SANs Are Here - Technology Information

Computer Technology Review, Sept, 1999 by Peter Tarrant

With a SAN, storage device(s) are moved off of the server back-plane and onto their own high-speed network. When this is done, a number of things occur:

* 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, and RAID) can be mixed and matched; they can all communicate with multiple hosts and with each other.

* The storage subsystem is isolated from the operational limitations of the server and LAN traffic constraints.

* Alternative data paths are established between storage device(s) and server(s), fostering fault-tolerant operations.

* Storage components can be easily managed and centrally administrated.

* Storage is externalized; therefore, storage capacity can be easily scaled in accordance with storage needs and is not tied to server performance.

The net result is a SAN that creates a shared storage repository attached to a high-speed pathway (channel). This channel is optimized to handle the fast throughput and large file size transfer requirements demanded by today's high-end storage tasks associated with applications like video, CAD, OLTP, and data warehousing. The SAN will eventually (when all the software becomes available) allow for universal data sharing across all platforms on the enterprise-wide network and handle high-bandwidth storage management functions like archive/ retrieval, backup/restore, and disaster recovery.

SAN Components

The SAN consists of servers, network interface cards, Fibre Channel interconnects, storage devices, and either copper or optical cabling. Intelligent switches make up what is commonly referred to as the Fabric. Most SAN implementations are expected to employ Fibre Channel fabrics, as they offer the bandwidth, scalability, distance, reliability, and investment protection sought by many users.

SANs are not necessarily synonymous with Fibre Channel. Yet, so intriguing is the potential performance promised by Fibre Channel vs. other bus-connections (such as SCSI and ESCON) that FC has vaulted to the forefront of SAN developments. Switched Fibre Channel fabrics provide unparalleled levels of flexibility, high-through-put, and inherently fault-resilient access paths, rivaling mainframe-level host-to-storage communications. These switched fabrics support modular scaling of devices and up to 16 million device addresses. The channel handles multiple protocols and 100MB/sec, full-duplex bandwidth over each switch path. The Fibre Channel switches can be cascaded to provide dramatic capacity and aggregate performance scaling.

Fibre Channel's purpose is to address server-to-storage interface limitations. Its throughput capability greatly enhances information transfers at any site where high-end applications (e.g., imaging, video, OLTP, databases, and CAD/CAM) are outpacing storage system performance. The extended host-to-storage device connectivity distances that are possible with FC (over 6 miles) are ideal for applications like remote backup, archiving, and mirroring for disaster recovery purposes. In addition, the Fibre Channel support for long-distance ATM connections is enabling a whole new class of enterprise-wide storage applications.

Fibre Channel switches assure high availability network-to-storage environments. These switches provide for highly resilient modes of operation, storage device scalability, and easy hot-plugging/unplugging of devices. This means that reconfiguration of the storage component is simple and does not affect SAN or LAN operations. Security and isolation between functions is another advantage of switched fabric SANs. Fabric switches provide the self-learning and self-healing features to tackle any array of storage intensive management tasks like full network backup, remote vaulting, and hierarchical storage. Fabrics composed of multiple switches enable Fibre Channel networks to grow to very large sizes, thereby enabling continuous operations with centralized control over distributed storage resources.

Why Are SANs Catching On?

As business operations keep expanding, more and more mission critical data is generated that must be kept online and available. In fact, the amount of data that has to be stored and managed is now doubling almost every 12 months. This data eventually requires additional server storage space. The most common non-SAN alternatives to meeting these increased storage needs are:

* Adding another individual server disk;

* Replacing the existing server disk with a larger unit;

* Adding another server "box."

These are all expensive and time-consuming options. With a SAN solution, storage capacity can be scaled as needs dictate without interrupting network service, without reconfiguring hassles, and without regard to the server's performance and/or enclosure limitations. Administrators want a storage solution that they can use with their existing networks, thus protecting investment in current IT systems. Everybody wants a storage system that is easy to manage, easy to scale, and easy to integrate into their existing structure. SANs do all of this. They offer centralized storage management, independent storage subsystem scalability, and they are quickly integrated into most major network operating platforms such as Unix and NT.