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SAN/NAS convergence: proceed with caution

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Until recently, technological and other barriers have kept the file and block storage worlds separate out on the network, with each in its own management domain and each with its own strengths and weaknesses. Many storage managers view block storage as the gold standard, with all of the bells and whistles, and view file storage a poor stepchild. Given the prevalence of business-critical databases housed on storage area networks (SANs), that's understandable.

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How hybrid systems work
In a converged environment, NAS gateways sit alongside block-savvy application servers to enable access to back-end SAN storage. But companies that opt for a multivendor solution often struggle to find a mix of products that will work well together.

Now, a slew of vendors are angling to improve large-scale file storage by drawing these two worlds together. Now that SANs are more common, the benefits of deploying network-attached storage (NAS) primarily as a file interface to the SAN are tantalizing. With a hybrid SAN-NAS solution, companies can consolidate block- and file-based data on common arrays. What's more, shifting NAS storage to an enterprise-class disk array can bring a host of benefits to file-based data operations, from sophisticated backup and snapshot capabilities to vastly improved scalability.

Yet issues remain. For example, some implementations raise concerns about performance and latency on SANs. Although growing weekly, product choices still aren't large. Picking the appropriate converged SAN-NAS solution is complex, says Phil Goodwin, senior program director for infrastructure strategies at the Stamford, CT-based Meta Group Inc.

The motive for convergence--constant storage growth--wasn't complex for Mike Forman at San Jose, CA-based Cadence Design Systems. As IT director of North American operations for the computer-aided design software provider, Forman oversees a global storage operation that includes half a dozen SANs across three continents. He also manages a fleet of nearly 50 NAS devices at remote offices worldwide. All told, Cadence manages approximately 300TB of data.

"We had hundreds of different file servers, and it was a nightmare keeping track of parts and dispatching [managers to service them]," says Forman, echoing a common complaint of storage managers faced with such environments. "And we were forecasting doubling storage every year, so it was only going to get worse."

Forman says the decision to converge file and block operations on back-end IBM Enterprise Storage Server (ESS) disk arrays arose from a strategic business need. As a developer of software, Cadence must provide enterprise-class file sharing for the hundreds of developers working on program code. With the company already supporting block-based I/O for its corporate Oracle database and Siebel CRM software, Cadence opted in 2001 to pull its proliferating file operations into the SAN. To do so, it deployed Sun Microsystems E420, E450 and E480 servers running Veritas ServPoint software at each of six corporate sites. The Veritas software allows the Sun servers to act as NAS gateways, also called NAS heads, onto the SAN.

"The SAN fabric is completely separate from the LAN. We do our backups on the SAN and we attach all our application servers to the SAN," says Forman. A cluster of NAS heads on each floor is the gateway for users to access the ESS arrays, typically across campus.

The move allowed Forman to consolidate direct-attached file storage and rein in spiraling management costs, but the solution is hardly perfect. Forman's team must use separate tools for configuring and managing block and file access. And Forman says he would like to find a SAN management tool that's more sophisticated than the IBM Specialist and IBM Expert software that his group uses today. But Forman is unequivocally satisfied: "The economics of a centralized solution are wonderful."

This was first published in September 2003

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