2 Bay vs 4 Bay NAS – Which is Best?
2 bays, or 4? Seems like a simple choice right, but there’s a few things you should know and might want to consider before picking one up. A quick refresher on what a NAS is for anyone who isn’t sure, a NAS is a network attached storage device. Basically it’s a computer with storage drives in it that you access over your local area network or LAN, rather than direct attach storage devices like a USB hard drive. In general, you want at least 2 drives in that NAS in what’s called RAID 1.
RAID stands for redundant array of inexpensive disks, and RAID 1 means the data you write to one drive gets 1:1 copied to the other so if one drive fails the data is stored on the other. That does mean you need identical drives and that you will only be able to use the capacity of one drive since the other is just duplicating the data. There are other types of RAID you could run here, including RAID 0, but I said ‘could’ for a good reason. Running RAID 0 on a NAS is a terrible, awful, horrific idea. The reason for that is RAID 0 ‘stripes’ your data, basically it splits it in half and writes half to one drive and the other half to your other drive. It gives you faster performance and lets you use the full capacity of both of your drives, but if either drive gives up the ghost you’ve lost ALL your data.
The other kinds of RAID all require more than 2 drives which is where these 4 bay units come in. RAID 5 for example requires at least 3 disks but instead of storing a copy of the data itself it stores what’s called a parity block, basically check, a signature, that means if a drive were to fail you can do some maths with the remaining data and the parity block and re-create the lost data. That means one drive can fail and you won’t lose any data, and you get the benefit of only losing one drive’s worth of storage space, so 4 10TB drives in this NAS would give you 30TB of usable space in RAID 5 whereas RAID 1 would only give you 20TB of usable space.
RAID 6 is the same as RAID 5, but stores 2 parity blocks instead of just 1. That means you can sustain 2 drive failures and lose no data, at the cost of losing 2 disks worth of capacity which in this 4 bay enclosure would be the same as RAID 1. Also, both RAID 5 and 6 both ‘stripe’ the data, meaning it writes to all drives simultaneously so you get faster performance. There is also RAID 10, which is what’s called a “Nested RAID”, as it takes the 4 drives in here and makes two groups of RAID 0, then uses RAID 1 to mirror the data on the first two drives to the second two. In theory this is better than RAID 5 or 6 as while you do lose 2 drives worth of space and a bit slower performance, if a drive fails it will only read from two of the disks rather than all three to rebuild the array rather than the more read intensive process RAID 5 or 6 need.
All of these fancier options are only going to be available to 4 Bay NAS users, as well as the obvious capacity increase both from being able to use say RAID 5 instead of RAID 1, but also just have two more physical bays to put drives in. While this likely isn’t a massive problem especially with 16TB and 18TB drives on the market it can even be useful as a futureproofing point as with a 4 bay NAS you could buy 3 drives now and set it up in RAID 5, then in a few years when you want more space, buy another of the same drive and add it to your array. Rather obviously, that’s not possible on the 2 bay unit.
The 4 bay also offers more flexibility, for example many units support SSD caching meaning you can have your 3 drives in RAID 5, and the fourth bay has a 2.5” SATA SSD that acts like a reservoir for your files. It can store your data much faster than your hard disks can, then slowly write the new data to the array in it’s own time. You can even set them up as a read cache too, where frequently accessed files will have a copy stored on the SSD so you can read them much faster than the disks spinning and mechanical arms moving around to find your data.
The main advantage of the 2 bay units is price. You are buying a physically smaller device with less drive bays, so it’s pretty much always going to be cheaper than it’s 4 bay equivalent. Occasionally the 2 bay unit might also be a lower spec, like offering less RAM or a slower processor, but if you are willing to spend 4 bay NAS money on a 2 bay unit you can get much better specs and sometimes even more features too.
I’ve had a few 2 bay NAS units which featured PCIe slots at the top, and supported add-in cards like the QNAP QM2 which not only added 10G ethernet support, but also 2 M.2 SSD slots for ultra-fast SSD caching. Those 2 bay units cost around the same as this more budget 4 bay model, and yet offer more (and upgradable) RAM, a much faster CPU and a PCIe slot for further expansion.
I want to quickly note a few extra feature differences or things to consider when buying a NAS like these. First is what speed the ethernet runs at, the standard is generally 1G, which is more than likely what your home network is based on, but you can get 2.5G like both of these, and even 5G and 10G on some fairly high end models. You will need a switch or router that can run at those speeds, and ideally devices to run that fast too, but if you want to say work off of your NAS like I do, higher is better here.
You can also keep an eye out for extra features, like the PCIe slots, but also for upgradable RAM, more USB ports and physical copy or clone buttons to instantly backup USB drives, displays on the unit to show you status messages, display outputs to let your NAS act like a smart TV device (think Roku or Chromecast) or other storage features like built-in M.2 slots for SSD caching while not taking up any drive bays.
So, who should buy a 2 bay NAS? As a sweeping generalisation, anyone looking for a simple, easy home backup solution for their family photos, documents and videos. If you want to host your own bluray collection and be able to stream them with a tool like Plex, these are great for that. If you are a bit more of a power user you can get a fancier model with more features, but the storage cap here is generally either 16TB or 18TB depending on the model, and assuming you aren’t willing to risk losing all your data in a heartbeat with RAID 0.
What about a 4 bay? Again, in general, anyone who needs more than 16/18TB of storage space, needs better security or write speeds to their data or wants a SATA SSD cache. If you work from home or are self employed and have lots of things to store and maybe even run from your NAS like web servers, media servers or collaboration tools, a 4 bay unit might be a better bet. While you will be spending more to get the same sorts of features, especially if it’s a business expense it’s well worth the cost.
It’s worth noting that there are other options, both as enclosures like these and building one yourself like my Overkill NAS project. Enclosures don’t just come as 2 or 4 bay sizes, you can get anything from 1 bay (which I personally don’t recommend) to 9 bays, and of course even more if you want to buy a rackmount server instead. DIYing it is also a good option if you are more of a power user, or you have an old PC lying around that you want to make use of. There are a number of good operating systems to use like UNRAID or TrueNAS/FreeNAS.
