One of the basic choices you need to make when buying a NAS is whether you want one with (diskful) or without (diskless or Bring Your Own Drive) drives. Here are four things to consider when making your choice.
1. When A Drive Fails
When the drive fails in a NAS (and all drives do die eventually), owners of BYOD NASes usually have an easier time replacing the drive. This type of NAS provides easy physical access to the drives and must be able to initialize drives that are installed.
With diskful NASes, replacement is usually a factory-only option. Diskful NASes, single-drive versions especially, usually aren't designed to allow users to easily open the case to replace the drive. And even if the drive is easy to get at, diskful NASes can't initialize the new drive on their own.
But consider warranty length before you automatically choose a BYOD NAS. If your diskful NAS comes with a three-year warranty and a low price, it could well be worth it. Three years is almost forever in the NAS world, and you may want more space and faster transfer speeds even before your warranty expires!
Bringing either flavor of NAS back to life after a disk failure will be a lot easier if you have a backup of the NAS contents, or at least a backup of anything you can't afford to lose. As noted in Smart SOHOs Don't Do RAID, RAID is not a substitute for backup.
There are many ways that a RAID volume can fail, some of which make it difficult, if not impossible to recover. It doesn't matter if the failure is due to poor design, cockpit error or phase of the moon. You have no one but yourself to blame if you rely on RAID as your backup.
Keep in mind, also, that while your NAS is rebuilding the RAID volume after you replace a failed drive, if something goes wrong during the rebuild, the volume is usually gone. Rebuilds of multi-Terabyte volumes can easily take 8+ hours, and more if the volume is in use during rebuild. Your rebuild will go a lot faster and with less chance of failure if you can switch over to a backup NAS
2. Storage Expansion
If you are considering a start-small-and-grow approach, you should download the user manual of any prospective purchase and read through the details of its RAID migration and expansion features. RAID migration usually isn't 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. This is another reason for having a full backup of your NAS. It's a lot safer and faster to just build a fresh new volume than to expand a current one.
But slow transfer speeds for copying data back to the fresh new volume could take almost as much time as using the volume expansion method. The fastest way will usually be via direct NAS to NAS copy, usually using some form of rsync instead of using a computer to drag and drop folders between NASes.
You also can't necessarily throw those old drives that 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?
It seems counter-intuitive, but diskful NASes are generally cheaper than BYOD. The main reason for this is that BYOD NASes tend to be more fully-featured than their diskful counterparts. And with premium features come premium prices.
NAS manufacturers can also negotiate lower costs for the volumes of drives they buy than what you'll pay at retail.
One way to offset the higher price of diskless NASes is to look for deals on previous-generation products. Many manufacturers (QNAP, Synology, NETGEAR) now support the same feature set across their product lines. So you don't necessarily have to buy a honkin' big eight-bay octal-core speed demon to get the features you want. If you're willing to accept lower performance and don't overestimate your need for storage expansion, you may be able to go BYOD and not pay a premium.
4. Removable Drives Might Not Mean BYOD
Just because a product has removable drives, doesn't necessarily mean that you can treat it as a BYOD NAS. Buffalo, in particular, does not support users populating Buffalo NASes with their own drives. Although there are how-tos describing how to get Buffalo NASes running using all new drives, the process voids warranty and Buffalo will offer little support help.
The easiest way to know if a diskful product also supports BYOD mode is to look for a diskless configuration of the product. NETGEAR offers many of its ReadyNASes in both diskful and diskless models, for example.