the enterprise. It preceded the iSCSI standard by nine years, and the Fibre Channel protocol (FCP) is the only commercially utilized protocol on Fibre Channel. FCP is the standard storage SCSI storage protocol wrapped in Fibre Channel frames.

There are three physical components to a Fibre Channel SAN. The first piece is the Fibre Channel host bus adapter (HBA), otherwise known as the initiator. An HBA is either a PCIe card or chip residing on the host motherboard. It embeds the FC standard into silicon, minimizing host resources. A software driver resides on the host as well.

The second piece is the Fibre Channel switch. The FC switch is a non-blocking (no internal oversubscription of bandwidth) layer-2 switch with extensive management capabilities that conform to the FC standard. The variation of the FC switch is the FC director. The FC director is a large port count non-blocking switch; it has high-availability (HA) with no single point of failure and enterprise class feature functions (such as encryption, virtualized SANs, gateways to other networks, etc.).

The third piece is the objective of the HBAs called the FC storage target port, or target. It is the external storage connection to the Fibre Channel SAN (FC fabric.) The target storage port provides the address (which is built into the silicon) or worldwide name (WWN) address of each target storage port. The hosts each have their own unique WWN address that allows them to connect to target storage for each read or write session. One key piece of software is Fibre Channel SAN multipathing code that resides on each host accessing the external storage. This allows each host to have multiple paths to its target storage for primarily path failures and in some cases, load balancing and performance aggregation.

FC initiator, target, and switch port bandwidth are currently available as 8 Gbps or 4 Gbps interoperable variants. They're also interoperable with previous 2 Gbps but not 1 Gbps variants.

In the next part of our series on Fibre Channel vs. iSCSI SANs, we'll look at the components of an iSCSI storage area network.

About the author: Marc Staimer is the founder, senior analyst, and CDS of Dragon Slayer Consulting in Beaverton, OR. The consulting practice of more than 12 years has focused in the areas of strategic planning, product development, and market development. With more than 30 years of marketing, sales and business experience in infrastructure, storage, server, software, and virtualization, he's considered one of the industry's leading experts. Marc can be reached at marcstaimer@mac.com.


This was first published in September 2010

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