While some vendors use the same box as a plain vanilla server, others use a scaled-down version that is adequate for file serving. This is explained by Steve Duplessie, senior analyst at Enterprise Strategy Group. He defines a storage server as an optimized appliance designed to feed information, via a network, to a user or an application. As such, it is not typically compute heavy, but it has been designed from the ground up to provide specific I/O capabilities along with data protection capabilities.
“A regular server has to be generic, it doesn’t know what kind of load demands it will have — gaming is much different than running a database, for example. A storage server, such as a NAS box, is a contained appliance that does one thing really well, like file serving.
What does a “regular” server have that a storage server doesn’t? According to Duplessie, it typically has more processing power, more RAM, and a more generic I/O structure and file system. As a result, most storage servers perform at 50 percent of the performance of a regular server for the same function, he says.
What does a “regular” server have that a storage server doesn’t — More processing power, more RAM, and a more generic I/O structure and file system.
This trend toward specialized computing elements is far from new. TCP/IP routing, for example, was a function that every operating system ran — until Cisco came out with a dedicated box that did it far better than hosting it on a general-purpose server.
“Any time you can optimize a function, it will be better [on a specialized box] than if executed on general-purpose gear,” says Duplessie.
Dan Tanner, an analyst with the storage consulting firm ProgresSmart, agrees with Duplessie’s view that a storage server is a specialized server or appliance.
“The server OS is cut down to address purely print server or file server functions, and often contains specially tuned or enhanced code,” says Tanner. “Before NAS came along, though, Microsoft said you could use a regular server for file serving.”
But using a vanilla server for file serving could lead to problems. Administering a general-purpose server is more complex. Further, someone might be tempted to use the server for multiple functions. Dedicated storage servers, therefore, have become the norm.
Not surprisingly, Microsoft introduced Windows Storage Server 2003 to distinguish it from general servers running the Windows 200x operating system. Windows Storage Server 2003 is a dedicated file and print server based on Windows Server 2003 and tailored to networked storage. It supports file serving and backup and replication of stored data. It can also be used to consolidate multiple file servers into a single box.
Windows Storage Server 2003 includes advanced availability features, such as point-in-time data copies, replication, and server clustering. They come in sizes ranging from a few hundred gigabytes to several terabytes. It is available in pre-configured NAS appliances from vendors such as HP and Dell. As a result, IDC reports NAS appliances running Windows now account for about half of all appliances in the market.
Storage Servers vs. Disk Arrays
Just as there is some confusion between ordinary servers and storage servers, there is also sometimes a misunderstanding between storage servers and disk arrays. Exactly where does one end and the other begin? A storage server can have as many as 24 disks — enough to quality as an array. Disk arrays, however, can have hundreds of disks. So where do you draw the line?
“A storage server is usually stand-alone and not connected to other servers,” says Lovell. “Multiple servers, however, typically connect to a disk array.”
Disk arrays, too, often connect to a server that could be styled a storage server. The storage server is the intelligence that goes in front of the array. In this arrangement, the server can manage several tiers of storage. It can even arrange the replication of data from one tier to another.
“A storage server serves the storage, and the disk array is the storage,” says Tanner. “Using a storage server lets you use multiple or different arrays.”
Duplessie further separates the two terms.
“A storage server typically speaks to files and talks to people or applications over Ethernet,” says Duplessie. “A disk array is a low-level block device that only speaks to an operating system.”
Vendors Offering Storage Servers
There are plenty of storage servers on the market. Here is a sampling of what’s out there:
|Sun||Sun StorEdge 5210 NAS and Sun StorEdge 5310 NAS|
|HP||HP has six storage servers available, including the ProLiant DL100 G2 storage server|
|Dell||PowerVault 745N qualifies as a storage server|
|Network Appliance||Offers a range of NAS products, including the FAS200 Series|
|Aberdeen, Inc.||several storage servers|
|Microsoft||Microsoft Storage Server 2003|