Network Attached Storage (NAS) has continued to evolve in the more than three years since our last guide. Your NAS budget today will generally buy a more powerful product with higher throughput and more features. But you might also find basic NAS needs satisfied by one of the many routers that now support USB storage sharing.
Let's first recap features all NASes support.
File Sharing - All NASes provide the basic function of networked storage—just like your computer does when you enable file sharing. But they use much less power, take up much less space and generate much less heat than desktop machines.
Client Backup - If you can read and write to a NAS, then a backup program can too. Some NASes come bundled with one or more backup utility licenses—usually for Windows machines. But if the NAS you're considering doesn't come bundled with a backup client, there are plenty to choose from.
Note that some bundled clients aren't very flexible or careful about how they load down your system when they run. So you might end up having to buy a backup program anyway. So don't let the presence or absence of a backup client affect your buy decision.
Many NASes also can be used as storage targets for Apple's Time Machine backup feature.
Ethernet Connection - All NASes also connect to a LAN via Ethernet. Gigabit Ethernet (10/100/1000) is now the rule vs. the exception and most NASes support Jumbo Frames. But lack of jumbo frame support isn't really a biggie. Today's network adapters and desktop OSes tend to move packets as fast if not faster without Jumbo Frames enabled.
If you're in the market for a high-end NAS, then you'll find 10GbE ports standard on some models, or supported via optional PCIe cards.
SMB / CIFS support - The lingua franca of networked filesystems is SMB / CIFS, which is supported by most modern OSes thanks to the work of the open source Samba project. This means any NAS will work with Windows, MacOS, Linux, etc.
The other main network file systems are NFS and AFP, which most NASes now support. Unless you're a 'nix user, you don't need to worry about NFS. You might want AFP support if your Macs are still using OS 9 or earlier. If the NAS you're considering supports Time Machine, then it supports AFP by definition.
Note that internal drive format used does not matter! Clients don't know or care how a NAS internally stores its data, whether it's EXT3/4, XFS or whatever. The only thing that matters to the client is the network file system / protocol. And here, SMB/CIFS is king.
Web browser-based administration - As with most consumer networking products, NASes are administrated through browser-based interfaces. Unlike today's routers, however, many NASes still rely on Windows or MacOS utilities to help you initially find the NAS IP address and change it to match your LAN's configuration. So if you have neither flavor of desktop or laptop on your LAN, be sure to check out the installation instructions for any prospective NAS purchase before you buy.
Fortunately, most NASes come set to automatically acquire their IP address settings via DHCP. So you can log into your LAN's router and find the NAS IP address in the DHCP client list. Overlook Soft's free Fing also comes in handy for finding all the devices on your network and displaying their IP addresses, services and more.
Expansion via USB - It's rare to find a NAS that doesn't have one or more USB ports. Among other functions, these ports can be used to connect USB storage, which can be used to back up NAS internal storage or be shared on the network. As USB 3.0 has become more common, eSATA ports have become less important for getting high throughput from attached drives and are generally found only on more expensive models.
Multiple User Accounts - With few exceptions, all NASes let you create multiple users and assign password protected storage space for them. You can also set up "Public" folders that all users can access without a password.
NOTE! Just because you can set up Users doesn't always mean you can set up Groups. If you need this feature, be sure to check the NAS specs and features carefully.
Diskful or B.Y.O.D.
A key decision for narrowing your selection field is whether to buy a NAS that comes with hard drive(s) installed (diskful) or without (Bring Your Own Drive).
Diskful NASes generally cost less than BYOD models when equipped with equivalent storage, especially single-drive models. The main downside for diskful is when the internal hard drive dies, replacement is usually a factory-only option. One year warranties might tip your decision toward BYOD models. But three year warranties might make it a diskful model worth it, especiall if you like to upgrade often to stay current.
Bring Your Own Drive (BYOD) NASes' key advantage over diskful models is easy drive replacement, because they must have the ability to format and install whatever files are needed on any raw drive. Many multi-drive RAID NASes also let you start with a single drive and then add more drives as your storage needs grow.
But download the user manual of any prospective buy and read through the details of its RAID migration and expansion features before buying. Manual RAID migration isn't usually supported among all volume configurations. RAID expansion also is very time consuming and requires a volume resync after each drive is replaced. A four-drive RAID 5 expansion can easily take over a day using 1 TB drives. And unless you're dealing with a RAID 6 volume, every second an array is resyncing leaves you open to losing all your data.
Many RAID 5, i.e. four-bay and higher, models support some sort of automatic RAID migration / expansion system that automatically expands volume capacity as drives are added. Synology's SHR and NETGEAR's automatic RAID are two examples of this feature.
Finally, you can't necessarily throw those old drives you have sitting on a shelf into your new NAS. For best performance and reliability, you should stick to drives chosen from a product's supported drive list. See Is That an Approved Drive In Your NAS? Or Are You Happy To Risk Your Data?