Should You Buy a 2-Bay or 4-Bay NAS Drive in 2021?

Choosing Between Buying a 2-Bay or 4 Bay NAS

For many users who decided to make the switch from subscription-based Cloud services and to their own private NAS server, it can be tricky to understand exactly what they need in terms of storage and power. Network-attached storage NAS has evolved rapidly over the years and now there is a tremendous range of solutions that vary in size and ability to choose from, often resulting in the most expensive servers not always being the most capable. One of the first hurdles that many users encounter when choosing their first NAS drive is choosing between a 2-bay NAS and 4-Bay. With the majority of NAS brands out there offering most standard solutions and across different hard drive scales, choosing between these different sized NAS is not as straightforward as one might think. So today I’m going to talk to you about the differences between each, which one is the best value, their advantages and hopefully help you decide which one best suits your storage needs. Let’s start.

2-Bay vs 4-Bay NAS – Storage, Expandability and Capacity

On the face of it, it seems pretty obvious that a 4-Bay NAS model with its increased storage bays will be the better storage option overall. How on earth can a NAS device that is 50% less in media bays possibly compete?!? Well, in recent years the largest available capacity in hard drives has massively increased and therefore the total potential terabytes available for each media bay has grown drastically. Yes, you could fully populate a four-Bay NAS with 4TB hard drives, but you could always just use a single 12TB hard drive at a lower price per TB in 2021 and regardless of whether you use RAID 0 or RAID1 with two disks, still have a huge capacity in a 2 Bay NAS. Additionally, these days a number of brands provide the same level of external enclosure expandability on both the 2-Bay and 4 Bay NAS systems (eg DS920+ / DS720+ and TS-253D / TS-453D), therefore 2-Bay NAS does not have the lower metaphorical glass ceiling that it once had in terms of additional storage down the line. Indeed, you can even expand a RAID 1 to a RAID 5 on a 2-bay but spreading it over both the NAS and expansion enclosure at once, to provide an excellent way to still increase the storage on your 2-Bay later on and not feel trapped within its dual media design architecture.

However, this is not quite as cut and dry as it appears. Despite the improvements in 2-Bay NAS architecture in recent years, there is always going to be one big day 1 advantage in the flexibility of 4 Bay NAS that 2-Bays cannot really match. That is that you do not necessarily need to fully populate a 4-bay on day one and many users go ahead with just putting two hard drives inside a 4-Bay NAS in a RAID 1 at the start. Not only does this give you exactly the same level of storage and performance that you would find in 2 Bay NAS, but it also allows you to add drives to this partially populated NAS and expand its storage pool from a RAID 1 to a RAID 5, increasing the total storage gradually throughout the lifespan of the system, WITHOUT buying a whole expansion chassis. This allows flexibility in how much storage you use now and how much you need to graduate to later at a minimal cost at the start. In summary, although 4 Bay NAS is still technically the better storage, flexibility and capacity option, a 2-Bay is not necessarily as inferior as it once was.

2-Bay vs 4-Bay NAS – Price and Value

This is an often underestimated factor in choosing between a 2-bay or 4-bay NAS system. Many people assume that a 4-Bay NAS costs more money to buy and even more money to populate. Although this is still technically true, it is hardly any more expensive to operate a 4-bay NAS 24×7 than a 2-bay. As far as actual day 1 costs go, notwithstanding the flexible storage installation mentioned in the previous subject, 4-Bay NAS systems allow you to use smaller capacity hard drives in order to match the same storage on larger hard drives. What this means is that a 4-ay NAS allows you to install four 4TB drives inside in a RAID5 and arrived at a lower price per terabyte than 2x 12TB drives. Depending on how you scale your storage and the number of drives you use, 2-Bay shares and 4-Bay NAS can retail at a similar price point and will differ only depending on the drive you choose and the RAID configuration you opt for.

