External storage may be used alongside internal storage (HDDs or SSDs) to add extra capacity, share data, or back it up. There are a number of ways that external storage devices connect to your computer, each with a distinct set of advantages and use cases, as explained in the tabs below.
Additional storage can be added easily by connecting an external enclosure with one or more additional drives in it. The enclosure may be temporarily or permanently connected to the computer, and used for adding to the internal storage or for protecting sensitive files if the external storage has multiple drives.
A network router connects devices together by either wired connection or wireless technology. By storing data on a network-connected enclosure, it allows multiple users to access it either locally or remotely. Usually Network Attached Storage (NAS) devices have multiple drives in them, as the intended purpose is not only sharing but adding data protection too.
Internal storage is just one element of a computer system, whether PC, laptop or server. In many cases the internal storage provided is adequate to match the other components, such as CPU or GPU. In cases where storage is required to provide specific high performance, internal storage may be largely ignored in favour of specialised, dedicated shared storage.
Critical data should always be backed up, and external storage is a way to achieve this. Due to the dedicated nature of backup storage, security can also be enhanced by using multiple drives to increase integrity. External backup storage can then be replicated in a second location if required, for additional protection.
Additional storage can be added easily by connecting an external enclosure with one or more additional drives in it. The enclosure may be temporarily or permanently connected to the computer, and used for adding to the internal storage or for protecting sensitive files if the external storage has multiple drives.
Although we talk about these two types of storage as opposing approaches, they are truly complementary. There will always be a need for both, even if one is heavily favoured over the other - below are a few example scenarios to illustrate how they function together, but not always equally.
A family may use multiple PCs, laptops and smartphones - all with their own internal storage. However, there may be a need to bring together photos and videos from each family member into one place where they can be safeguarded and shared, whether at home or away. An external storage device connected to the network router allows exactly this, plus it creates a backup should a smartphone or laptop be lost or stolen.
Self-employed workers may take their laptop with them to client sites, so portability is key, but a light laptop will contain limited storage capacity. An external storage drive at home allows you to offload critical data by connecting it as and when required. This external enclosure could contain multiple drives for extra capacity, data protection or both - connect it to the router and it can be accessed while out and about too.
The more data a business has, the more critical it is that it is protected. Typically, employees' machines will have limited internal storage (OS only) and centralised storage is used instead. Dedicated storage appliances store and manage data intelligently according to access need or file type, where it is also cleansed, protected and backed up automatically - either locally, to another site, or the cloud.
Where high performance compute is being deployed, similarly high performance dedicated storage is needed to provide data transfer rapidly enough to match server capability. In these cases, external storage appliances are likely to be software-defined and specifically tailored for optimum performance in specific workloads.
It is fair to say that at the most basic level external storage works the same way as internal storage does - in that data is ultimately stored on either HDDs or SSDs. You can learn much more about the types and sizes of HDDs and SSDs available, their characteristics, interfaces and ideal usage scenarios by reading our dedicated HDD Buyers Guide and SSD Buyers Guide.
The table below offers a simple comparison between the two technologies, highlighting how they differ and the potential advantages and disadvantages of each.
| Characteristic | HDD | SSD | Comparison |
|---|---|---|---|
| Performance | Hundreds of MB/sec | Thousands of MB/sec | SSDs are much faster |
| Access Times | 5-8ms | 0.1ms | SSDs have almost no latency |
| Reliability | 2-5% failure rate | 0.5% failure rate | SSDs are much more reliable |
| Resilience | Susceptible to vibrations | No moving parts | SSDs are much safer to install in external storage |
| Energy Use | 6-15W | 2-5W | SSDs are much more energy efficient |
| Noise | 20-40dB | Silent | No noise from SSD |
| Capacity | Up to 26TB | Up to 26TB | Similar in maximum capacities |
| Cost | £-££ | ££-££££ | SSDs are more expensive, especially at high capacities |
| Although SSDs prove favourable in almost every comparison above, some of these parameters are not as straightforward when it comes to external rather than internal storage. For example, noise is less important if an external storage device is housed in a datacentre, and the lower cost of HDDs may prove a better choice for archiving data. | |||
There are various types of external storage devices that differ from each other in their features, uses, advantages and disadvantages and relative cost. The table below summarises these differences, which are then explored in more detail in the tabs.
