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SAN deployment: Two views

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Experts Arun Taneja and Scott Robinson each offer valid ways of analyzing SAN consolidation.
Key determining factor Application requirements Service level (performance, high availability)
Server platform The platform doesn't matter with today's zoning and LUN masking capabilities, and multiplatform interoperability is no longer a problem Separate SANs by platform if you're not confident in your ability to use existing technology to manage multiple platforms on the same SAN
Organizational concerns Ideally, you want a single LAN, but organizational realities may require you to build separate LANs and bridge them Issues like budget and control may require you to build multiple SANs
Geography Long-distances will impact performance, so keep primary storage as close to the application as possible The cost of bandwidth and performance concerns will likely require the primary application storage be local
Security Zoning and LUN masking should be enough; use storage encryption where you need more security Separate SANs for security if you're not confident in your ability to isolate and protect SAN segments using SAN technology alone

Under the best of circumstances, he says, Factiva would have two SAN fabrics in each of its two data centers to ensure high availability. The company never considered running one pair of SAN fabrics across both data centers.

Companies that want to implement a single consolidated SAN need to consider the practical limits to current SAN scalability, such as performance and complexity. "You can't answer the size question easily," says Prigmore. Most SAN islands support about 10 servers. Although a few large SANs contain thousands of ports, those are rare. "IT will just have to decide where it wants to draw the line from a management and security perspective," he says.

BCBST doesn't see scalability as an issue. "We can support 100TB of storage with the full-time equivalent of one and a half people and could easily go to 200TB," says Venable, who has hundreds of servers attached to that SAN. The company--which is consolidating storage on a SAN consisting of seven IBM ESS storage arrays, McData fabric switches at the edge and two mirrored McData director-class switches--doesn't see a practical limit to how far it can scale its consolidated SAN. To manage the consolidated storage, it uses McData's SAN Navigator management software.

The bigger danger, in the view of the managers at BCBST, isn't scalability as much as starting too small. "We look at where we want to be in five years and start heading there now. We don't try to get there in lots of little steps," explains Hugh Hale, BCBST's director of technical services. The company's five-year plan was to get to consolidated enterprise storage sharing and get away from islands of storage. To date, the company has brought its 25 Unix and 250 Windows servers into the consolidated SAN. Soon, it will pull in the mainframe.

Ultimately, there's no simple answer to how large a SAN can or should grow. "The only thing I'd say is that the limit gets higher every year," says Hale. The size of any given SAN, ultimately, is constrained by any number of factors, ranging from available ports to bandwidth to management capabilities.

Much the same can be said about the question of whether to consolidate SANs or operate multiple SANs. Many factors will go into the answer. "Maybe we should consolidate our SANs eventually," says Petro-Canada's Black. But in the meantime, there are many organizations which have valid reasons for continuing to deploy multiple SANs, while others have equally valid reasons for consolidating them into one SAN. Do SANs taste great or are they less filling? You'll have to decide which is most important to you.

This was first published in August 2003

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