NAS Buyers Guide

Network Attached Storage or NAS is a type of external storage device. The Network part refers to the fact that this type of storage sits on the network rather than being directly attached to the computer via, say, USB.

In this guide we’ll look at why you would want to use NAS, how to choose the right one for your purposes and the types of disk drives you can use in a NAS device. Let’s get started.

What is a NAS?

A NAS device is a storage device connected to a network that allows shared storage and retrieval of data from a central location for authorised network users. The NAS device is essentially a drive enclosure with space for multiple drives so are highly flexible and scaleable, meaning that as you need additional storage, you can add to what you already have. NAS is sometimes referred to private cloud, as it offers many of the features of shared cloud storage but it resides in your home or office.

NAS devices are usually suited to a home or small office environment as they are relatively simple to configure and operate so require no dedicated resource to support them - that said, as you’ll see later in this guide, they still have the capacity to scale to large capacities and have advanced feature sets for larger organisations too. They are low cost too, allowing the user to start small and add capacity as required whilst maintaining data integrity - the built-in data security feature called RAID that ensures data is protected in the event of a drive failure.

How to use this guide

There's a lot to consider when choosing a NAS so we've broken down this buyers guide into topics. If you don't want to read the whole buyers guide at once, or one topic is more important to you than the others, you can use the buttons in this index to skip to the relevant topic.

The Benefits of NAS NAS Enclosures NAS Software NAS Storage Drives NAS Optimised HDDs NAS Optimised SSDs NAS Drive Capacity NAS Accessories

The Benefits of NAS

Shared Data Storage

The most obvious feature of a NAS device is that it offers a shared storage platform. This means that multiple users can access the NAS to save and retrieve their files and data. Within the home this can be a useful feature to keep family media centralised, storing photos and videos in one place to keep the internal storage of phones and laptops uncluttered, but allowing access to all.

In an office environment, a NAS device is particularly useful when several people are working on the same files, so a single version can be maintained rather than multiple different versions scattered across devices. As the NAS device sits on the network it can be accessed externally via the router too, so workers from home have visibility of the centrally stored data too. We’ll come back to remote access later on in more detail.

Shared data storage also allows for shared back-up of devices - this can be set on each device to automatically schedule a back-up to the NAS, and furthermore the NAS itself can be backed-up to another device if required. This too can be set automatically to happen.


As we’ve mentioned a NAS device is essentially a drive enclosure, but with intelligence. Although they start from just two drive bays they scale much larger, and so it is common for users to grow into the space they have available. This can be done in two ways - firstly you can replace drives with larger capacity ones. For example a four bay NAS containing 2TB drives can be upgraded to 4TB drives thus doubling the capacity without replacing the enclosure.

Secondly, you can start with a larger enclosure, but leave some of the bays empty. There is no issue in doing this, as the enclosure will know they are empty and ignore them. You can then simply add drives as you go in order to increase the capacity.

It is worth mentioning that both these types of capacity scaling require the use of RAID settings, to ensure no data is lost when swapping out or adding drives, but we’ll come onto that shortly.

Data Protection

Perhaps the key feature of NAS when compared to the regular internal storage of a laptop or desktop PC is data security. A single internal drive in a computer may fail and all the data will be lost. Centrally saving data to a NAS device containing multiple drives allows for the CPU and memory in the enclosure to protect the data by way of employing RAID settings.

RAID or Redundant Array of Independent Disks is a technology that takes the separate storage drives within a system and splits data across these in various ways with the result of accelerating performance and in some instances protecting the data from single or in some cases multiple drive failure. So-called ‘parity’ blocks of data instructs the RAID controller where the data should be so if a drive fails, it knows what was on that drive and so can rebuild the array. It is essential to employ some level of RAID where the OS should be protected and / or data is mission critical, such as a server. Let’s look at the options available.

RAID 0 - This method of RAID stripes the data across a minimum of two disks. Generally speaking, RAID 0 increases the read and write speeds proportionally to the number of disks you use, however although no capacity is lost with the array, there is also no fault tolerance, so RAID 0 may not be ideal for critical data storage.

RAID 1 - This method of RAID mirrors the data across a minimum of two disks. Although half the total capacity of the RAID is lost, for example two 1TB disks will result in 1TB of useable capacity, in the event of one drive failing, the system can be turned off, the failed drive replaced and then the mirror rebuilt. This is a popular data security solution but can be costly on drives bearing in mind half the capacity is lost.