| Type | DAS | NAS | JBOD | Software Defined Storage | AI-Optimised | Tape |
|---|---|---|---|---|---|---|
| Home Use | ✔ | ✔ | ✖ | ✖ | ✖ | ✖ |
| Solo or Shared Use | Solo | Shared | Shared | Shared | Shared | Shared |
| Business Use | ✖ | ✔ | ✔ | ✔ | ✔ | ✔ |
| Archiving Use | ✖ | ✔ | ✖ | ✔ | ✖ | ✔ |
| Performance | Medium | Medium* | Slow* | High* | High* | Very Slow |
| Capacity | Low | Medium | High | High | High | High |
| Portable | ✔ | ✖ | ✖ | ✖ | ✖ | ✔ |
| Data Protection (RAID etc) | ✖ | ✔ | ✖ | ✔ | ✔ | ✖ |
| Cost | £ | ££ | £££ | ££££ | £££££ | ££ |
| * performance is also dependent on network speed. | ||||||
Direct Attached Storage (DAS) refers to external storage devices that are directly connected to a computer system - most typically a standalone PC, workstation or laptop - by means of a USB-A, USB-C or Thunderbolt port. DAS devices can be permanently connected to provide additional storage (desktop drives) or temporarily connected to offload or back up data (portable drives). It is advisable to check the type of ports your computer has and that the drive is Windows or Mac compatible too. A portable external drive will be a sealed unit, whereas for desktop versions you have the option of buying a pre-populated model with a drive already installed, or an empty external enclosure for you to add a drive into.
Network Attached Storage (NAS) refers to an external storage device that is connected to a network rather than directly to a computer. The main advantage of this is the ability to share access to the data, allowing multiple users to connect via the network whether in the same building as the NAS device or outside, over the internet. There are two common form factors of NAS - desktop and rackmount. As the name suggests, desktop boxes simply sit on a desk or table top in the home or in a small office, and have a cable connecting them to the network.
The rackmount type is designed to fit a standard 19in wide computer rack cabinet in a server, comms room or datacentre. As you may expect, the rackmount type are usually higher specification devices, as they are intended for much larger organisations. NAS devices also benefit from RAID protection (see below), enabling data to be protected in the case of drive failure. You can learn more about NAS solutions by reading our NAS Buyers Guide.
Just A Bunch Of Disks (JBOD) refers to an external storage device that is connected to a network rather than directly to a computer. The main advantage of this is the ability to share access to the data, allowing multiple users to connect via the network whether in the same building as the JBOD or outside, over the internet. There are two common form factors of JBOD - desktop and rackmount. As the name suggests, desktop boxes simply sit on a desk or table top in the home or small office, and have a cable connecting them to the network.
The rackmount type is designed to fit a standard 19in wide computer rack cabinet in a server, comms room or datacentre. As you may expect, the rackmount type are usually higher specification devices, as they are intended for much larger organisations. A JBOD is very similar to a NAS, however, as the 'Just a Bunch of Disks' name suggests, there are no RAID protection features (see below), so although costs may be less and no data capacity is lost to RAID functionality, any drive failure will certainly result in loss of data.
Software Defined Storage (SDS) refers to complete data management systems, offering scalability, protection, compression, cloud integration and much more. Solutions like these are built by dedicated server or storage manufacturers such as Dell, DDN and NetApp. This type of storage is often referred to as tiered, as a single system can be used for data that needs to be accessed all the time (hot), data that is regularly accessed (warm), and data that is archived (cold). Additional disk shelves may contain different drive types - the fastest NVMe SSDs for hot data, SATA SSDs for warm data and HDDs for cold data - with the software dynamically moving data between these layers as it is accessed, to increase efficiency while simultaneously performing compression and de-duplication.
