Exploding the "open" SAN myth

Posted on August 01, 1999

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Exploding the "open" SAN myth

Kirby Wadsworth

Organizations want to believe they are operating in a fully open storage environment, where mixing and matching storage components--without regard to vendor or device specifics--is possible. But when organizations actually try to combine components from multiple vendors in a storage area network (SAN), they quickly discover that the concept of open storage is still a myth.

In reality, widespread interoperability, even among standards-compliant products, doesn`t yet exist. The level of openness and interoperability varies depending on the vendor and the level of standards compliance and interoperability testing being done by that vendor. Invariably, some proprietary technology must be integrated to provide innovation or optimum performance.

With today`s SAN components, organizations are working with incomplete standards, imperfect standards implementations, and proprietary technologies. SANs consists of a collection of storage devices, including disk arrays and controllers, tape libraries and controllers, high-speed Fibre Channel subnetworks, hubs, switches, host bus adapters, and Fibre Channel-to-SCSI bridges. No single vendor makes every component of a SAN. To deliver a complete solution, vendors must forge interoperability among the disparate standards-compliant and proprietary components. Not every vendor is willing or able to do this.

Standards bring the goal of interoperability closer. Defined by the ANSI T-11 standards group, the Fibre Channel standard is already in its second iteration. However, as with any standard, ambiguities lead vendors to different interpretations. While standards are key to ensuring interoperability, even standards-compliant products may not work together.

But there is no standard for the SAN itself. The SAN is really an approach to storage that uses the Fibre Channel interconnect. The Fibre Channel standard defines only the interconnect, not the storage processes and operations that take place across the SAN. The standard does not address how the individual pieces of the SAN work with each other to handle storage processes. So, you can have interoperability, but still not have a multi-vendor SAN if the pieces haven`t been tested and certified.

In addition, the Fibre Channel standard is not nearly as ubiquitous as SCSI. Ultimately, Fibre Channel components will be as interoperable on the interconnect level as SCSI components are today, but for now the only assured interoperability is among components--standards-compliant and proprietary--that have been tested and certified to work together. Just complying with the Fibre Channel standard isn`t enough.

As part of the process of turning Fibre Channel into a ubiquitous standard, vendors are participating in "Plugfests." At these periodic gatherings, multiple vendors link their devices to a Fibre Channel loop to see what works and what doesn`t. But even these results are not conclusive proof of general openness or interoperability. Again, each component needs to be exhaustively tested to ensure complete compatibility and interoperability. While the Plugfests show progress toward interoperability and provide a fast way for vendors to identify problems, user organizations shouldn`t rely solely on these results.

The Storage Network Industry Associa- tion (SNIA) is also addressing SAN interoperability. For example, SNIA is attempting to define a common interface for network storage devices, which will make it easier to manage devices both on and off the SAN. When finished, this work will complete another piece of the SAN interoperability puzzle.

There are three key elements to achieving openness in SANs: 1) clearly written standards, 2) tightly defined profiles, and 3) rigorous testing and certification. However, in the end, testing and certification may prove to be the most important.

So, where does this leave managers who need to build SANs today? It will be some time before broad-based interoperability becomes a reality, but in the short term, organizations need to select vendor partners carefully, seeking those that actively support the Fibre Channel standard, define effective SAN profiles, and rigorously test components to ensure interoperability. By choosing these vendors, organizations can assemble a complete standards-compliant SAN that will work today and in the future as standards evolve.

Ultimately, managers need to balance their desire for broad openness--that is, the freedom to mix and match storage products--with certified interoperability. They also need to balance standards-compliant products with proprietary technology to ensure the optimum mix of interoperability, performance, and innovation. Interoperability can only be assured by working with vendors that support open standards and test and certify every component thoroughly.

Kirby Wadsworth is vice president of marketing in Compaq`s Storage Products Division (www.compaq.com), in Shrewsbury, MA.

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