Sane strategies for SAN growth


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Merrill Lynch's three-year refresh
Larger shops plan for a complete storage area network (SAN) technology refresh every three or four years, typically the length of the lease arrangement with their existing vendors.

"All designs are short-lived, right?" says Max Riggsbee, an independent storage consultant working with Merrill Lynch & Co. Inc. in New York. "At the end of three years, there's new technology to consider and we're likely to change out different elements of the SAN."

Merrill's SAN currently supports approximately 300 hosts, with a design maximum of 500 hosts and around 1,000 host bus adapters (HBAs). "If we get up to the limit, we can add more edge switches," Riggsbee says. "But at some point, we'll hit the port density of the switches."

The SAN is based on a three-tier design that uses 122 Brocade 12000 switches, says Jerry Curtis, business manager of data management and distributed services at Merrill Lynch. "We have a single dual-path SAN fabric that allows all systems to see all the storage devices," he explains. The company's storage includes approximately 240TB of EMC storage and another 100TB in Hitachi boxes.

Although the firm "probably uses more ports for inter-switch links (ISLs) than a traditional two-tier SAN island design," Curtis says it's worth it. The costs are offset by their high utilization of storage assets and the flexibility of managing and changing the existing storage configuration. "We have around seven people managing 340 terabytes of the storage," he says. "We made decisions about SAN islands vs. three-tier, and the costs are pretty minor in comparison." Also, he says, with a traditional two-tier design, "you can have problems getting to the storage devices."

On the utilization side, "most of our arrays run around 95%," Curtis says, in large part because provisioning software is designed and written in-house. Storage administrators schedule the provisioning after stock exchange hours, and the software makes whatever zoning changes are needed to the fabric. Merrill Lynch is currently negotiating with commercial software vendors to take over the development and support of that provisioning system because "I'd rather have someone else doing the testing and point releases," Curtis says. "It's not part of our core competency."

The firm recently installed an application subscription system that changes the way that Merrill Lynch bills out storage (and all IT resources) to end-user departments. Now Curtis can tell users exactly what he's going to charge them every year for various applications. Every application now subscribes to resources in the data center, and "we have sponsors behind the applications. And we've become Amazon.com--we order it, track it and can change various line items. The result has been very tight management of our resources," he says.

When the company hits the end of the expansion road for its current SAN design, Riggsbee says, he'll be looking at technologies that allow for multipath access from his applications to different levels of storage. This will provide more redundancy, and will allow access to different types of nearline and online storage for backup. Ideally, he says, any new intelligent fabric and switches will provide for synchronous and asynchronous backup at the same time.

"We're seeing some talk in the SAN space about products moving into the fabric, and that's a great thing," Curtis says. One example, he says, would be the types of functions provided by Veritas' Volume Manager--configuring, sharing, managing and optimizing storage I/O performance without interrupting data availability. Curtis' major goals with this more fabric-based approach would be to make storage functions "easier to implement" and to more effectively use network bandwidth, he says.

Curtis wishes he could plug a server into a fabric with the same ease as plugging a PC into a network. "When you do that," he says, "you never have to worry about compatibility issues between the PC and the network ... until it gets much easier, companies will be cautious about committing to a SAN-attached environment because of the labor costs and complexity."

In the meantime, Merrill is beginning its annual storage review, something the company was starting as this story went to press. "We go through the assumptions and policies we have for the current year, and decide if they still hold true for the coming year," Curtis says. They apply what they know about their end-users' upcoming projects and other needs, as well as technology roadmaps from vendors to determine how their SAN will expand.

--By Johanna Ambrosio

This was first published in November 2003

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