W ith storage-performance and storage-space dilemmas all too common for sites running memory-killer applications like imaging, transaction processing, multimedia, data warehousing and Internet downloads, storage area networks (SANs) are widely discussed and equally in demand.

As networks continue to expand and applications churn more and more data, increasing amounts of high-performance storage subsystems are needed to keep pace. SAN solutions address these rapidly growing storage needs.

As processor and application performance have increased exponentially over the last decade, UNIX and Windows NT distributed platforms have largely replaced data-center-centric computing models. But during this same time span, improvements in file access and data-transfer techniques have been minimal.

Now, they have reached the critical point where server-to-storage communications have become the major roadblock to improved systems' availability and performance. SAN technology is changing this, deploying mainframe-class, host-to-storage functionality to the enterprise network environment at open systems price-points.

A SAN is a dedicated network-type communications link between multiple servers and storage devices. Its high bandwidth and high availability provide improved server-to-storage efficiency and throughput while freeing the LAN from the large packet data transfer chores and the bandwidth-intensive overhead associated with storage tasks. The removing of storage-access functions provides a big boost to overall network performance.

Now ...

In the traditional approach, a storage device (e.g., disk, tape, RAID) is typically attached to an individual server via a point-to-point connection, such as a SCSI bus. With this one-to-one structure, each server utilizes its own unique data-management architecture, segregating storage-management tasks and making centralized control nearly impossible in an open-systems environment. In fact, when a site requires additional storage capacity, MIS administrators often turn to offline expansion on each server as the safest and simplest solution.

Additionally, file accesses and data transfers between storage devices must travel the busy LAN pipeline, straining bandwidth resources and resulting in sluggish response times across the network.

Overall LAN degradation caused by extensive server-to-storage communications over the network is common and not easily remedied in present SCSI-bus configurations. Due to restrictions in cable lengths, bandwidth and connectivity, MIS administrators are hard pressed to break this data-traffic logjam.

... and Later

This is the year SANs cross the chasm between early adopters and general market acceptance. Two years ago, less than 10 percent of IT administrators in a distributed LAN environment understood storage area networks. Today, SAN stories fill the cover pages and storage sections of most IT publications and SAN benefits are being discussed at all major industry events.

As SANs are integrated into existing enterprise networks, users gain faster access to gigabytes of data, a higher level of data availability and a more reliable, fault-resilient server-to-storage-device hardware path than was previously possible.

Most early SAN deployments concentrated on enhancing storage-to-network data transfers by replacing SCSI buses with Fibre Channel I/O paths for communications with disk storage devices. These installations received the immediate benefits of increased bandwidth (100MB) for faster file throughput over longer distances (10 kilometers) than was possible with SCSI-buses (80MB and 25 meters, respectively).

Today, new software is enabling additional SAN benefits like remote tape vaulting and disk mirroring, backup/restores with dynamic tape drive allocation and high-availability clustering. In the future, SANs will turn storage into an enterprise-wide commodity allocated to applications when and where needed.

With a SAN, storage devices are moved off the server backplane and onto their own high-speed network. When this is done, overall LAN performance improves because it is freed from bandwidth-intensive storage functions. Any host on the network can access any storage device and its stored files without interfering with LAN traffic.

Various storage units (disks, tape libraries, RAID) can be mixed and matched and they can all communicate with multiple hosts and with each other. The storage subsystem