Where can you turn? It's NAS to the rescue. You can effectively use NAS devices to shore up or replace existing storage systems in your enterprise.
NAS and SAN, Yin and Yang
The terms we use for storage systems befuddle many. NAS stands for network-attached storage; SAN, storage-area network. The difference between the two is a matter of perspective. NAS devices are appliances with easy-to-use interfaces atop a prepackaged OS--a plug-and-play appliance for storage, some might say. The primary purpose of a NAS device is to offer storage shares on the network to other machines. How does a server with a RAID array and some shares to offer differ? At the physical level, there is no difference. A NAS device is a packaged server specifically designed for storage. The real difference is in terms of ease of use, price and other convenience features.
A SAN is traditionally a Fibre Channel network, with switches and storage attached to file servers and set up to maximize speed and reliability. Can a NAS be a part of a SAN? Absolutely. Some NAS devices use Fibre Channel and can be connected directly to a Fibre Channel switch. NAS heads interface with your Fibre Channel SAN. Confused? You won't be for long. In the future, new protocols and increased Ethernet speeds may make the differences moot. If iSCSI and other storage-over-IP protocols get through the standards process (and they should), the difference between your storage network and your data network will be a matter of semantics and segmentation.
Today, though, you have a real--and usually easy--choice between NAS and SAN. The choice is not which horse to back, but which one will run better for your application. If you need very high-speed transfers with huge amounts of data or plan to move many multiples of terabytes or petabytes, you need a Fibre Channel SAN, because NAS is inherently limited to the speed of Ethernet. If your storage speed and size requirements are less, but you want good management, a NAS device probably will do the trick.
To make the decision, know the traffic load on your infrastructure and make sure your existing Ethernet infrastructure can handle it. Also, make sure the task you assign your NAS device is appropriate based on your data-rate needs. NAS devices can offer data to a server or workstation only as fast as the Ethernet network allows. In many cases, this is acceptable, but particularly sensitive processes may need a more direct form of storage access, such as Fibre Channel or SCSI. The people, programs and processes that can benefit from a NAS implementation have increased dramatically with the advent of Gigabit Ethernet. Just make sure you're purchasing the correct speed for your NAS device, because you'll get only one chance. Another excellent place for NAS devices is on your Web infrastructure, because these environments already are limited to IP and Ethernet bandwidth.
How To Spot a NAS
The hallmarks of a NAS device are ease of use, ease of installation, remote management and security. When purchasing a NAS device, keep convenience features high on your list. A NAS device that takes longer to set up than a server with storage is useless. Because NAS devices are appliances, the setup should go something like this: Plug in. Boot. Minimally configure. Walk away. If excessive time is spent on the front end or on continued maintenance, the device, no matter how inexpensive, is not a good buy.
Additionally, if you can get a NAS device that integrates, or at least interfaces, with your current file-security scheme, you'll save time on the setup and with ongoing maintenance. All NAS devices are remotely manageable, apart from initial setup, and on many units the initial setup is needed only for network settings. From there, configuration and management are performed via a browser or a provided management application.
A decent price-per-MB ratio is a good indicator of a NAS device's usefulness. When calculating the alternatives to NAS, include the price of the server machine and the OS to drive it--not just the storage. Also take into account the connectivity piece. Then figure in your time to set up the server. All four factors must be calculated, yet many people neglect one or more when buying NAS devices.
I've heard many argue, "We have an old Compaq server that we just retired laying around; it'll do fine as a head end for additional storage." Although we don't doubt that it would, that solution has a few problems. How reliable is the ancient RAID system in that old server? What kind of network connections does it have? Do you have a license for an OS to install on it? With the changes that Microsoft is making to its license schemes, that becomes a very important question. Do you have a network administrator with enough free time on his or her hands to dedicate a day to setting it up and getting it running? Will you put money into an old machine if it breaks? Answer all these questions before you dismiss the idea of a NAS device.
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