Likewise, returning to the point of the cost of 4-bays as being more expensive than 2-bays, the newest generation NAS drives will often barely be more than $100-150 difference in their prices between 2 and 4 bays and are largely identical in CPU, Memory and ports in every other way. 4-Bays may seem like a bigger chunk of money (especially for those already feeling stretched on a prosumer 2-Bay) but if you are prepared to perhaps drop the capacity you have in mind 1-2TB  (i.e purchase 4TBs, not 6TBs)  to compensate this price difference, the result will be that your 4 Bay NAS can achieve much higher read and write speeds with more drives being accessed simultaneously, whilst also opening the door to dual-drive redundancy configurations (i.e RAID 6) and will ultimately provide a more responsive, higher performing and data safe NAS for all of your needs.

In summary, the savings available in choosing a two-bay over a four-bay can easily be countered in the grand scheme of things by scaling the capacity or architecture of the HDD you choose to put inside. The money saved in a 2 bay might well be money you need to spend a year or two down the line.

2-Bay vs 4-Bay NAS – Power, Performance and Speed

As mentioned, using 4 hard drives in a RAID 5 will likely provide better performance than two drives in a RAID 1 environment. This performance can be measured by traditional direct read and write activity between your client hardware and your NAS, or it can be measured by the performance of individual applications and services from within the network-attached storage drive itself (i.e the NAS software and services). When looking at buying your first NAS, many will overlook 2-Bay’s simply because of this performance boost available in the 4-Bay alternative models. However, enterprise-grade/Pro hard drives Seagate ironwolf Pro or EXOs) will often provide performance benefits in a RAID 1 environment that can surpass the use of standard hard drives in a RAID 5. Of course, Pro series drives cost $40-50 more per drive, but also have longer warranties, data recovery services, more onboard cache and faster rpm to increase that read and write speed, so you get more for your money ultimately. Additionally, if you plan on taking advantage of 10Gbe, either with a port already on your NAS or as an upgrade down the line via PCIe, then you are much, MUCH better off with a 4-Bay NAS, as a 2-Bay (even if populated with the latest generation SATA SSDs) cannot fully saturate 1,000MB/s.

Finally, it is worth discussing that a large number of modern 4-Bay NAS systems in 2021/2022 arrived with dedicated SSD caching bays. These bays do not replace the existing SATA hard drives and are parallel media bays that allow you to install M2 NVMe SSD to improve the internal performance of your NAS by copying more frequently accessed files partially or fully onto the SSD to reduced access time to these more popular pieces of data. Although a handful of 2 Bay NAS systems have arrived on the market with support of dedicated SSD caching bays (Lockerstor 2 and DS720+), the feature is still more available on foUr Bay solutions and for many users that want to graduate the utility of their NAS from home to prosumer and inevitably into business use, the ability to upgrade internal performance in this way can often sway buyers to opt for a 4-bay NAS.

2-Bay vs 4-Bay NAS – Power Use, Noise and Deployment

Unsurprisingly, the bigger the NAS drive, the more power it will consume. When comparing like-for-like deployments in similar architecture on 2-Bay and 4-Bay NAS, the latter will always use a little bit more. This is the reason that you will generally find that the PSU on a 4-Bay NAS is always of a higher what rating. However overall, unless you are pushing the system particularly hard, the simple act of adding two more SATA hard drives will generally make a minuscule difference and is hardly a reason to compare these two overall – A PSU power rating is the MAXIMUM draw it can make, not the amount it will be using constantly! However, in terms of vibration generated when the system is in operation and the rise in assisted fan operation as usage increases, generates more heat which makes a noticeable impact on the ambient noise generated when you are running a 2-Bay vs a 4-Bay.

