How to choose a NAS

When Benjamin Franklin said "In this world nothing is certain but death and taxes" he could have added running out of disk space and hard drive crashes. Thankfully, although we're stuck with death and taxes, there is a way through the problem of storage.

Network Attached Storage, or NAS, has moved from the enterprise to the SME and home. It's now possible to buy a decent NAS for under $1000 including disks. But what do you look for?

Capacity

In simple terms, the more drives you can cram into a NAS the greater its potential storage capacity. In most cases, we suggest something with four or five bays like the Synonology DS-1511. Loaded up with a swag of 1TB or 2TB drives it offers plenty of capacity.

If your needs are more modest then a two-bay unit is also handy and won't eat into the budget.

RAID levels

As most NAS units come with more than one hard disk (it's possible to buy a device with a single disk that;s shared over a network) you need a way to get those drives to work together. The way those two or more hard disks work together is described through a standard called RAID, or a Redundant Array of Inexpensive Disks.

Where a NAS device has two hard disks, the disks can either be configured to mirror each other, RAID1, or to look like a single, large hard disk, RAID0.

RAID0 offers improved performance but it comes at a cost. If either one of the two disks fails then all the data, spread over both disks is lost. Two 500GB hard drives in a RAID0 configuration will deliver about 1TB of available storage.

In a RAID1 configuration, two 500GB drives will provide a total of 500GB of storage. That's because all the data is automatically written to both drives at the same time. There's a performance hit but the result is that if one disk fails, you shouldn't lose any data. It's worth remembering that there are two types of hard disk - those that have failed and those that will fail.

With arrays of three or more disks, RAID5 comes into play. In a RAID5 array, the data is written to more than one disk but it's done in such a way so that if one disk fails you won't lose any data. In other words, it's a bit of a cross between RAID0 and RAID1. RAID5 offers both performance improvements and hardware redundancy. A RAID5 array of four 1TB hard drives will deliver about 3TB of available storage.

RAID6 is similar to RAID5 but allows for two disks to be lost without any data loss. RAID10 is a hybrid RAID level that works like both RAID 1 and 0 together. Essentially, two RAID0 arrays are configured so that the data is written to both arrays at the same time.

There are several other RAID levels but these options are the most common and will serve the needs of the vast majority of people.

Choosing disks

Many NAS makers allow you to choose between buying a ready-to-go unit that's loaded up with some drives or sell you an empty chassis. We'd suggest buying the empty chassis so that you can choose your preferred drives. Just one thing - not all drives are deemed compatible with all NAS devices. Most manufacturers maintain a compatibility list (such as this one for the Dlink DNS-1200-05).

One thing to be especially careful about is that many NAS devices won;t play well with "green" drives that automatically power down in event on inactivity. Some NAS will see this as a disk failure so check carefully before committing to your drive purchase.

Features

The features you'll want will depend on what you're planning to use the NAS for. If you're running a multi-platform office then make sure that your chosen NAS can share files over the right protocols. If the intent is to make your NAS accessible from outside the LAN then Secure FTP might be worth considering.

Given that most homes seem to have an iPad, iPhone of iPod touch it may be worth ensuring that your NAS can support WebDAV as a file sharing protocol. so that your iOS devices can access and share data. A number of QNAP NAS devices support WebDAV .

One of the most common applications for a NAS is as media server. Many devices mow natively support iTunes sharing as well as UPnP and other media sharing systems such as Twonky Media Server.

There are also download managers, backup systems and lots of other applications that can come as part of a NAS. It's worth thinking about all the potential "bonus" features you NAS might offer.