Much more than an external hard drive, the latest NAS devices have transformed themselves into full-featured, multi-purpose computing devices that can act as media, print, and file servers; surveillance devices; web hosts; and even file-streaming servers for mobile phones. Indeed, the term "network attached storage" is probably a misnomer. The new NAS, with its own chipset, operating system, and network connectivity options, is essentially a "network attached server."
In fact, if you have a spare PC with a CD-ROM and hard drive that you'd like to press into service as a NAS, you can set it up with FreeNAS, a FreeBSD Unix-based distribution that supports the most common NAS protocols, server processes, and applications. But considering the low cost, quality assurance, and bundled capabilities of the commercial alternatives, it's probably worthwhile to spend your time figuring out which off-the-shelf hardware is best for your needs instead of experimenting with the build-your-own approach.
NAS devices can be evaluated on several dimensions, including storage, PC backup, NAS backup, and server-based applications.
How Much Storage Do You Need?
Unlike an ordinary external hard drive connected directly to a PC, network attached storage can be shared across a network by multiple users using multiple devices. Although NAS devices typically have an upper limit to user accounts, groups, and concurrent users, these limits are usually set rather high -- in the hundreds or even thousands -- befitting the origins of NAS as an enterprise and workgroup technology. The real limitation is available disk space.
For each computer you own, you should plan to perform incremental file backups, including a full system image of your operating system, programs, settings, and files. That way, if the PC hard drive fails, you can simply get a new one and restore from the image. To estimate the size requirements, add the size of your documents folder to the total hard drive space used for each of your systems, and multiply by a factor of three or four.
Next, estimate your rate of data growth. One terabyte of storage, or 1,024 gigabytes, holds about 680 movies downloaded from the iTunes Store. So, if your family downloads three movies per week, it would take you about four years to fill a single terabyte. But if you're also adding other file downloads, or if someone at home is engaged with music composition, video production, 3-D graphics, or other storage-intensive applications, you'll need to plan accordingly with a larger target for disk space.
Give yourself plenty of room: One terabyte sounds like a lot of space, but so did 80 gigabytes just five years ago.