The power difference will still remain rather small as these are still quite small components but if you are especially sensitive to noise then the increased drive and fan-based sound will annoy you. Additionally, this increase in ambient noise generation scales accordingly if you use larger capacity drives or more enterprise-level hard drive builds. So therefore if you are looking at a 2-Bay NAS with bigger capacity hard drives, it will still generate a comparable level of ambient noise that a 4-Bay would when populated with standard class NAS media or smaller capacities. Now that brands like Seagate and WD have reshaped their respective portfolios for NAS hard drive media in a way that ALL large capacity hard drive (eg 10TB and above) are Pro class (i.e noisier), it makes the lines increasingly blurry between 2-Bay and 4-Bay NAS noise levels. Below is an example of the noise difference between a standard class and pro class drive noise generation in just a single drive. It may seem a tad irrelevant, but it’s important if you are a user looking to go for a smaller NAS with BIGGER drives:

WD Red NAS Hard Drive Noise Test WD Red PRO NAS Hard Drive Noise Test

2-Bay vs 4-Bay NAS – Conclusion

So as you can see, the difference between a 2-Bay and a 4-Bay NAS is a great deal more than the number of available hard drives you can use. Each kind of NAS system can have its performance, capacity, ambient noise and power consumption scaled in a multitude of ways in order to facilitate the best possible network attached storage solution for you. Users on a tight budget might all too soon end up purchasing a 2 Bay NAS without realising that a 4-Bay has scalability that can save you money down the line. Likewise, users who like to invest a little bit more long term or prefer their NAS investment to be a little bit more spread over the lifespan of their product will tend to err towards a 4-Bay solution, without realising that a 2-Bay is still quite viable in the short term and modern scalability of NAS means taht a 2-Bay NAS is not quite the dead-end it once was! Below I have detailed some of the BEST examples of 2-Bay and 4-Bay NAS Synology, QNAP and Asustor that are great examples of margins between each tier has become spectacularly narrow.  If you are still unsure on how to proceed, be sure to take advantage of the free advice service here on NASComapres using the boxes at the bottom. We (me and Eddie the web guy!) answer every email and do it without profit in mind (i.e it’s absolutely free), so though it might take an extra day for us to reply, we will get back to you with recommendations on the best solution for you.

Synology DS720+ 2-Bay – $399+

Synology DS920+ 4-Bay – $559+

J4125 4-Core CPU – 2/6GB DDR4 – NVMe SSD – 2x1Gbe


J4125 4-Core CPU – 4/8GB DDR4 – NVMe SSD – 2x1Gbe


QNAP TS-253D 2-Bay – $389+

QNAP TS-453D 4-Bay – $549+

J4125 4-Core CPU – 4/8GB DDR4 – PCIe Slot – HDMI – 2×2.5Gbe


J4125 4-Core CPU – 4/8GB DDR4 – PCIe Slot – HDMI – 2×2.5Gbe


Asustor Lockerstor 2 2-Bay – $379+

Asustor Lockerstor 4 4-Bay – $499+

J4125 4-Core CPU – 4/8GB DDR4 – NVMe SSD – 2×2.5Gbe J4125 4-Core CPU – 4/8GB DDR4 – NVMe SSD – 2×2.5Gbe




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    37 thoughts on “Should You Buy a 2-Bay or 4-Bay NAS Drive in 2021?

    1. Great explanation, been looking into these things ever since having… Issues with my laptop. For my own uses, I’m going to start with the two bay for now personal use. If my future plans turn out I’ll definitely have to do a 4 bay, but at that point it’s not a total loss – I can still user the 2 bay as a personal backup, use the 4 bay as a business write off, and there would still need the option to expand using both. For me either of pretty much solely going to see use as data backup.

    2. Thanks for this video, i was worried about my 16tb wd red, it’s in a fractal brand computer case and the drive ebay is a bit loose so it makes a lot of rattling noise each time it wakes up from sleep mode, the drive is steady secure screwed in the sliding tray but the tray vibrates in the drive bay slot and makes a lot of metal noise.

    3. After years and years, I’d suggest going with as large as you can go for the number of drive bays. If you were considering a 2 bay, go for the 4 bay.. If you were considering the 4 bay- consider heavily going to a 6 or 8 bay – if you can afford it and if the system is upgradable in a manner that makes sense to you.

