Feature

Network appliance raises the bar for NAS/SAN convergence

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Data demands placed on businesses continue to grow and IT managers are responding by expanding storage, both in storage-attached networks (SAN) and network-attached storage (NAS) solutions. But this two tier approach, which balances performance, reliability and cost to suit specific missions, comes at a growing price. IT managers must manage two or more distinct and incompatible storage infrastructures, inviting spiraling costs and complexity.

Over the past 18 months, software and hardware vendors have released solutions aimed at closing the gapbetween block-based SANs and file-based NAS solutions. While none has bridged the SAN/NAS divide, the FAS900 series of converged devices from Network Appliance comes close. The FAS960 and FAS940 products offer in one box the file-based I/O functionality of NAS devices and the block-based I/O capability of SAN solutions. More importantly, the FAS900 series offers a unified environment, providing a common management console and dynamic allocation for both block- and file-based storage.

In effect, Network Appliance is promising seamless integration of both NAS and SAN storage. Network Appliance's motives are easy to understand: The Yankee Group estimates that at $7.44 billion, SAN revenues will triple NAS revenues this year and still more than double them in two years. The attraction for users, however, is a device that's more flexible, yet easier to manage, than a dual environment.

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Bringing file and block together

Bits are bits: At the disk level, the Network Appliance FAS960 and FAS940 don't care if data is being accessed via block- or file-level I/O. A unified storage scheme sits beneath the LUN and File Semantics abstraction layer.

"You can run blocks for those applications that absolutely require block I/O. And you can run file I/O as well and eliminate a whole bunch of servers," says Alan McLachlan, senior systems engineer for integrator ASI Solutions in Sydney, Australia. "Not only do you get more users per server. You can get rid of a whole bunch of servers."

But initial reports suggest that storage managers are not likely to adopt the Network Appliance approach to meet all of the demanding performance and reliability requirements of today's SANs. Rather, it will find favor for important parts of the storage infrastructure ill-served by current technology.

Courting convergence
Network Appliance isn't the first vendor to offer NAS and SAN connectivity in a single device. Products like the EMC Celerra, the IBM 300G, and NetApp's own F860 and F820 filers can connect to clients and servers via Ethernet on one side, and to a SAN-based disk array over Fibre Channel links on the other. These so-called NAS gateways, or NAS heads, allow IT managers to house all data-be it file- or block-based-on a single array of disks on the SAN. Consolidating disk storage around a single platform can help cut disk procurement costs and whittle down complexity.

The bits behind a NAS gateway may reside on a common physical platform, but still manage and access those bits distinctly. NAS-based storage occurs on specifically demarcated disks, with accesses traversing both the NAS device and the SAN. SAN accesses, meanwhile, bypass the NAS gateway entirely. Unfortunately, the additional layer adds complexity and introduces bottlenecks on the NAS side. More important, IT managers must employ distinct management consoles and tool sets to manage NAS and SAN-based data and resources.

The FAS900 series overcomes this by unifying the physical and logical storage environments in one device (see "Bringing file and block together"). As with NAS gateways, all storage resides on the SAN disk array. But where NAS gateways provide a portal for file-based I/O into the SAN array, the FAS900 series serves as the common access point to the array for both NAS and SAN operation. To do this, the device provides native block and file based I/O inside the device.

"One of the reasons I think this is an interesting system is because it allows the customer to take advantage of their infrastructure," says Mark Santora, vice president of marketing for Network Appliance. "They can move storage from IP to Fibre Channel at will. They don't have to copy and move data around. Just take that disk, move it over there, and boom."

This was first published in November 2002

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