This is a development of SDS where the software has been optimised for specialised deep learning and AI workflows. Today's AI servers consume and analyse data at much higher rates than many traditional storage solutions can deliver, resulting in low GPU utilisation and dramatically extending training times. PEAK:AIO has developed a software platform from the ground up for AI workloads, optimised for use with NVIDIA DGX, HGX, EGX and MGX AI servers, delivering ultra-low latency and tremendous bandwidth at a price which allows more investment to be made on GPU resource and less on legacy storage. Learn more about PEAK:AIO Storage and PEAK:AIO Archive solutions.
Tape storage is an older external storage solution that differs from the rest listed here, in that it uses magnetic tapes and a tape drive to read and write data, rather than HDDs or SSDs. Although many organisations have switched to disk or cloud for backup purposes, tape technology is still widely used for backup and recovery, even where intelligent NAS or SDS solutions are employed for data efficiency and protection in the first instance. This is because backing up data using HDDs, SSDs or cloud storage isn't practical, as the cost quickly spirals out of control - even the best server HDDs and SSDs only have a six-year warranty. In contrast, despite its slow performance, tape remains the best format for backup, as it offers a much lower cost per terabyte and most tapes are rated for up to 30 years. Learn more in our Tape Backup Buyers Guide.
When considering a multi-drive external storage solution - whether DAS, NAS or SDS based - it is vital to understand how best to protect the data on your drives. This can be achieved using RAID technology. RAID stands for Redundant Array of Independent Disks, and it works by spreading data over multiple drives to remove the chance of a single point of failure. Blocks of data, referred to as parity blocks, are distributed across multiple drives so that, in the event of a drive failure, 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 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 a RAID 0 configuration may be ideal for gaming, where performance matters but data is not important, it is not recommended for storing critical data.
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.
RAID 5 writes data across all drives in the array, plus a parity block for each data block. If one drive fails, the data 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 usable storage due to the parity blocks - for example, if four 2TB drives were employed, the usable capacity would be 3 x 2TB = 6TB. Although some capacity is lost, performance is almost as good as RAID 0, so RAID 5 is often seen as the sweet spot for many workstation and NAS uses.
RAID 6 writes data across all drives in the array, like RAID 5, but with two parity blocks for each data block. This means two drives can fail without loss of data, as it can be rebuilt onto replacement drives. A minimum of four drives is required, although due to the dual parity block, two drives' worth of capacity is lost - for example, five 2TB drives would give a usable capacity of 3 x 2TB = 6TB. Due to this security-versus-capacity trade-off, RAID 6 is usually only employed in NAS appliances and servers with critical data.
RAID 10 is 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 high performance when managing greater amounts of smaller files, so it is often seen in database servers.
RAID 50 is 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 on RAID 5 performance, especially during writes, and offers more protection than a single RAID level. RAID 50 is often employed in larger servers when improved fault tolerance, high capacity and fast write speeds are needed. A minimum of six drives is required, although the more drives in the array, the longer it will take to initialise and rebuild due to the large storage capacity.
RAID 60 is 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 on RAID 6 performance, especially during writes, and offers more protection than a single RAID level. RAID 60 is often employed in larger server deployments when exceptional fault tolerance, high capacity and fast write speeds are needed. A minimum of eight drives is required, although the more drives in the array, the longer it will take to initialise and rebuild due to the large storage capacity.
Systems that support RAID arrays will usually have a hot-swap capability, meaning a failed drive can be removed from the array without powering the system down. A new drive is put in the failed drive's place, and the array rebuild begins automatically. You can also configure a hot spare drive - an empty drive that sits in the array doing nothing until a drive fails, meaning the rebuild can start without the failed drive being removed first. Multiple RAID arrays can also be configured in a single system - for example, RAID 1 protecting a pair of SSDs for the OS, while multiple HDDs are protected by RAID 5.
Ultimately, the RAID configurations you choose need to be controlled - for desktop PCs and workstations this is usually handled at the CPU chipset or software level, as basic controller features are built into many Intel or AMD motherboards and operating systems such as Microsoft Windows. For more complicated systems, a hardware controller may be required - read more in our Storage Controller Buyers Guide.
Throughout this guide we've touched on how external drives connect to the PC, workstation, laptop or server. There is a wide range of options, including USB, Thunderbolt, wireless, Ethernet and InfiniBand - each with their own sweet spots and use cases.