RAID 5 - Here, data is striped across a minimum of three disks with a single parity block. Only a quarter of the total capacity is lost, for example three 1TB disks will result in 2TB of useable capacity. Should a drive fail the distributed parity block allows a drive to be replaced and the array rebuilt.

RAID 6 - This is an enhancement to the technology used in RAID 5 – with this method data is striped across a minimum of four disks, but with two distributed parity blocks – although a greater degree of useable capacity is lost, for example four 1TB disks will result in 2TB of useable capacity, it has the benefit that two drives can fail before you lose any data. This can be a key factor if employing large drive sizes (4TB and above), as rebuild times can be significantly lengthened.

RAID 10 - This method of RAID employs a minimum of four drives, and features two striped RAID 0 arrays mirrored in RAID 1, giving the best possible performance while providing some redundancy against drive failure. For example four 1TB disks will result in 2TB of useable capacity. Data integrity is very high, as the array will tolerate a drive failure in each of the mirrored blocks, but again it should be noted that as larger capacity drives are used, the rebuild times in the event of a failure are significantly lengthened.

Depending on how the RAID setup is controlled it is possible to have multiple arrays working independently. For example two OS drives can be mirrored in RAID 1, whilst four storage drives could be configured in RAID 5. Alternatively two RAID 6 arrays of 5 drives could be created in a 10 drive storage device. Let’s look at the ways RAID can be controlled.

NAS Enclosures

Form Factors

There are two common types of NAS enclosures - desktop and rackmount. As the first suggests this simply sits on a desk or table top and has a cable connecting it to the network. The rackmount type is designed to fit a standard 19” wide computer rack cabinet in a server or coms room. As you may expect the rackmount type are usually higher specification devices as they are intended for much larger organisations. They will typically scale to larger capacities and have greater software feature sets. Desktop devices usually top out at 12 drives bays whilst rackmount models offer up to 24 bays.

It is worth mentioning here that both types can be expanded beyond the physical limits of the single chassis by adding an expansion chassis to the desktop NAS or an extra disk shelf to the rackmount NAS. We’ll cover this more later but clearly if larger expansion is likely in your scenario even a small rack cabinet setup may be advisable.

NAS Processors

The processor (or CPU) in a NAS is essentially the brain, controlling how data is written to the drives and the speed at which it can be retrieved. Normally if you are buying a PC for home or work, you are buying it based on its ability to do tasks as quickly as possible. However, a NAS will often be on for days, weeks or months at a time, unlike your desktop PC. Plus most of the tasks it performs are passive or require much less CPU power. The result is that the CPU found in most NAS appears to be rather modest when compared to the desktop computer alternatives, as the CPU needs to be more efficient about power consumption and heat.

Because of these differences from PCs the processors seen in entry-level and mid-range NAS devices are often ARM based such as Marvell, Annapurna or Realtek - alternatively they may be the less powerful Intel x86 models such as Intel Atom or Celeron. These are all perfectly adequate to perform basic NAS features, although if you intend heavier usage of applications then consider quad-core processors rather than dual-core.

Although it is difficult to guarantee a performance level due to factors like number of users and speed of network connection, these following pointers offer some insight as to how to best choose a NAS depending on it’s CPU:

Advantages of low-cost CPUs:

• Lower cost of CPU hardware means that the overall cost of NAS is lower
• Lower spec CPUs consume less power helping to reduce running cost
• Lower cost CPUs are still powerful enough to handle DLNA Media streaming, typical file level exchanges and backups
• Can support surveillance based NAS use and multiple IP cameras but will see limitations as numbers increase

Disadvantages of low-cost CPUs:

• Will struggle if many users are connecting concurrently
• The majority cannot handle transcoding, large-scale rendering or 4K media
• Higher-end software features sets will not be able to run on low-cost CPUs

It is worth mentioning that there are NAS devices at the mid to higher end using Intel Core i7, AMD Ryzen or even Intel Xeon processors but these are squarely aimed at the business and enterprise markets where large data sizes are the norm and fast Internet connectivity are required.


The amount of memory (or RAM) required in a NAS will largely depend on the applications and number of users using the NAS at any given time. It is generally a rule of thumb that if your NAS is going to be used by more than 5 people and for backups and multimedia, then you should have at least 2GB of memory to ensure completely fluid activity. It is recommended to go for at least 4GB if you are using RAID settings in this same scenario. If, however, you are going to use a NAS for business, large-scale surveillance with multiple IP cameras for CCTV, or to run multiple virtual machines (VMs) for users to have their own bespoke virtual desktop, then you will need to start with at least 8GB of memory. It is worth bearing in mind that large rackmount NAS devices are essentially storage servers so they scale in RAM as a server - up to 512GB.

