Storage area network (SAN) architecture efficiency

A storage area network (SAN) overcomes cumbersome, complicated, multiple-server environment problems by moving storage resources off of the common user network and reorganizing storage components into an independent,

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high-performance network. Storage performance is enhanced using a fast interface, such as Fibre Channel (FC), that connects storage servers and storage devices through an array of switches and hubs to form a fabric that supports both redundancy and high availability. SAN technology also supports important storage features, including disk mirroring, data backup, restore, data archiving/retrieval and data migration.

A storage area network is typically assembled using three principle components: cabling, host bus adapters (HBAs) and switches. Cabling is the physical medium used to interconnect every SAN device. SANs can use both copper and optical fiber cabling, though the choice of medium depends on the speed and distance requirements of the SAN. Slower or shorter distance connections can be made through copper cables, while faster or longer distance connections are achieved through optical cables. Optical fiber cables can be single mode or multimode. Single-mode (or monomode) fiber is designed to carry only one light signal over long distances, while multimode fiber can carry multiple simultaneous light signals over short distances. Optical fiber also uses several different kinds of connectors, so it's important to select connectors that are compatible with other components of the fabric.

Each server or storage device in a storage area network fabric requires an HBA. The HBA can exist as either an expansion card that fits into a compatible expansion slot in a server, or it may be a chip integrated directly into the server or storage device. An HBA typically offloads data storage and retrieval overhead from the local processor, improving the server's performance. Cabling is used to connect the HBA's port to a corresponding port on a switch.

A switch is used to handle and direct traffic between network devices. The switch accepts traffic, and then relays the traffic to the port where the intended destination device is attached. In a SAN, each storage server and storage device connects to a switch port. The switch then relays traffic to and from specific devices across the SAN -- this series of switched interconnections form the SAN "fabric," which can easily be scaled or changed. An intelligent switch serves the same basic functions but incorporates high-level SAN features like storage virtualization, quality of service , remote mirroring, data sharing, protocol conversion and security.

Click for the next installment of SAN 101: SAN connectivity and protocols

This tip originally appeared on SearchStorage.com.

This was first published in November 2006

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