A key decision in designing a SAN is whether to go with a hub, switch or director as the central unit. Over the last couple of years the three types of devices have become strongly differentiated, although there are still a number of products that fall in between.

A hub is the least expensive approach to building a SAN and uses the Fibre Channel Arbitrated Loop (FC-AL) protocol, which is widely supported. The hub's disadvantages include sharing the bandwidth and few features for SAN management. According to EMC (www.emc.com) a hub is best suited to applications with a small number of hosts where performance is not a major concern.

Switches cost more than hubs, but they offer better performance, and more management and availability features. Their disadvantages include a low number of ports (compared to a director) and they can be complex to scale as storage needs grow. Switches tend to work best with few hosts, but performance is important.

Directors are the most expensive of the three, but also offer the largest number of ports and, typically, advanced management and availability features. They are generally used in large enterprises with centralized infrastructures, often for mission critical or high-performance environments.

Obviously, the choice for your central element is a matter of these considerations and more. EMC discusses which to choose in a white paper titled, "Designing an enterprise storage network to manage growth and change", which is available

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on the company's web site at www.emc.com

Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.

This was first published in October 2002

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