In many cases, it is possible to expand the memory in NAS device, just like a PC or workstation, so you should look out for this ability if you intend for your NAS use to scale. All NAS manufacturers will provide a compatibility matrix to ensure you choose the correct RAM if deciding to upgrade - either by purchasing the branded memory or a compatible alternative.

NAS Drive Bays

Although we’ve addressed CPU and RAM first, it is fair to say that as a NAS enclosure increases in drive capacity space, then the specifications of the system will also increase in anticipation of heavier workloads, more users and more intensive applications. As we’ve mentioned NAS devices start at two bays the smallest NAS designed mostly for home use but still offering basic RAID options to afford some data protection, and scale to 24 bays in a single rackmount chassis offering much greater RAID flexibility.

The drive bays themselves are not that different regardless of which model you choose. Most will be covered with a banking plate when no drive is present, and when drives are in place they can be removed by flipping a small lever or clip at the front.

The vast majority of NAS drive bays are hot-swappable - a feature that allows you to take out the drive and replace with a new one (either after failure or for upgrade), without the need to power down the system. Although RAID settings are required to effectively use this feature, it does make maintaining your data very simple. If you want this feature then avoid the very lowest models of NAS, as they tend to be fixed drives that you cannot access from the front of the enclosure.

The majority of drive bays are 3.5in slots featuring SATA III connectors that will take either 3.5in or 2.5in hard disk drives (HDDs) or solid state drives (SSDs). Some NAS chassis also feature dedicated 2.5in drive bays aimed specifically at SSDs for advanced high speed caching. A more recent development is the inclusion of multiple M.2 slots internally to enable tiered storage support in a single device being used for fast access and archive purposes.


NAS devices come with a variety of connections as standard, although the number and type will vary on whether it is an entry-level unit or a higher-end appliance. Let’s take a look at what you might see.

Network - As this guide is dealing with NAS - network attached storage - the very minimum every NAS device will have is an RJ45 Ethernet network connection. This will usually be 1GbE. Ethernet is by far the most common network connectivity standard around and Gigabit speed connections are common on most desktop PC or workstations today. Some mid-to-higher end NAS devices will feature 10GbE offering 10x the performance when used with a 10GbE network throughout - this will be primarily restricted to business use.

It is also common as units increase in price and performance that multiple (two or four) Ethernet ports will be featured, sometimes in combination - 2x 1GbE and 2x 10GbE. This is designed to give options for connectivity and to provide link aggregations features, where two or more ports can be combined to give a greater throughput speed - 2x 10GbE = 20GbE. Alternatively the different ports can be used for failover - redundancy in case one connection should daces working.

USB - a single or several USB ports may be provided. Any front mounted USB ports are usually for the direct upload of data from an external drive onto the NAS device, whereas any rear mounted ports are intended for connection to an external storage drive to back up the NAS to.

eSATA - some NAS devices come with an eSATA port. Usually this interface allows the connection of external drives that have the eSATA interface, with the intention of expanding the capacity of the NAS device.

Expansion ports - we mentioned earlier that some NAS devices can be expanded, but rather than using a third-party connection such as USB or eSATA, they come ready with one or more expansion ports in order to connect a second expansion chassis - usually almost identical to the original NAS unit but with no inbuilt intelligence. We’ll come back to these later.

NAS Software

Operating Systems

As we’ve touched on previously the basic functions of the NAS device are to store and share data, acts as a back-up and protect data via RAID technology. However, leading NAS brands such as Synology and QNAP have taken the feature set several steps further and enabled a whole host of additional functions. We’ll take a look at some of these but it’s always worth remembering the OS on most NAS devices will be the same, but some functions may be limited by the CPU power and RAM available. If you know you want advanced functionality then purchasing a higher-end machine is the way to go.

It is also worth mentioning that the installed operating systems are regularly being upgraded so you’re always able to take advantage of new NAS features without the need to change your hardware.


Configure, maintain, and monitor every facet of your NAS - no IT professional required.

File Syncing

Sync your files securely between multiple computers, servers, and public clouds.

Data Backup

Protect personal data on VMware, Windows endpoints, and SaaS applications.

NAS Protection

Protect data on NAS against unexpected hardware failure, natural disasters, and accidental deletion.


Provide a complete vitualization solution with Virtual Machine Manager.


