External Storage Buyers Guide

What is External Storage?

External storage refers to an entire family of products that act as data storage outside of your PC, laptop, workstation or server. External storage may be used alongside internal storage (HDDs or SSDs) to add extra capacity, share and backup data.

There are a number of ways that external storage devices connect to the computers, each with a distinct set of advantages and use cases. In this guide we’ll look at all types of external storage - USB, Thunderbolt, NAS, JBOD, SDS, AI optimised and Tape - why you should consider them and what they are best used for, so you are sure to make the best decisions when choosing a product.

Why Use External Storage?

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 ether 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.

Internal storage is just one element of a computer system whether PC, laptop or server. In many cases the internal storage provided or that can be specified is adequate to match the other components such as CPU or GPU. In cases where the storage is required to provide specific high performance, the 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. However due to the dedicated nature of backup storage the security of the backed-up data can also be enhanced by using multiple drives to increase integrity. External backup storage can then be replicated in a second location if required to add additional protection.

Any computer device may contain fast internal storage to access files needed regularly, or fast dedicated high performance storage may be added if high capacities are required. However, where files are needed to be archived separate external storage can be a cost-effective way to do this by employing low cost HDDs to house data that must be kept but very rarely accessed.

Internal vs External Storage

Although we talk about these two types of storage as opposing approaches they are truly complimentary. 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.

For the Home

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 family members to upload their photos to it - this creates a back-up should a smartphone or laptop be lost or stolen. It also allows viewing of photo or video files on a network connected smart TV, a much larger screen than any of the individual devices.

For the Home Office

A self-employed worker may take their laptop with them to client sites or locations such as building sites, so portability is key and a light laptop may contain limited storage capacity. An external storage drive at home allows them 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 at work too.

For the Large Organisation

The more data a business or organisation has, the more critical is it that it is protected. Typically employees’ machines will have limited internal storage (OS only) and centralised storage is used. This will also apply at a server level, as the devices providing email and website functions for a company may only contain the compute power to do so and storage be handled by dedicated storage appliances where data can be stored intelligently according to access need or file type, and cleansed, protected and backed-up automatically - either locally, to another site or the cloud.

For the Research Organisation

Where high performance compute is required, dedicated storage is needed to provide data fast enough to match server capability. In these cases external storage appliance are always used as the drive technology can be tailored to meet the demands. In these scenarios data will be uploaded to external as required so the owness is not on data protection or necessarily large capacity - just performance - so the external devices are likely to be optimised for their usage without unneeded functionality.

How External Storage Works

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 stored on either a hard disk drive (HDD) or a solid state drive (SSD). Data is written digitally in the form of ones and zeros (called bits), and so any storage device must have the ability to create these two digital states and then read the patterns they create (e.g. 100011 vs. 110001). Eight of these bits make up a byte - a unit of digital information - and it is these bytes that define the capacity of a drive, usually given in GB (gigabytes) or TB (terabytes). All the most common capacity parameters within are computing are discussed in terms of bytes - kilobytes (KB - 1000 bytes), megabytes (MB - 1000 kilobytes), gigabytes (GB - 1000 megabytes), terabytes (TB - 1000 gigabytes), petabytes (PB - 1000 terabytes) and so on.

Hard Disk Drives (HDDs)

Solid State Drives (SSDs)
An HDD contains one or more spinning disks called platters. These platters have thousands of tiny segments, with the ability to be individually magnetised (1) or demagnetised (0). It is the sequence of magnetised or demagnetised sections that define bytes of data. The magnetisation state of the drive segments is physically changed by an arm that passes over the platter and ‘writes’ the bytes of data to a section of it. Once data is stored on the disk platter by way of magnetisation it will remain in this state even when the power is off and the disk stops spinning, until it is either written over with new data or deleted altogether.

The data is written in a logical fashion so it can easily be found and ‘read’ by the arm too. You’ll also see from the diagram above that there are multiple platters and arms to write to them or read from them. This is how the capacity of the hard drive is configured. Over time HDDs have seen the capacity of a single platter increase and the number of platters increase resulting in larger and larger drive capacities. As an HDD capacity gets larger there may be greater latency in retrieving data from it, as the arms physically have to trace a larger area of bytes distributed over multiple platters. For HDDs that are designed for ‘enterprise’ use - within a server storing mission critical data - the spinning speed of the platters is increased to help mitigate this latency by finding the data faster. Enterprise rated drives may be listed as 10,000rpm or 15,000rpm as opposed to regular PC HDDs at 7200rpm and laptop HDDs at 5400rpm.
An SSD uses semiconductor chips to store data rather than magnetic media like an HDD and is termed solid state because there are no moving parts within the drive. Like an HDD though, the data stored is kept in place when there is no power to the drive, so the ultimate result of data retention is the same. However, that is where the similarity ends. Instead of spinning disks the internal space is taken up by memory chips called NAND. As writing and reading from NAND doesn’t require a physical arm to access the data like in an HDD, the data access speeds are much faster.

NAND is made up of transistors in columns and rows which can either conduct current (1) or don’t conduct current (0). When precise voltages are applied to the network of transistors (called cells) a pattern of 1s and 0s is formed to represent the data. NAND memory comes in several types based on how many 1s and 0s can be stored in each cell. Single-Level Cell (SLC) NAND stores one bit - either a 1 or a 0 - per cell, whereas Multi-Level Cell (MLC) NAND stores two bits per cell. Triple-Level Cell (TLC) NAND stores three bits per cell and Quad-Level (QLC) NAND stores, you guessed it, four bits per cell. Each of these types offer differences in maximum capacity, longevity, reliability and cost. Although an SSD contains no moving parts to fatigue, the cells within NAND do wear out through repeated Program (writing) / Erasing (P/E) cycles, although the drive controller will work to spread data evenly across the cells to create consistent wear across the whole capacity.

