NAS (Network Attached Storage) refers to a type of standalone external storage. It references the way that this type of storage sits on a network, rather than being directly attached to the computer via, say, USB. In this guide we’ll look at how NAS differs from storage in PCs or workstations and why you would want to use it, how to choose the right one for your purposes and the types of HDD and SSD you should use in a NAS box.

NAS boxes are ideally suited to a home or small office environment as they are simple to configure and operate. That said, as you’ll see later in this guide, they still have the capability to scale to large capacities and have advanced features for larger organisations too. NAS boxes are relatively low cost too, allowing you to start small and add capacity as required while maintaining data integrity using the built-in data security feature called RAID that ensures data is protected in the event of drive failure.

NAS device introduction image representing a home or office network storage setup

The Benefits of NAS

Shared Data Storage

The most obvious benefit of a NAS box is that it offers a shared storage platform. This means that multiple devices and users can access the NAS over a network 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.

Illustration showing multiple users accessing shared data on a NAS system

Scalability

As we’ve mentioned a NAS box 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.

NAS enclosure with multiple drive bays demonstrating upgrade potential

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 - this is covered on the next tab.

User installing additional drives into a NAS to expand storage capacity

Data Security

When considering HDD or SSD purchases for a NAS, it is vital to understand about how best to protect the data on your drives. This can be achieved in a number of ways using RAID technology. RAID stands for redundant array of independent disks and it is essentially spreading the data over multiple drives to remove the chance of a single point of failure.

It works by blocks of data, referred to as 'parity' blocks, being distributed across the multiple drives so that in the event of failure of any one drive the parity blocks can be used to retrieve the lost data and rebuild the array. RAID levels are categorised by number and their attributes vary with each type.

RAID 0

RAID 0 is the fastest RAID mode since it stripes data across all of the array's drives and as the capacities of each drive are added together it results in the highest capacity of any RAID type. However, RAID 0 lacks a very important feature - data protection. If one drive fails, all data becomes inaccessible, so while RAID 0 configuration may be ideal for gaming where performance matters but data is not critical, it is not recommended for storing critical data.

Diagram showing RAID 0 striping across multiple drives with no redundancy

RAID 1

RAID 1 works across a maximum of two drives and provides data security since all data is written to both drives in the array. If a single drive fails, data remains available on the other drive, however, due to the time it takes to write data multiple times, performance is reduced. Additionally, RAID 1 reduces disk capacity by 50% since each bit of data is stored on both disks in the array. RAID 1 configurations are most commonly seen when mirroring drives that contain the operating system (OS) in enterprise servers, providing a back-up copy.

Diagram showing RAID 1 mirroring between two drives for redundancy

RAID 5

RAID 5 writes data across all drives in the array and to a parity block for each data block. If one drive fails, the data from the failed drive can be rebuilt onto a replacement drive. A minimum of three drives is required to create a RAID 5 array, and the capacity of a single drive is lost from useable storage due to the parity blocks. For example, if four 2TB drives were employed in a RAID 5 array, the useable capacity would be 3x 2TB = 6TB. Although some capacity is lost, the performance is almost as good as RAID 0, so RAID 5 is often seen as the sweet spot for many workstation and NAS uses.

Diagram showing RAID 5 setup with distributed parity across multiple drives

RAID 6

RAID 6 writes data across all drives in the array, like RAID 5, but two parity blocks are used for each data block. This means that two drives can fail in the array without loss of data, as it can be rebuilt onto replacement drives. A minimum of four drives is required to create a RAID 6 array, although due to the dual parity block, two drives capacities are lost - for example if you had five 2TB drives in an array, the usable capacity would be 3x 2TB = 6TB. Typically due to this security versus capacity trade-off, RAID 6 would usually only be employed in NAS appliances and servers where data critical.

Diagram showing RAID 6 configuration with dual parity protection

RAID 10

RAID 10 is referred to as a nested RAID configuration as it combines the protection of RAID 1 with the performance of RAID 0. Using four drives as an example, RAID 10 creates two RAID 1 arrays, and then combines them into a RAID 0 array. Such configurations offer exceptional data protection, allowing for two drives to fail across two RAID 1 segments. Additionally, due to the RAID 0 stripe, it provides users high performance when managing greater amounts of smaller files, so is often seen in database servers.

Diagram combining RAID 1 mirroring and RAID 0 striping across four drives

RAID 50

RAID 50 is referred to as a nested RAID configuration as it combines the parity protection of RAID 5 with the performance of RAID 0. Due to the speed of RAID 0 striping, RAID 50 improves upon RAID 5 performance, especially during writes, and also offers more protection than a single RAID level. RAID 50 is often employed in larger servers when you need improved fault tolerance, high capacity and fast write speeds. A minimum of six drives is required for a RAID 50 array, although the more drives in the array the longer it will take to initialise and rebuild data due to the large storage capacity.