    4. This is an awesome video, lots of details in it like, how many watts they may consume in comparison between each other.
      According to all you’ve explained in this video, you really kinda convinced me to buy 4 Bay NAS. However, I’m still thinking about it, about, how am I going to use it.
      I’m a newbie software developer and, I kinda think that the this will be very useful especially when I need to reach my data outside of my flat. But, will I be still needing 4 Bay?
      Also another question I have, QNAPs have HDMI input, but I’ve heard that Synology has a lot better software support. Is there a super duper reason which may make me prioritize NAS with HDMI input?
      My budget is anyway limited. But hey, I’m thinking about either buying 4 Bay Synology (currently 570 € in Germany), or, 2 Bay QNAP (currently 280 € in Germany), or, Canon G6050 printer (currently 300 € in Germany). Very difficult to decide. I may buy a printer and a 2 Bay NAS instead of 4 Bay… Any ideas? 🙂 Thanks in advance.

    5. The data itself is on an HDD from the beginning. Seems you are testing the read limits of your HDD, thats all. I’m copying 12GB of data to an NVMe storage in less than 1 minute, and thats with USB3.0. With thunderbolt it’s only a few seconds. The limiting factor is then your connection speed like 1GBE or 10GBE. Copying internally without any connection should do the best out of it, but your limit is the reading speed of your HDD, where the data is stored.

    6. I use my 2 bay Synology DS720 for Plex. I store my photos on it and that’s about it. So a two bay with two 4tb drives in is fine. Had it a year and I am up to 1 tb used so plenty to go. Upgrade when the time comes will be in drive size not extra bays
      I back up to external drives with them being directly attached to the NAS. I back up Apples Time Machine to a size restricted volume in the pool. That’s because Time Machine will fill up all available space if given free reign.
      So I’m happy with my Raid 1 2 bay. It does the job for me

    7. bought a WD Red pro 16tb for my Zapitti…..not too bad when i play my SD tv shows….. prob is when i play my larger 4k movie files….. knocking noise can be heard across the room>>.,,,, getting most annoying???….

    8. ….Should i buy 2x Samsung SSD 970 EVO Plus 250GB, M.2 (MZ-V7S250BW) …for a DS920+ ??? …many people say if the „Wear_Levelling_Count“ (Samsung Life Span Figure) is reached they (Synology) shut it off. And many people say it only last about 2 years!

    9. I beleiev that cache is more important in applications such as VM’s or docker .. mainly applications which repeat a lot like running mqtt for a vast automation … where the same data will go back and forth on a daily basis .. that’s where the cache would excel ..

      I also believe that you don’t need the nvme for cache as SATA/sata nand will suffice … Unless you have 10gbit network which requires 1gb to be transfered in ms which is not for home applications anyhow ..

    10. I bought a cheap $100 ZyXEL NAS326 and threw in a moderately silent 8TB WD drive. Somehow, it amplified the sounds made by the drive 25x. I can literally hear the damn thing through the wall which is completely unacceptable given that I couldn’t hear it when the drive was in my PC.

    11. Can you change your raid config from say a 5 to a 6 without loosing all your data? What if I have a raid 5 now but I am upgrading how many bays I have and would like to have raid 6. Is this possible? What if I have the whole drive backed up and can fully restore all my drives. Can I start over with a raid 6 then restore from my back up?

    12. As someone who uses a 4TB drive in his PC for media storage over the last year and have used approximately 2/3 of it, I’d probably go for the 4-bay option and start with a pair of 4TB drives and then add more drives with more capacity as needed over time. As drives fail I can replace them with bigger drives over time.

    13. The lower cost of smaller drives could also be due to SMR (Shingle Magnetic Recording) on the non “pro” drives this shouldn’t really be an issue for most consumer users but for high usage users this is where the pain comes in.