NAS Buying Guide 2021

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Whether you already own a NAS device and want to upgrade it, or you're looking to buy one for the first time, this guide should make it easy.

We'll look at the most important variables and select component by component to find answers to the following questions.

  • Number of slots needed
  • Do I need support for expansion units?  
  • Do I want to use HDD, SSD, or a mix of both?  
  • Do I need a high-speed interface such as Thunderbolt3 or 10G networking?  
  • How much Processing power do I need ( CPU, RAM )
  • Do I need Plex Hardware transcoding? Do I need a GPU?
  • Do I need a specific feature that's only supported by one vendor OS?


These are the only questions you should worry about first. We won't worry about things like RAID, cloud access, add-on apps, mobile access, etc. as all of these features are standard on any reputable NAS.

1. number of bays: HDD/SSDs within a single NAS.

The number of bays is the maximum number of HDDs or SSDs your NAS can hold.

For example, the NAS on left has 4 bays, but you don't have to fill all the bays at once. You can mount 3 x 10TB hard drives in RAID5 today and add another drive to your RAID later as your data grows.

Most NAS have 3.5" bays (which can hold both 3.5" and 2.5" SSD/HDD), but there are also some slim NAS with only 2.5" drives. Then there are some Mixed Bay NAS that has both 2.5" and 3.5" bays. The NAS on the right is a mixed bay with 5+4 bays.

Number of Bays



There are 3 simple steps to calculating the number of bays. -

1. Take the total storage space you need and divide it by the size of the drive you want to use
2. Round the result up
3. Add 1 for RAID 5 or 2 for RAID 6

Let's take an example. You need 24 TB of storage and want to use 10 TB hard drives.

1. divide 24 by 10. that's 2.4
2. round it up. That's 3.
3. add 2 for RAID 6. that's 5.
 
So you can have a 5 Bay Machine with 5 x 10TB drives. The total RAW capacity would be 50TB and the usable capacity with RAID 6 would be 30TB (I know we calculated for 24TB, but we rounded up in step 2).
A little more about the last step. We added 2 for raid 6 in the last step because RAID 6 requires 2 additional drives. This spreads the data across all drives so that ANY 2 drives can fail without affecting your data. RAID 5 requires 1 additional drive, but can only handle the failure of ANY 1 drive. Don't settle for less than RAID 5.

Key Takeaway:  Find out the amount of storage you need, then determine the number of bays. Do the over-provisioning, you'll always need more storage than you think.

2. Choosing Storage Media for NAS: HDD/SSD Interface, Connectors and Form Factors

You know that HDDs have the lowest cost per TB and have a larger capacity compared to SSDs. But you don't have to choose just one. You can also use a mix of both.

There are 2 approaches to using SSD/HDD mix – Caching and Hot/Cold Volumes.

With Caching, you use large capacity HDDs for permanent storage and a fast M.2 NVMe SSD as a cache for temporary faster reads and writes of your frequently used data.

With Hot/Cold Volume, you use 2 volumes. One HDD volume for regular data and another SSD volume for data you need to access quickly.


If you know in advance the data you need to access faster, go with hot/cold volume. If you don’t know and would be willing to let the system decide based on your access pattern go with caching.  There is a third approach called auto-tiring too that keeps moving your data between media based on the access pattern but it's only used in enterprise environment.

Let's take a look at the Media Connectors and the interfaces. There are many but you would mostly end up using 3.5” SATA HDD, 2.5” SSD, or M.2 NVMe SSD ( marked with Common in the following image). Here is some major information about hard drives that you should know

Types of Hard drives and SSDs
  • The hard drive interface Disk Drives can be either SATA (single-path, 6GBPs) or SAS (dual-path, 12GBps). SATA is for home/SMB use and SAS is for enterprise use. Not all NAS support SAS media.
  • SSDs can have an NVMe interface in addition to SATA and SAS.
  • Standard SATA SSD and HDDs are most commonly used. Most NAS allow hot-swap.
  • SATA with M.2 connector ( M.2 SATA ) is a compact size factor available in SSDs. The compact size is the only advantage of this solution. Mostly M.2 SATA is used for intermediate storage as large capacities aren't available.
  • M.2 NVMe is a high-speed SSD and is very good for caching or high-speed volumes. If your NAS supports M.2 NVMe, you should make use of it.
  • U.2 is supported by very few NAS enclosures and is only used in an enterprise environment. It offers high capacity and is also hot-swappable.

Finally, there's the quality or purpose of the drive. Buy either a network drive ( Seagate Ironwolf, WD red, Toshiba N300) or an Enterprise Grade ( Seagate Exos, WD Ultrastar, Toshiba MG, Synology HAT5300). These drives are more reliable than desktop drives and are designed specifically for NAS.