Diagram showing RAID 50 nested configuration combining RAID 5 groups striped together

RAID 60

RAID 60 is referred to as a nested RAID configuration as it combines the double parity protection of RAID 6 with the performance of RAID 0. Due to the speed of RAID 0 striping, RAID 60 improves upon RAID 6 performance, especially during writes, and also offers more protection than a single RAID level. RAID 60 is often employed in larger server deployments when you need exceptional fault tolerance, high capacity and fast write speeds. A minimum of eight drives is required for a RAID 60 array, although the more drives in the array the longer it will take to initialise and rebuild data due to the large storage capacity.

Diagram showing RAID 60 nested configuration using RAID 6 groups striped together

What to look out for when choosing a NAS box

There are a few factors that determine the best type of NAS box to choose - these are to do with the physical shape and size as well as specific components, as detailed in the tabs below.

Form Factor

There are two common form factors of NAS box - desktop and rackmount. As the name suggests desktop NAS boxes simply sits on a desk or table top, whilst the rackmount type is designed to fit a standard 19in wide rack cabinet in a server room or datacentre. Rackmount NAS are usually higher specification devices as they are intended for much larger organisations, typically scaling to larger capacities and having more software features. Desktop NAS boxes usually top out at 12 drives bays while rackmount NAS models offer up to 24 bays.

It is also worth mentioning here that both types of NAS box 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.

Comparison image of desktop NAS and rackmount NAS enclosures

CPU

The CPU (Central Processing Unit) is the brain of any NAS, controlling how data is written to the drives and the speed at which it can be retrieved. A NAS device is designed to run 24/7, unlike a desktop PC or workstation, so even though a NAS CPU may appear modest, their focus is more about efficiency and minimal power consumption. NAS CPUs range from Arm-based Marvell, Annapurna or Realtek at the entry-level; Intel x86 models such as Intel Atom or Celeron at the mid-range; and Intel Xeon or AMD EPYC at the high-end.

Entry-level CPUs have the benefit of keeping the initial cost of the NAS device and its running costs low, however they may struggle with multiple concurrent users and they cannot handle transcoding, large-scale rendering or 4K media.

NAS processor illustration highlighting different CPU classes and performance levels

Memory

The amount of memory (or RAM) required in a NAS will largely depend on the applications and number of users accessing the NAS at any given time. A general a rule of thumb is that if your NAS is going to be used by more than five people and for backups and multimedia, then you should have at least 2GB RAM, or 4GB if you intend to use RAID. If, however, you are going to use a NAS for business, large-scale surveillance with multiple IP cameras for CCTV, or to run multiple VMs for users to have their own bespoke virtual desktop, then you will need to start with 16GB 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 would up to capacities such as 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.

RAM modules showing memory capacity considerations for NAS devices

Drive Bays

Although we’ve addressed CPU and RAM first, it is fair to say that the more drive bays a NAS box has then the specifications of the system will also increase in anticipation of heavier workloads, more users and more intensive applications. 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 remove a drive and replace it with a new one (either after failure or for upgrade), without the need to power down the NAS. Although RAID settings are required to effectively use this feature, it does make maintaining your data very simple. If you want these features then avoid entry-level NAS as they usually have fixed drive bays.

The majority of drive bays are 3.5in slots featuring SATA / SAS III connectors that will take either 3.5in or 2.5in HDDs or SSDs. Some NAS boxes also feature dedicated 2.5in drive bays aimed specifically at SSDs for caching data. A more recent development is the inclusion of multiple U.2 or M.2 NVMe SSD slots internally to enable tiered storage support in a single device being used for fast access and archive purposes.

NAS drive tray system demonstrating hot‑swappable HDD and SSD bays

Connectivity

NAS boxes include a variety of connections as standard. The very minimum every NAS device will have is an RJ45 Ethernet network connection - usually 1GbE. Some mid-range and high-end NAS boxes feature 10GbE, useful if you are working with larger multimedia files rather than simple documents. It is also common as NAS boxes increase in price and performance that multiple RJ45 Ethernet ports will be present, sometimes in mixed configurations such as 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 fail.

You may also see additional ports on a NAS device - USB ports at the front designed for direct upload of data from an external drive onto the NAS box, or at the rear for connection to an external storage drive to back up the NAS; eSATA ports enable simple expansion without loss of speed; and expansion ports provide connection to additional chassis or disk shelves for seamless scaling.