Boost productivity with Office and Drive, streamline projects with Chat, set up a private mail solution, and so much more.


Enjoy photos, videos, and music through an intuative web and mobile interface.

Data Security

Industry-leading security solutions defend your NAS from sophisticated threats.

Additional Software

As the points touch on above mid to high-end NAS devices are essentially small office servers and they can be used in this way providing email and productivity applications. To this end some NAS models are equipped with the ability to support most virtualisation solutions to enhance work efficiency whilst keeping an easy management interface.

Check for compatibility if you're looking to use your NAS in this way.

NAS Storage Drives

We’ve mentioned that the 2.5in and 3.5in drive bays in a NAS device will support both hard disk drives (HDDs) and solid state drives (SSDs). Whilst it is true that you can install any compatible HDD in a NAS, it isn’t recommended as most regular drives are designed for occasional use rather than 24/7 use that is more often seen when running a NAS. Performance will suffer and the life span of the drives will shorten - you may save money but will spend more time rebuilding the drive array as failure rate will be high. It is worth mentioning here that you can purchase NAS systems with drives already pre-populated inside and these can often be more cost effective.

As alluded to, the main drive manufacturers, like WD and Seagate have developed NAS hard drives - specifically designed and tested to be operated for longer times or continuously - a longer warranty period is standard on these drives too in line with these features.

NAS Optimised HDDs

Seagate IronWolf Family

These Seagate NAS specific drive ranges come in two versions - IronWolf is aimed at Home, SOHO and small business NAS drives with up to 8 drive bays. IronWolf Pro, on the other hand is for businesses and digital artists who need extremely high performance from their NAS servers.

Ironwolf Ironwolf Pro
Capacity 1TB - 12TB 4TB - 18TB
Form Factor 3.5in 3.5in
Interface SATA 6Gb/s SATA 6Gb/s
Recommended Drive Bays 2-8 8-24
Spindle Speed 5900rpm 7200rpm
Cache 64MB 128MB
Warranty 3yrs 3yrs

Seagate SkyHawk

The Seagate SkyHawk range is aimed at surveillance-specialised storage. SkyHawk is designed and purpose-built for surveillance applications featuring ImagePerfect firmware that is designed to ensure seamless video footage capture in 24/7 surveillance workloads scaling to concurrent video capture from up to 64 HD cameras. The AI version feature ImagePerfect AI technology that enables an additional 32 streams for deep learning analytics within the system.

SkyHawk SkyHawk AI
Capacity 1TB - 8TB 8TB - 16TB
Form Factor 3.5in 3.5in
Interface SATA 6Gb/s SATA 6Gb/s
Recommended Drive Bays 2-8 8-24
Spindle Speed 7200rpm 7200rpm
Cache 64MB 256MB
Warranty 3yrs 3yrs

Seagate Exos

Designed to handle the most rigorous workloads with capacities up to 16TB, the Seagate Exos enterprise class drives are perfect high-reliability solutions for servers, storage systems, and business-centric NAS systems.

Exos X Exos E
Capacity 10TB - 16TB 300GB - 8TB
Form Factor 3.5in 3.5in
Interface SATA 6Gb/s SATA 6Gb/s / SAS 12Gb/s
Recommended Drive Bays 8-24 8-24
Spindle Speed 7200rpm 7200 / 10000 / 15000rpm
Cache 256MB 256MB
Warranty 5yrs 5yrs

WD Red Family

With drives up to 14TB, the WD Red series offers a wide array of solutions for customers looking to build a high performing NAS storage solution. WD Red and Red Plus drives are built for up to 8-bay NAS systems, and pack the power to store your precious data in one powerhouse unit. Increase the efficiency and productivity of your business with WD Red Pro drives, available for up to 24-bay NAS systems. Engineered to run cool and quiet and specifically designed for RAID environments, they feature noise and vibration protection to prevent excessive wear and tear from spinning constantly within a NAS array.

WD Red WD Red Plus WD Red Pro
Capacity 2TB - 6TB 1TB - 14TB 2TB - 14TB
Form Factor 3.5in 2.5in & 3.5in 3.5in
Interface SATA 6Gb/s SATA 6Gb/s SATA 6Gb/s
Recommended Drive Bays 2-8 2-8 8-24
Spindle Speed 5400rpm 5400rpm 7200rpm
Cache 256MB 256 - 512MB 256 - 512MB
Warranty 3yrs 3yrs 5yrs

WD Purple

WD Purple surveillance HDDs are engineered specifically for surveillance security systems and tuned for write-intensive, low bit-rate, high stream-count applications typical to most surveillance applications. They include AllFrame technology, which improves video streaming, helping to reduce errors, pixelation, and other video interruptions that could happen in a video recording system. WD Purple drives have an enhanced workload rating that supports systems designed for 24x7 video recording with up to 64 cameras. The 8TB, 10TB, 12TB, and 14TB capacities feature AllFrame AI technology that enables an additional 32 streams for deep learning analytics within the system.

