SANs and WANs converge into SWANs

Posted on November 01, 1999

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SANs and WANs converge into SWANs

Several technologies are still required to provide the kind of functionality required for next-generation global SANs.

Felix Diaz

The importance of storage area networks (SANs) to enterprises of all sizes has placed it at the forefront for many IT managers. Now, the SAN market is on the verge of another phase, and IT managers and storage integrators again will need to combine several technologies to provide the kind of functionality required for global SANs--networks without borders.

SANs give organizations the ability to scale their storage facilities to meet what is seemingly a never-ending need to store more data. In addition, SANs can give access to critical data to anyone in the enterprise no matter where they`re located. Distributing an organization`s data storage facilities also has inherent advantages for security and disaster recovery. Replicating data in geographically distinct areas will safeguard the data should a catastrophe occur or the security of the data be breached in a certain location.

As more and more organizations have implemented local SANs, Fibre Channel has emerged as a critical technology. Its communication speed in the range of gigabits per second and the high number of online transactions per second that can be supported on a Fibre Channel SAN make it a logical selection. Another advantage is its ability to effectively scale to support very large networks with many interconnections.

But perhaps the capability that weighs most heavily in Fibre Channel`s favor is not what it is, but what it isn`t. Fibre Channel isn`t just a peripheral I/O interface. It`s a networking technology that lends itself effectively to storage applications. Fibre Channel`s support for the Internet Protocol (IP), as well as for peripheral I/O protocols like SCSI, make it a keystone technology in the implementation of local SANs and emerging next-generation SANs.

No SAN is an island

As local SANs proliferate in enterprises, IT managers are realizing that connecting these SANs, which may be separated by long distances, can bring additional value to the organization. Separate and distinct local SANs may serve the needs of a limited group within the enterprise, but they only scratch the surface when it comes to benefits for the entire organization.

The next phase of SAN evolution is the removal of geography from the equation by interconnecting local SANs. Instead of an organization deploying several distinct storage networks for localized purposes, wide area networking (WAN) technology can be used to deploy one interconnected "storage WAN"--or SWAN--that will serve all of the data storage needs of the enterprise. SWANs will maximize the inherent value of the information shared by the organization in applications such as data warehousing and data mining.

Considering the significant investment organizations have already made in SANs and their high local communication speeds, broadband technology will be needed to interconnect SANs in a SWAN.

Using SONET as the interconnection pipe can be ruled out because it`s not capable of the end-to-end management needed in a SWAN. SONET is basically a transport mechanism, and although it`s capable of managing certain aspects of individual links, it can`t manage an entire connection made up of several links. In addition, wide area communication providers are not offering SONET as a service. For several reasons, carriers have chosen to offer other types of broadband communications services, such as asynchronous transfer mode (ATM).

With speeds in the gigabits per second range, ATM has the bandwidth needed to connect local SANs. Because it`s a networking technology, not just a transport mechanism, an ATM connection can be well managed and controlled. And ATM services are now at economically efficient rates.

In some aspects, the functional underpinnings of Fibre Channel and ATM are already converging. Certain concepts like virtual interfaces in Fibre Channel and virtual connections or circuits in ATM are very similar in intent. In time, these concepts will provide an effective way to combine the best of both technologies in global storage networks.

For example, the concept of a virtual interface beginning with Fibre Channel and running through an ATM wide-area connection can eliminate one of the bottlenecks encountered in traditional network server architectures. Historically, network servers have had one TCP/IP protocol stack, which was tied to the processing of the operating system on the server. This situation leads to a bottleneck that slows down network performance. Since many online transactions take place at the same time, they can`t all use a single protocol stack. Some transactions must wait and, as a result, network performance degrades.

By mapping the concept of a virtual interface onto ATM`s concept of virtual circuits, each process on a network server can have its own socket, so to speak, and process the protocol stack independently of each other. This enables processes on separate servers to communicate directly with each other and with the server`s underlying hardware. Each process can be allocated its own small-scale communication pipe.

Hardly an ugly duckling

As interest in SWANs grows, the inadequacies of simply using a network server as the interface among multiple local storage networks will become apparent. Servers were never intended for such a role.

SWAN gateways will perform many of the same tasks that networking gateways have handled, such as protocol conversions, filtering, IP routing, security checking, and packet forwarding. Although SWAN gateways will be the bridges between local SANs, IP will be the glue that holds the entire fabric together. In a SWAN, Fibre Channel and ATM will have their own respective protocol stacks, but IP will provide commonality between the two environments.

In addition, IP will provide the management capabilities for geographically dispersed SWANs. And, with Java-based management tools, local SANs can be managed remotely over the facilities of an enterprise SWAN that stretches around the globe.

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Local storage area networks are typically not linked, and can be separated by long distances.

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A storage wide area network (SWAN) links local SANs via wide area network technologies such as ATM.

Felix Diaz is chief technology officer at Interphase Corp. (www.interphase.com), in Dallas.


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