Image of Ethernet port used for NAS network connectivity USB
Image of USB port showing direct external storage connection capability Ethernet
Image of eSATA port for NAS expansion chassis connectivity eSATA
Rear panel showing proprietary NAS expansion ports for additional disk shelves Expansion Ports

Software

As we’ve touched on previously the basic functions of a NAS box are to store and share data, act as a backup and protect data. 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. These include management platforms; file syncing and encryption functions; data back-up, snapshotting and de-duplication capabilities; virtualisation and cloud integration features; surveillance, productivity and multimedia applications.

We previously mentioned that mid to high-end NAS devices are essentially small office servers and to this end some are equipped with the ability to connect and support many industry standard enterprise software environments from the likes of Microsoft, VMware and Citrix.

NAS software interface illustration representing management and application features

NAS‑optimised HDDs and SSDs

We’ve already mentioned that the 2.5in and 3.5in drive bays in a NAS box can support both HDDs and SSDs. While it is true that you can install any compatible HDD or SSD in NAS, this isn’t recommended as consumer-grade drives are designed for occasional use rather than the 24/7 use that is usually the case in NAS. Performance will suffer and the life span of the drives will shorten. To address this, leading drive manufacturers, WD and Seagate, have developed NAS‑optimised drives, specifically designed to be operated continuously.

The tabs below explore these NAS‑grade drives — it’s also worth mentioning that 3XS Systems can pre‑install any of these drives, so your entire NAS device is covered by a single warranty.

Seagate IronWolf HDDs

Seagate’s NAS‑specific drive line includes IronWolf for home, SOHO and small business NAS units up to 8 bays. IronWolf Pro is intended for businesses and creators who require higher performance and heavier workloads.

Seagate IronWolf HDD
Feature IronWolf IronWolf Pro
Capacity 1TB – 12TB 2TB – 32TB
Form Factor 3.5in 3.5in
Interface SATA 6Gb/s SATA 6Gb/s
Recommended Drive Bays 2–8 8–24
Spindle Speed Up to 7,200rpm 7,200rpm
Cache Up to 256MB Up to 512MB
Warranty 3yrs 5yrs

Seagate SkyHawk

Optimised for 24/7 surveillance workloads, SkyHawk drives include ImagePerfect firmware enabling smooth footage capture from up to 64 cameras. SkyHawk AI supports an additional 32 AI analytics streams.

Seagate SkyHawk HDD
Feature SkyHawk SkyHawk AI
Capacity 8TB – 24TB 2TB – 32TB
Form Factor 3.5in 3.5in
Interface SATA 6Gb/s SATA 6Gb/s
Recommended Drive Bays 2–8 8–24
Spindle Speed 5,400rpm 7,200rpm
Cache Up to 256MB Up to 512MB
Warranty 3yrs 5yrs

Seagate Exos

Enterprise‑class drives engineered for intensive workloads, high reliability and maximum areal density. Ideal for data centres, large business storage and high‑availability applications.

Seagate Exos HDD
Feature Exos
Capacity 600GB – 32TB
Form Factor 3.5in
Interface SATA 6Gb/s or SAS 12Gb/s
Recommended Drive Bays 8–24
Spindle Speed 7,200rpm
Cache Up to 512MB
Warranty 5yrs

WD Red Family

Designed for NAS workloads, WD Red Plus supports up to 8‑bay systems while WD Red Pro is built for larger 24‑bay arrays. Both offer quiet operation and anti‑vibration features.

WD Red HDD family
Feature WD Red Plus WD Red Pro
Capacity 1TB – 12TB 2TB – 24TB
Form Factor 3.5in 3.5in
Interface SATA 6Gb/s SATA 6Gb/s
Recommended Drive Bays 1–8 8–24
Spindle Speed Up to 7,200rpm 7,200rpm
Cache Up to 256MB Up to 512MB
Warranty 3yrs 5yrs

WD Purple

Engineered for surveillance and security systems. WD Purple supports continuous write workloads and smooth video streams, while Purple Pro Smart adds AI workload support.

WD Purple HDD
Feature WD Purple WD Purple Pro Smart
Capacity 1TB – 14TB 8TB – 26TB
Form Factor 3.5in 3.5in
Interface SATA 6Gb/s SATA 6Gb/s
Recommended Drive Bays 1–8 8–24
Spindle Speed Up to 7,200rpm 7,200rpm
Cache Up to 512MB 512MB
Warranty 3yrs 3yrs

WD Gold

Built for enterprise environments, WD Gold HDDs deliver maximum reliability, endurance and performance for mission‑critical deployments.

WD Gold HDD
Feature WD Gold
Capacity 1TB – 26TB
Form Factor 3.5in
Interface SATA 6Gb/s
Recommended Drive Bays 8–24
Spindle Speed 7,200rpm
Cache 512MB
Warranty 5yrs

Seagate BarraCuda SSDs

Ideal for personal NAS storage, BarraCuda SSDs offer high‑speed data access and efficient performance for general usage and creative workflows.