The most popular interface for DAS devices. Transfer speeds range from 5Gb/s (USB 3.0) up to 80Gb/s (USB4 2.0).
Thunderbolt is a technology based on the USB-C port but it has the ability to transfer video as well as data. It is used extensively in the Apple Mac ecosystem using the same ports to connect external storage devices, monitors and more. The latest generation has a maximum transfer speed of 80Gb/s.
Few external storage devices are wirelessly enabled, but NAS devices connected to a wireless router can be accessed this way, with speeds dependent on the router and signal.
By far the most common network connection for external storage, used in all types of NAS and SDS systems, ranging from 1Gb/s up to 800Gb/s for high-end systems.
An alternative network technology to Ethernet, deployed for demanding applications where high bandwidth and low latency are key. Scales up to 800Gb/s at the high end.
It may seem strange to only talk about storage capacity at the end of this guide, as it may seem one of the most obvious questions to ask - what size storage do you need? However, having covered the various types of devices and their features, you'll see there are numerous factors that will decide how the capacity you choose will be used up. The scenarios below may help guide the decisions you should consider.
A home user may start with an idea that they need 2TB of external storage, having added up the photo sizes across their various computers and smartphones. On top of this basic requirement, they should consider how long it took to accumulate that 2TB, and whether their current devices take higher-resolution photos than their previous ones, resulting in larger file sizes going forward. If they have 2TB now, then 4TB allows room to grow. If they want to protect their valuable memories, a twin-drive RAID-capable DAS or NAS may be best, so 2x 4TB becomes 8TB. It is far better value in terms of time and money to get the right solution first time, rather than realising your chosen device isn't big enough very quickly.
A business organisation will face the same issues, but as most rackmount storage arrays can be partially populated at purchase, expansion can be handled as demand grows. It is worth considering the type of drives you use - you could start with a 12-bay NAS and populate 4x 12TB drives, giving 48TB of space. In RAID 5 you will lose one drive's capacity, resulting in 36TB usable space. Should a drive fail, rebuilding a 12TB chunk of data will take considerable time, so it may be better to choose 8x 6TB drives to achieve your 48TB in RAID 5 - not only will a 6TB rebuild take much less time, you will also realise 42TB usable space, as you only lose 6TB for parity. If you are using more than four HDDs in an enclosure, you should always choose NAS- or enterprise-grade drives, as these are designed for 24/7 runtime and have built-in vibration resistance to extend the life of the drive.
Although higher-end NAS and SDS systems are designed with scalability in mind, capacity is less of a concern at the point of purchase - it becomes more of a consideration when using one or several data management features. As mentioned, RAID reduces usable capacity, whereas compression and de-duplication act to increase usable space. If you are operating tiered storage, you may compress and de-duplicate at the cold layer, only de-duplicate at the warm layer, and leave the hot layer untouched for fastest access. When calculating initial capacity or adding extra drives, the type of drive and its intended layer location will impact your calculations.
Should your chosen external storage be either NAS, SDS or AI-optimised, there are further considerations that pertain to the wider infrastructure including compatibilities with servers, networking switches and UPS protection. You can learn more by reading our Servers Buyers Guide, Network Card Buyers Guide, Network Switch Buyers Guide and UPS Buyers Guide.
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A few common questions to help you choose the right external storage solution.
External storage refers to any storage device connected to rather than contained within a PC, laptop, workstation or server.
DAS (Direct Attached Storage) refers to external storage devices that are directly connected to a computer system - most typically a standalone PC, workstation or laptop - by means of USB-A, USB-C or Thunderbolt port, rather than across a network.
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 persistently, 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 lower power consumption, while HDDs use spinning magnetic platters, making them cheaper for large-capacity storage but slower and more fragile.
A datacentre or enterprise SSD or HDD is a high-endurance, highly reliable drive designed for enterprise environments, offering consistent performance, power-loss protection and robust data integrity for 24/7 mission-critical operations.
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.
RAID should be primarily used for improved data reliability (redundancy) and faster performance 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 drives, backing up data onto a completely separate device is still advised.