Storage worlds converge

Organizations are of two minds when it comes to storage. One side of the brain — represented by engineers, software developers and scientists — desires the ease and flexibility of network-attached storage (NAS) appliances that can be hooked to the local-area network wherever more storage space is needed. This side wants to swap files and collaborate on projects.

The other side of the brain — featuring the information technology department — seeks the rationalized control of a storage-area network (SAN), in which multiple servers connect to multiple storage devices via a dedicated high-speed network. This side's main concern is giving servers access to the nitty-gritty block-level storage for business applications.

Can the hemispheres harmonize and reduce the burden on federal IT managers of having to manage two storage infrastructures? Yes, say industry executives who contend that the integration of NAS and SAN already is well under way, even as the differing demands that drove their development remain.

What Users Want

"The truth is, some applications require block access, i.e. SAN, and some applications require file access, i.e. NAS," said Peter Gerr, an analyst with Enterprise Storage Group, a market research firm in Milford, Mass.

"You've done the SAN and it works, but the end users don't get what they need," said Mark Amelang, director of marketing at NAS pioneer Auspex Systems Inc. "They don't use block-level data; they use file-level data."

Consequently, numerous vendors are rolling out products intended to unite NAS and SAN. Those vendors often use the phrase "NAS head" when describing their convergence strategies. The NAS head sits on top of block storage, stepping in to serve files to end users when needed. The integration promotes ease of management and satisfies the two methods of storage.

NAS is "an application or service that logically fits on top of a block device [and] will then give you the functionality of both block and file," Gerr said.

Auspex, Dell Computer Corp. and EMC Corp. are among the vendors pursing NAS and SAN coexistence. But some customers aren't ready for SAN, much less SAN/NAS integration. NAS vendors, however, argue that their products provide a migration path to SAN.

Coexistence with SAN speaks to NAS' maturation and acceptance in the enterprise storage space. A decade ago, NAS positioned itself on the edge of mainstream storage. Vendors such as Auspex and Network Appliance Inc. created devices that addressed the pain of user groups — an engineering department, for example — that needed a quick, easy and cost-effective way to share files.

Early NAS products were appliances that customers could readily plug in and use. As such, they tended to lack the robust fault-tolerance features and other characteristics of enterprise storage devices. NAS vendors, however, are addressing those issues.

"We're driving enterprise- class features lower and lower into the food chain on products," said Marc Padovani, product manager for Dell's PowerVault NAS line. Dell's midrange NAS servers, for example, include a backup utility and a "snapshot" tool that makes point-in-time copies of volume images.

Such features influenced the Army Aviation Technical Test Center's storage strategy. William Kodadek, IT project leader with Army contractor Cobro Corp., said fault tolerance — the ability to easily expand drive space and administrative features — provided an incentive to go with Dell's PowerVault solution.

In another move to bolster NAS, Auspex this year introduced a high-availability version of its NS3000 server. The NS3000XA consists of two NAS servers linked via Auspex ServerGuardV software.

Dual disk controllers and Fibre Channel host bus adapters in each server provide independent data paths to every disk array, according to Auspex. In addition, ServerGuardV, coupled with Auspex's operating system, provides additional protection, including "virtual network interfaces" that reroute network traffic if a Network Interface Card fails.

The National Weather Service's Aviation Weather Center has installed an NS3000XA to access data used in creating weather reports. Clinton Wallace, research and development meteorologist with the Aviation Weather Center, said the NAS server's redundant features have eliminated scheduled downtime. The center's forecasters can continue to access computer models, pilot reports and other weather data, even when half the server is down for maintenance or upgrades.

Gerr said NAS may not have achieved parity with SAN or block-storage devices, but contends that the technology has entered the storage mainstream. NAS, he said, "clearly is not a fringe product or a fringe application any longer."

Integration Tactics

NAS' maturity has set the technology on a course for integration with SAN. But an IT department's vision of managing an integrated storage pool also is driving attempts to bridge the technologies. Historically, scalability and management have not been among NAS' strong points.

"When SANs started to emerge, the pressure started to become much more dramatic on the need to scale," said Jeff Allen, senior vice president of strategy and business development at BlueArc Corp., a NAS vendor.

Traditional NAS appliances lack an "umbrella management schema," Gerr said. "Managing a large number of these devices tends to become unruly and inefficient."

Accordingly, IT departments face the contradiction of wanting to manage consolidated storage, while having to maintain numerous NAS servers. "People are saying, 'I want all storage consolidated — no renegade NAS users,' " Gerr said.

Numerous storage vendors offer an integrated SAN/NAS vision, but their actual contributions range from established products to statements of direction. As to the former, Gerr points to EMC's integration strategy for its Celerra NAS device as "very mature."

Indeed, EMC has been working on SAN/NAS integration since 1996. In the first phase of this development, EMC deployed Celerra to enable both NAS file system and block-oriented SAN access to coexist on the same EMC Symmetrix storage subsystem. And with the 2000 introduction of Celerra Highroad, EMC created a single file system for Symmetrix that distributes data through a SAN or NAS.

A large image file, for example, may efficiently traverse a Fibre Channel SAN, while a simple Web page request may be better handled through the general network side on IP, said Ken Steinhardt, director of technology analysis at EMC. The key is allowing "the nature of the application to determine the most appropriate path," he added.

Auspex's take on SAN/NAS linkage is somewhat different.

Amelang sees the company's recently introduced Network Storage Controller as the "next evolution of the NAS head." The Network Storage Controller employs NAS file-oriented protocols — rather than a complete NAS system — to access data from heterogeneous storage subsystems. According to Auspex, its controller will work with SAN storage subsystems from Hewlett-Packard Co., EMC, Hitachi Data Systems and LSI Logic Corp.

Not Ready For SAN?

Although SAN/NAS integration is feasible, some customers have no immediate plans to make that happen. "We had neither the money nor the in-house experience to immediately go to a SAN solution," Kodadek said of the Army test center. "A SAN is budgeted about two years out, especially if the need to access our data via SQL [Server] or Oracle Corp. [database systems] is required in the future."

But deferred integration is fine with vendors. "Now, we see customers that are interested in SANs, but not interested in a full SAN purchase," said Dell's Padovani. Now that Dell's NAS has Fibre Channel connectivity, a storage array can be migrated to a newly developed SAN and the NAS head plugged into the Fibre Channel switch, he said.

The role of NAS is shifting from inexpensive, independent storage appliance to SAN gateway. But vendors contend that the technology's traditional virtue of simplicity remains intact. "We can bring back simplicity of NAS into the SAN environment," Amelang said. "The value proposition is the same, but in a different paradigm."

And when federal customers are ready, they may find a storage solution for both sides of the organizational brain. n

Moore is a freelance writer based in Syracuse, N.Y.

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Storage terms

Network-attached storage — File-oriented storage device attached to a local-area network. Supports client applications via the Network File System and the Common Internet File System.

Storage-area network — Block-oriented storage network based on Fibre Channel; supports server applications.

Block — Basic unit in which data is stored and retrieved via disk or tape.

Fibre Channel — Standards for a serial input/output bus designed to transfer data between two ports, such as those on servers, switches and storage devices. Some current products achieve throughput speeds of up to 2 gigabits/sec.