Key Takeaway: A mix of SSD and HDD works best. Go for network or enterprise class media that gives you the lowest $ to TB ratio. For caching, use 2.5” SSD or if your NAS has it - M.2 NVMe


3. Network Speed and interface options for NAS


For the network interface, you have a choice between 1G, 2.5G, 5G, and 10G. However, you need a correspondingly fast network switch to achieve the speed.

Most entry-level NAS have a 1G network interface, although they are now moving to 2.5G.

If you still need faster access speed, you can opt for the 10G interface. The 40G interface is also supported by some NAS. SFP+ and 10GBaseT (RJ45) are popular interface options for 10G and 40G. For lower speeds, it is a simple RJ45 interface.

Finally, some NAS vendors like QNAP offer a Thunderbolt3 (40G) interface alongside the network so that a single device can be connected at the highest speed and others over the network.

Most NAS have multiple network ports that can be combined to increase throughput (called Team Up or Link Aggregation).

Key Takeaway: Try to buy a NAS with at least a 2.5G or 5G network, even if you have a 1G switch today. In the near future, all consumer-level switches will slowly move in this direction. If you need Thunderbolt3, there are few options, but choose according to your needs.

4. NAS Expansion: Scalable Storage for Future Data Growth

You may need to increase the storage space of your NAS as your data grows in the future. To increase the storage space, you can either replace the storage media with a higher capacity media (scale-up) or add another expansion unit that gives you more slots (scale-out).

With scale-out, your investment is protected because there are no drives to replace. But not all NAS support the expansion. For example, Synology DS -420+ is a 4-bay NAS, while DS -920+ is a 4-bay NAS that can be expanded to 9-bays with an expansion unit. If you anticipate you would have to expand in the future, go with DS-920+ so you can expand in the future when you need.

Key takeaway: plan according to the data expansion you expect in the future. It is always safer to buy a NAS that supports expansion.

5. NAS Computing Performance ( CPU + RAM)

Everything is tied to computing power so make sure it's not a bottleneck. Your network performance and your RAID reads-writes ( since most NAS have Software RAID) need processing power too, so it is important to have enough of it.

How much is enough depends on your actual usage. There is a NAS for almost every chipset - Annapurna Labs, Arm, Celeron, Ryzen, Core i3 i5 i7, Xeon, or Epyc - you name it. QNAP even has a model powered by the Chinese Zhaoxin.

If you are Run Virtual machines, multiple containers, Encrypt your disks or transcode videos, you should consider a powerful processor.

Manufacturers categorize their NAS by segments, and each segment is defined by what they do with their NAS. For example, an enterprise model has the highest specs (powerful processor, in some cases two controllers, two power supplies, ECC RAM, PCIe expansion....) because in an enterprise environment Inline Deduplication, compression, multiple VM storage, etc. are expected. So if you do not know, choose the best model in the segment you are in if you can afford it.

Key Take-Away : It is difficult to choose the processor. Look at the use case, if the vendor has it, and then decide. The more demanding your applications are, the better the processor should be. Start with little memory that you can upgrade later, but make a well-informed decision on the processor as it cannot be changed later.


6 . Plex : Hardare Transcode and resolution

If there's one application I am sure you'll use on your NAS, it's Plex, so plan for it. Fortunately, it's quite easy to do.

Plex's website has a list of all the recommended NAS models. It's clear from the list which models support hardware transcoding and up to what resolution. The higher the specification is, the better resolution is supported.
Be aware that hardware transcoding needs capable hardware and plex pass. In most of the cases you wouldn’t need hardware transcoding, go with a capable machine which plays full hd video with S/W transcoding.

7 . NAS Operating Systems

Each NAS vendor has its own operating system. Synology has DSM, Qnap has QTS, and Asustor has ADM, for example. It is the OS that you interact with, the interface that you see. All OS give you the basic features like user management, remote access, disk management, etc., but some vendors may have a few extra features that others do not.

For example, Synology has a backup suite integrated with OS called Active Backup for business. QNAP has wireguard VPN support out of the box and Asustor has a game streaming feature.

The good news is that most manufacturers use the same OS for all devices. So in theory you should be able to use all software features on all devices from a single manufacturer, hardware permitting. QNAP is an exception, having 3 different OS, each suitable for a different segment.
Once you know exactly what features you need, it's easy to research if the OS of the NAS you plan to buy has to those or not.

key takeaway - 90% of the features of all NAS operating systems are identical. It's the other 10% that can influence your buying decision. Although most NAS these days can run containerized applications, it's easy if the application/feature you are looking for is natively supported.

This guide is still a work in progress and we have tried to cover the topics we think are most important to a buying decision. If you have any questions, feel free to ask us. We promise to answer them for you.

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