WD Purple WD Purple AI
Capacity 1TB - 6TB 8TB - 14TB
Form Factor 3.5in 3.5in
Interface SATA 6Gb/s SATA 6Gb/s
Recommended Drive Bays 2-8 8-24
Spindle Speed 5400rpm 7200rpm
Cache 64MB 256 - 512MB
Warranty 3yrs 3yrs

NAS Optimised SSDs

Installing SSDs in your NAS can mean better performance when it come to demanding applications such as 4K video or editing large file sizes where fast caching will be beneficial. They are also very much suited to the units we’ve mentioned where dedicated 2.5 inor M.2 slots are provided to deliver enhanced caching. It is worth pointing out though, that although SSDs may provide benefits for local users (those within the same network as the NAS device), external users’ experience will more likely be governed by their network access speed rather than the internal drive capabilities.

SSDs may also be preferable in an environment where noise and/or heat could cause an issue, as they operate much quieter with minimal heat due to no moving parts.

Seagate IronWolf SSDs

Seagate IronWolf SSDs are built specifically for NAS use and offer capacities ranging from 240GB to 4TB. Each drive includes AgileArray firmware to keep your NAS enclosure maximised for demanding 24/7 and multi-user environments, and can be used in an all-flash array or in a NAS capable of tiered caching.

Ironwolf SSD Ironwolf M.2
Capacity 240GB - 4TB 240GB - 2TB
Form Factor 2.5in M.2 2280
Interface SATA 6Gb/s NVMe
Recommended Drive Bays 2-24 N/A
Warranty 5yrs 5yrs


Unlike standard SSDs, WD Red NAS SATA SSDs are specifically designed and tested for 24/7 usage. This durability together with efficient caching of big files make these drives ideal for databases, multi-user environments, photo rendering, 4K and 8K video editing and other demanding applications. With 2.5in and M.2 form factors and capacities from 500GB up to 4TB the WD Red SSD range lets you optimise your existing or next NAS system for superior performance and endurance.

Capacity 500GB - 4TB 500GB - 2TB
Form Factor 2.5in M.2 2280
Interface SATA 6Gb/s NVMe
Recommended Drive Bays 2-24 N/A
Warranty 5yrs 5yrs

We’ve covered the drive families specific to NAS use in this guide, but to understand more about whether HDDs or SSDs are the right choice for your NAS, please read our Internal Storage Buyers Guide.

NAS Drive Capacity

Whilst drive capacity and overall capacity will be down to your individual scenario, and be dependent on your need for storage now plus future expansion requirements, it is worth remembering that as drive capacities increase, so does rebuild time for an array should one (or more) fail. I you need access to mission critical data then a larger NAS array with smaller individual capacities may be the better option.

4x 8TB = 32TB
Less RAID flexibility with 4 drives
Long rebuild times

8x 4TB = 32GB
More RAID flexibility with 8 drives
Shorter rebuild times

NAS Accessories

Expansion Chassis

As we touched upon in the connectivity section, both desktop and rackmount NAS can be directly expanded using additional chassis if eSATA or expansion ports are featured on the back of the unit. Essentially the expansion unit is a second chassis or additional rack shelf full of drives connected to and controlled by the original NAS device so the whole drive pool capacity is seen as a single entity.

Add-in Cards

Add-in cards for a NAS are just like those for a PC or server, in that the use a PCIe slot on the NAS motherboard to provide additional functionality, capacity or connectivity. Once again it is usually the mid-range to high-end range of NAS devices that will support slots for add-in cards. Some of the options available include:

M.2 SSD / 10GbE Combo Card

M.2 NVMe SSD Card


2x 10GbE Card

2x SFP+ 10GbE Card

SAS Expansion Card

The Best NAS

We hope you’re found this guide to NAS systems useful helping you choose your base system and storage drives. Click below to see our range of products.


Remember we’re here to help you select the internal storage drives best suited for your purposes, so don’t hesitate to contact our friendly advisors on 01204 474747, if you’d like further advice.