When it's a Storage Server.

Ask people what a storage server is, and you can expect to hear a variety of answers. Some will say it is a regular server with added features, a few describe it as a stripped-down box dedicated to a specialized function, and still others believe the term refers only to a network attached storage (NAS) box.

This article will attempt to define a storage server, differentiate it from a regular server, and give examples of storage servers on the market.

The typical server is configured to perform multiple functions. It operates as a file, print, application database, Web, or miscellaneous server. As such, it must have fast chips, more RAM, and plenty of internal disk space to cope with whatever end users decide to do with it.

Not so with a storage server. It is designed for a specific purpose, and thus configured differently. It may come with a little extra storage or a great deal.

"A general-purpose server typically has five or less disks inside," says Graham Lovell, senior director x64 servers at Sun Microsystems. "A storage server, on the other hand, has at least six, and more, usually 12 to 24 disks."

Storage servers are normally individual units. Sometimes they are built into a 4U rackmount. Alternatively, they can consist of two boxes — a storage unit and a server located near by. Both boxes can then be placed side-by-side in a rack. The Sun StorEdge 3120 storage unit and SunFire X4100 server, for example, can be combined into a storage server and placed in a rack.

Apart from extra disks, what else is different about storage servers? In many cases, they come with a host of specialized services. This can include storage management software, extra hardware for higher resilience, a range of RAID configurations and extra network connections to enable more users to be desktops to be connected to it.

Interestingly, some vendors define storage servers purely in terms of NAS. A NAS appliance (also known as a NAS filer) generally has a slimmed-down OS and file system, and only processes I/O requests by the main file sharing protocols. The big advantage of the NAS architecture is that it enables storage to be rapidly added by plugging the appliance into a network hub or switch.

"As far as HP is concerned, a storage server is NAS," says Jim Hankins, product marketing manager for HP's NAS division. "In essence, it is a dedicated file and print server."

HP has five ProLiant models available as general-purpose servers or storage servers/NAS filer — each has the same basic hardware configuration. If licensed as a storage server, the user may not run general-purpose applications on that server. If the same ProLiant server is being used as a regular server, however, applications can be run on it. To sweeten the deal, HP prices its storage servers a little lower than their general-purpose siblings.

In addition, HP's NAS-based storage servers have extra functionality built into the operating system — storage-specific management tools, "quota-ing" features, storage reporting capabilities, and a Web-based user interface that makes it easier to configure file and print. These features are not available on its general-purpose servers.

"For a little bit less, you get a lot more value add," says Hankins.

So is NAS really just a storage server? The answer varies, depending on whom you ask. But it appears there is very little difference between them. NAS, it turns out, isn't really storage networking. Actual network-attached storage would be storage attached to a storage-area network (SAN). NAS, on the other hand, is just a specialized server attached to a local-area network. All it does is make its files available to users and applications connected to that NAS box — much the same as a storage server.

"NAS is a marketing term," says Dan Tanner, an analyst at storage consulting firm ProgresSmart. "NAS is really nothing more than a file server, but specialized or adapted to the single purpose of serving files."

And what a marketing campaign it has been. From nowhere in the mid-1990s, Gartner projections predict the NAS market will exceed $2 billion by 2008, with an annual growth rate of 9 percent. And those numbers don't take into account a new NAS flavor called the NAS gateway. These gateways act as a file serving portal into a SAN: There are disk arrays in a Fibre Channel SAN that have a storage server on the perimeter acting as a NAS gateway. This is a one way to marry up NAS and SAN assets.

"There are two flavors of storage servers," says Hankins, "NAS appliances that have the disk storage in the appliance, and NAS gateways."

The ProLiant DL585 storage server is one example of a HP NAS gateway.

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