Evaluating the requirements for the storage network backbone

Computer Technology Review, June, 2004 by Eric Blonda

It was only a few years ago that storage area networks (SANs) were exclusive to early-adopter technologists and those who could justify the return on investment (ROI) from what would be a large investment in hardware, software and expertise. Now that SAN ROI is considered proven and applicable to most enterprise data centers, SANs are one of the key information technology assets accelerating productivity and trimming the bottom line for today's enterprise. Through this transition, SAN technology has evolved, with some of today's most significant technology evolution occurring not in storage or application resources, but in the network that connects them.

Historically, the network connectivity portion of the SAN has been purchased in conjunction with the storage array. Each time IT purchased new storage, it would be accompanied by network components (switches, cables, etc.) to allow connectivity to the application hosts. This incremental approach to storage networking was appropriate for the early stages of SAN deployment, as SANs were usually tactical rollouts associated with particular applications. However, project-oriented rollouts are giving way to a more strategic "backbone" architecture that is independent of particular storage and server resources and allows higher disk utilization through increased consolidation. As enterprise IT professionals begin to architect the storage network backbone, it is crucial to consider fundamentals that will serve through several data center lifecycles, including scalability, modularity, interoperability, visibility and control.

Scalability

To this day, many SAN deployments have consisted of tactical, project-oriented architectures. Built upon 8- and 16-port fabric switches, these "SAN islands" provide effective connectivity for a particular application or storage resource, but do not scale to meet enterprise-class, long-term requirements. To examine the scalability limitations of today's fabric switches, it is important to understand the requirements for inter-switch links (ISLs) in typical core/edge fabric architectures.

IT professionals are now considering the opportunity to build a strategic, independent network infrastructure that will scale to meet the enterprise's needs for the next several years--the storage network backbone. The storage network backbone provides connectivity for hundreds of storage and application resources without wasting costly ports to connect other switches.

The strategic independence of the storage network backbone has empowered enterprise IT professionals to build and manage a more universal, utility-based infrastructure that can scale beyond the limitations of traditional SAN fabrics. While there will always be tactical decisions based on individual SAN applications, and those applications may require specific network components for support, the most strategic network is one that can universally support a diverse set of requirements now and into the future.

Interoperability

A main focus of the storage network industry over the last few years has been to promote overall interoperability among SAN components. In order to break away from the exclusive "early-adopter" stigma, SAN deployments are expanding beyond unique and specific interoperability certifications, where connectivity purchases were an "accessory" to disk purchases. Traditionally, SAN configurations have been built using a series of "interoperability matrices" that include storage subsystems, host operating systems, HBAs and any other components in the data path. Referencing a matrix from one or a number of SAN vendors has traditionally been necessary for support agreements, but with the evolution of standards and the sheer volume of SAN components and versions, SAN interoperability and support has been elevated to a more mainstream implementation. It is no longer realistic to expect SAN architects to cross-reference interoperability matrices (some of which are nearly 1,000 pages), where vendors are adopting a more universal level of support.

Modularity

Network growth not only means being able to satisfy higher port count requirements, it also means being able to accommodate future rates, protocols and services. While the vast majority of today's storage networks are being connected via 2GB Fibre Channel, enterprise IT organizations are anticipating the deployment of 4GB and 10GB Fibre Channel, iSCSI, Fibre Channel over IP and network-based storage services. However, building standalone networks for each new rate, protocol and service contradicts the strategic goal of building the storage network back-bones as an independent utility, and can significantly reduce the ROI associated with network infrastructure purchases.

The goal of the storage network backbone architecture is to be modular enough to accommodate future network directions in the least disruptive and most cost-efficient manner possible. In order to do so, the storage network must offer new levels of flexibility, fault tolerance and investment protection.