Seagate BarraCuda SSD
Feature BarraCuda SATA BarraCuda M.2
Capacity 240GB – 4TB 512GB – 4TB
Form Factor 2.5in M.2 2280
Interface SATA 6Gb/s NVMe
Recommended Drive Bays 1–24 M.2 slots
Warranty 5yrs 5yrs

Seagate Nytro SSDs

Nytro SSDs are engineered for enterprise and datacentre usage, offering exceptional endurance, speed and reliability for mission‑critical workloads.

Seagate Nytro SSD
Feature Nytro SATA Nytro M.2
Capacity 400GB – 15TB 480GB – 2TB
Form Factor 2.5in M.2 2280
Interface SATA 6Gb/s NVMe
Recommended Drive Bays 1–24 M.2 slots
Warranty 5yrs 5yrs

WD Red SSDs

WD Red SSDs are designed for 24/7 NAS workloads, combining durability with caching and accelerated performance for multimedia, databases and multi‑user environments.

WD Red SSD family
Feature WD Red SATA WD Red M.2 SATA WD Red M.2 NVMe
Capacity 500GB – 4TB 500GB – 2TB 250GB – 4TB
Form Factor 2.5in M.2 2280 M.2 2280
Interface SATA 6Gb/s SATA 6Gb/s NVMe
Recommended Drive Bays 1–24 M.2 slots M.2 slots
Warranty 5yrs 5yrs 5yrs

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. If you need access to mission critical data then a larger NAS array with smaller individual drives may be the better option.

Visual example showing a 4‑drive NAS using 8TB drives with slower rebuild times

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

Visual example showing an 8‑drive NAS using 4TB drives with faster 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.

M.2 SSD and 10GbE combo expansion card for NAS devices

M.2 SSD / 10GbE Combo Card

Additional view of M.2 SSD and 10GbE expansion card for NAS systems

M.2 SSD / 10GbE Combo Card

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:

NAS add‑in card supporting M.2 NVMe SSDs for caching or tiered storage

M.2 SSD / 10GbE Combo Card

M.2 NVMe SSD add‑in card for high‑speed NAS acceleration

M.2 NVMe SSD Card

M.2 SATA SSD add‑in card for NAS storage expansion

M.2 SATA SSD Card

Dual 10GbE network card for high‑speed NAS connectivity

2x 10GbE Card

Dual SFP+ 10GbE fibre network card for NAS systems

2x SFP+ 10GbE Card

SAS expansion card enabling connection to external drive shelves

SAS Expansion Card

Ready to Buy?

Browse our selection of HDDs to find the perfect fit for your setup.

Desktop NAS Prepopulated desktop NAS Rackmount NAS Prepopulated rackmount NAS NAS HDDs NAS accessories
Selection of NAS devices and drives ready to purchase

Frequently Asked Questions FAQ

Here are some common questions and answers to help you find the information you need.

A NAS (Network Attached Storage) is a dedicated device that connects to your network, providing centralised, accessible storage for multiple users and devices, essentially acting as a private cloud for backups, file sharing, media streaming, and data management, often using RAID for data protection.

An SSD (Solid State Drive) is a storage device that uses flash memory to store data, unlike older Hard Disk Drives (HDDs) that use spinning platters.

As SSDs have no moving parts, they are significantly faster, more durable, quieter, and more power-efficient, making them the standard for modern computers to boot up quickly and run applications smoothly.

An HDD (Hard Disk Drive) is a traditional, electro-mechanical data storage device that uses rapidly spinning magnetic platters and read/write heads to store and retrieve digital information.

You should use an HDD primarily for cost-effective, massive data storage, backups or archives; where the speed advantages of SSDs have little impact.

SSDs use flash memory for much faster speeds, durability, and less power, while HDDs use spinning magnetic platters, making them cheaper for large storage but slower and more fragile.

A NAS SSD or HDD is a high-endurance, highly reliable drive built for NAS environments, offering higher reliability for the 24\7 use of NAS boxes compared to consumer SSDs and HDDs designed for personal computers.

RAID (Redundant Array of Independent Disks) is a data storage technology that combines multiple physical drives (HDDs or SSDs) into a single logical unit for improved performance, data redundancy, or both, appearing as one drive to the system.

RAID should be primarily used for improved data reliability (redundancy) and faster performance (speed) by combining multiple drives, making systems more fault-tolerant and efficient for demanding applications.

No, although RAID helps protect data by spreading it across multiple disk drives, backing-up data onto a completely separate device is still advised.