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Script: SAN audio primer

Network World Fusion

As corporate America turns to databases, streaming media, online transaction processing and other bandwidth-intensive technologies, ordinary servers and peripheral storage devices simply can't handle the load. Storage area networks, or SANs, are one possible answer.

Unlike stand-alone servers, a SAN distributes resources over a scalable, redundant network of servers and storage devices. This lets large numbers of users quickly and simultaneously access data without creating bottlenecks. SANs can also back up data with a minimal impact on network throughput, owing to the distributed nature of SAN architectures. Another plus is that the devices attached to the SANs can be centrally managed, instead of on a per-device basis.

At the heart of the SAN concept is Fibre Channel, a very fast interconnection technology that currently supports speeds of up to one gigabit per second, at distances of up to 10 kilometers. This is generally faster than SCSI-based storage found in ordinary PCs and servers, which supports maximum data transfer rates of 160 megabits per second. Another type of storage common in LANs, Network Attached Storage, offers Fast Ethernet speeds, but there is no centralized management features as there are in SANs.

How does a SAN architecture work? Storage devices - such as RAID arrays or tape drives - are attached to servers using Fibre Channel. These high-speed connections enable any-to-any communication among the devices on the SAN. Another benefit: There are alternate paths to connect the servers and storage, so if a server drops out, another can allow access to the stored data.

Your network may already have many of the pieces needed to make a SAN. Typically, an existing network will be attached to groups of servers and storage devices using Fibre Channel adapters. As storage needs grow, Fibre Channel hubs and switches can be added.

Want to add a new drive or disk array? No problem - the device doesn't have to be hooked up to a specific server, it can simply be added to the storage network and accessed from any point. Older SCSI-based storage devices, such as tape drives, can be plugged into the SAN using Fibre Channel-to-SCSI adapters, which are typically rack-mounted units with several SCSI and Fibre Channel ports.

Using long-distance carrier technologies such as ATM, large SANs can theoretically span the planet. Unlike LANs, SANs distribute processing duties throughout the network, instead of on the individual file servers. This increases overall data transfer speeds and reduces bottlenecks, making for a smooth end-user experience.

But SANs aren't for all types of organizations. The brain of a storage area network is software. In order to manage all the different types of devices that make up a SAN, customized software is required. This can be expensive and complex to implement.

But that's not all: the SAN software issue is complicated by a lack of standards. This means gear and software from different vendors might not work together.

While Fibre Channel does have a standard, vendors interpret it in different ways. In addition, SAN vendors have not agreed on related ground rules, such as standards for device management, security and storage. Many have created their own standards, which has led to more interoperability problems. It is this uncertainty about standards, along with cost and complexity, that has kept many potential SAN customers on the sidelines.

What does the future hold for SANs? Certainly more growth as Internet-driven storage needs explode. Faster speeds are in the pipeline, too - the Fibre Channel standard will support up to 4 gigabits per second in the near future, and 10 gigabit Fibre Channel gear is on the horizon.

On the standards front, industry consolidation and cooperation among vendor organizations has led to some progress. But until the standards issue is resolved, experts say totally certified turnkey solutions - incorporating software, hardware and vendor know-how - are the best choice for SAN projects.

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