What's In A Name? -- Differentiating SAN And HAS.

Storage-savvy integrators and enterprise IT management have had SANs and NAS on their radar screens for some time, but the way the technology trends seem currently, definitional issues may begin to cloud the decision making process. Exemplified by the announcements of the Open Storage Network Initiative (see cover story), the distinction between NAS and SAN may begin to blur.

When Fibre Channel was considered the enabling technology for SAN, it was easy to identify a SAN ... that which was FC was also SAN. The interface is distinct from the host interface and carries the speeds necessary to process block level traffic to support a network. NAS offers a fast, almost completely painless; architecture for adding storage capacity to an enterprise or departmental network, facilitating file level transfers that ease the burden of the servers that support applications.

Times Are Changing

Yet the times are changing and Fibre Channel bids fair to become only an enabler for SANs. Companies touting SANs over different, but well-established, communications infrastructures such as Ethernet, Gigabit Ethernet, and IP are circling wagons.

One of the newest companies in this space and a good exemplar of the movement is a startup called Nishan, headquartered in San Jose. (Nishan is an Urdu word meaning mark" or "impact.") With a management team overwhelmingly experienced in the network world, Nishan recently raised $40 million to develop a complete end-to-end solution for the SAN market based on IP and Gigabit Ethernet. They call it Storage over IP (SoW) and it enables IT management to run storage traffic over their existing IP network, (topologically similar to a NAS approach) or a separate dedicated IP network . . . a more conventional SAN topology. Their switching products are expected in about a year. The challenge in the Nishan vision for the IT integrator or specifier is that it eliminates the ability to define SAN by communications infrastructure.

Adaptec is also looking to develop IP and Ethernet products. The company recently announced EtherStorage. This new technology enables block based storage traffic to be transferred over existing P and Ethernet-based networks and is the result of over two years of research and development at Adaptec on future storage fabric architectures. It is a major step forward in bringing the benefits of SANs to a broader market because EtherStorage leverages the existing Ethernet infrastructure and provides storage levels of performance. It retains all the existing networking, interoperability, manageability, compatibility, and cost advantages that have made Ethernet so successful because EtherStorage runs over Ethernet and IP.

New Definitions

It has become comfortable to identify the term SAN with FC communications, but this has historically caused problems... and the problems are coming to roost. One of the problems is labeling a SAN or a NAS device. Some SANs are destined to go over Ethernet lines; NAS already connects over these lines. How does one tell the difference, now? Or is drawing a distinction really worthwhile?

The Storage Networking Industry Association saw the handwriting on the wall some time ago and planned their approach to naming the architectures. In the special CTR supplement developed in cooperation with SNIA in 1999, the organization designated SANs by reference to the communications infrastructure. They note specifically:

"The SNIA definition specifically does not identify the term SAN with Fibre Channel technology. When the term SAN is used in connection with Fibre Channel technology, use of a qualified phrase such as 'Fibre Channel SAN' is encouraged. According to this definition, an Ethernet-based network, whose primary purpose is to provide access to storage elements, would be considered a SAN."

The SNIA definition clearly combines communications structure and management function for the network to delineate SAN and NAS, but the confusion created is certainly not going to speed up IT acceptance of SAN as a solution. It adds an extra stumbling block to a market racetrack already burdened with issues of interoperability, management tools (or the lack thereof), security, and cost.

Not that these burdens are eternal, by any degree. Most of the SAN interoperability issues have focused on Fibre Channel implementation, especially issues of zoning and incompatible interswitch links between FC switch vendors. Such issues were dealt with in the mainstream networking world some time ago.

So how best to address SAN and NAS? A good approach came from analysts and vendors alike. We would step away from the communications substructure and focus on data handling. If the transfers are block level, you have Storage Area Networking. If they are file level, you have Network Attached Storage. This approach gets beyond the issue of enabling technology and gets to functionality.

Whether this represents a complete definition is open to debate and inte rested parties are encouraged to contribute their thoughts. Emails addressed to [e-mail] will be read and considered for publication when I revisit this issue in a future column. The greater question is this: If Storage Area Networking travels on the same pipe (even a bigger pipe) as applications, is the purpose of SAN thwarted?