On the recommendation of a colleague I recently picked up a QNAP TS-451 NAS for my home office. NAS stands for Network Attached Storage, which is a fancy way of saying "file server".
Wikipedia offers this definition:
A NAS unit is a computer connected to a network that provides only file-based data storage services to other devices on the network. Although it may technically be possible to run other software on a NAS unit, it is not designed to be a general purpose server. For example, NAS units usually do not have a keyboard or display, and are controlled and configured over the network, often using a browser.
I quibble with this definition, because the TS-451, like a lot of NAS boxes out there, does much more than just serve files. But file storage really is the starting point.
Why a NAS?
But why would you want a NAS in the first place, especially for a home or small business office? If it's just extra storage, isn't it easier to throw a big cheap drive into an existing PC and create a network share?
In my experience so far, the value of a NAS falls into two categories: data redundancy and server applications.
Data redundancy
Although QNAP sells a single-drive NAS, I think it's silly not to take advantage of data redundancy in a NAS. The TS-451 has four hot-swappable drive bays, although at a minimum you only need to use one of those bays. Supported RAID modes (for all QNAP models except those with one bay) include RAID 1, 5, 6 and 10.
I had some existing drives I could use, so at present I have three 2TB drives installed in a RAID 5 configuration. If one drive fails I can pull that drive from the enclosure while the NAS is running, replace it with another drive, and the NAS will rebuild the drive array without data loss. That's because . That isn't a quick process - I would expect it take somewhere around a day with the size of drives I currently have.
Data redundancy comes at a cost; although I have 6 TB of disk space across three drives, I only have 4 TB available for use. (I guess I'm getting old - I still find it quite bizarre to use the words "only" and "terabyte" in the same phrase.)
Although all three of my drives are 2 TB, that doesn't need to be the case. The next drive I add will probably be 4 TB. That will only increase my total capacity from 4 TB to 6 TB, but once I've upgraded the other drives to 4TB I'll be able to expand my RAID capacity to a total of 12 TB.
It's also possible to start with a single drive and then migrate it to a RAID configuration. See the QNAP docs on RAID expansion and migration for more information.
Is RAID 5 good enough?
There's been a certain amount of press about the risks of using RAID 5 in small arrays, like that offered by the TS-451. The concern is that if a single drive fails, and there's a unrecoverable read error during the rebuild of the new drive, the rebuild could fail and you will lose all the data. The recommendation then is to go RAID 6 (double parity) or RAID 10 (striping + parity) both of which require at least four drives and which have an availability of 50% of the total drive space. (For a calculation of how much space you can use with various configurations see this RAID calculator.)
I've done some reading on this and have decided for now to stick with RAID 5. I think the main thing to take away from the discussion is that no matter what RAID configuration you use, RAID is about maintaining access to data in the event of a single drive failure; it is absolutely not a replacement for offsite backups. You still need to be prepared to deal with catastrophic failure.