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, SSD buyers Guide. If you are concerned with drives for servers or high-end storage then please read our Enterprise Storage Drive Buyers Guide.

The below table offers a simple comparison between the two technologies, highlighting how they differ and the potential advantages / disadvantages of each:

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 much more reliable
Resilience Susceptible to vibrations No moving parts SSD much safer to install in a laptop
Energy Use 6-15W 2-5W SSD much more energy efficient
Noise 20-40dB Silent No noise from SSD
Capacity Up to 26TB Up to 26TB Similar in maximum capacities
Cost £-££ ££ - ££££ SSD more expensive, especially at high capacities

Although the table clearly shows that SSDs prove to be favourable in almost every comparison when compared to HDDs, however some of these parameters are not as straight-forward when it comes to external rather than internal storage. For example, the latency may be minimal in SSDs however if used in a network connected storage device, factors such as network speed and volume of other network traffic will affect data access times much more than the latency of the SSD itself. Similarly noise is less important if an external storage device is housed in a data centre and the lower cost of HDDs may prove a better choice for archiving data. We’ll cover these considerations in more detail later in this guide, when we consider each type of external storage device in more depth.

Types of External Storage Devices

In this section we’ll look at the various types of external storage devices that are available and how they differ from each other. We’ll focus on their features, uses, advantages and disadvantages and show their relative cost.

USB / Thunderbolt

This type of storage is sometimes referred to as DAS or Direct Attached Storage and covers external storage devices that are directly connected to the computer system they are used by - most typically a standalone PC, workstation or laptop - by means of USB-A, USB-C or Thunderbolt port. DAS devices can be permanently connected to provide additional storage or temporarily connected to offload data or backup data. It is advisable to check the type of ports your device has and that the drive is Windows or Mac compatible too.


Portable Drives

A portable external drive is designed for mobility, so usually smaller with lower capacities. They can feature an HDD or an SSD, the latter having the advantage of no moving parts so less sensitive to damage when being moved. Portable drives are host-powered - meaning no dedicated power supply is required - it receives its power from the port it is connected to.


Desktop Drives

A desktop external drive is typically larger in size and capacity than an external portable drive. It will also have a power supply and require its own plug socket. Again, it can feature either an HDD or an SSD - an HDD may be larger capacity and cost less, however an SSD version will be much faster and quieter.


Large Capacity Drives

A desktop external device with multiple drives functions the same way as those with just a single drive, however the included software will allow to you set up RAID levels to protect your data against drive failures, more on this later. Again, you may have a choice of HDDs or SSDs affecting cost, access speeds and noise.

It is worth noting that a portable external drive will be a sealed unit, whereas for desktop versions you have the option of buying a prepopulated model with a drive already installed, or an empty external enclosure for you to add a drive into. Empty enclosures come in a variety of types with varying internal interfaces in order to offer a choice of what drive to install.


Network Attached Storage (NAS) refers to external storage where the device is connected to a network router rather than directly to a PC, workstation or laptop. As we’ve touched on, the main advantage of this is the ability to share access to the data, allowing multiple users to connect via the router whether in the same building as the NAS unit or outside, over the Internet. NAS boxes are usually larger capacity than DAS drives, due to them being designed for sharing - you can get single and twin drive NAS units but these are limited to either no or only basic RAID protection (0 or 1). More commonly shared data would usually be quite valuable so four drives is often the starting point for these units as this allows more advanced RAID 5 configurations to protect data in the event of drive failure, yet minimises lost capacity due to parity.

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 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, coms room or datacentre. 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 more software features. Desktop NAS boxes usually top out at 12 drives bays while rackmount NAX boxes models offer up to 24 bays.

Most NAS boxes feature hot-swap drive bays allowing any drive to be taken out and swapped for another without powering down the whole unit. This feature allows drives to be added to increase capacity - either into empty bays or replacing existing smaller capacity drives. It is also key in reducing recovery times when a drive fails and the drive array needs to be rebuilt. A JBOD (Just a Bunch of Disks) is essentially a NAS device that without any RAID protection - they are designed for maximum capacity and often seen in archive systems where the data may be less critical.

You can learn much more about NAS devices, their capabilities and the specialised NAS internal drives we recommend installing, by reading our dedicated NAS Buyers Guide.

Software Defined Storage

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 DDN, Dell and NetApp. An enterprise storage system like this will usually have a head unit which contains some drives and two redundant controllers that use a software platform to oversee how data is written across the head unit and associated disk shelves.

This type of storage is often referred 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 traditional HDDs for cold data - and the software will dynamically move data between these layers or pools, as it is accessed less or more to increase the efficiency of the system. The hardware can also be integrated with a cloud provider such as AWS or GCP, allowing data to be taken from the cold layer and moved to the cloud for better cost-effectiveness.

SDS systems include all the RAID protection configuration options that we’ve covered, plus often a more advanced setting known as Erasure Coding (EC). Erasure Coding is also parity-based - like RAID - which means the data is broken into fragments and encoded, so it can be stored anywhere, but it uses less storage capacity than RAID, and allows for data recovery if two or more parts of a storage system fail. This means rebuild times are much faster, so is ideally suited to SDS systems where vast drive capacity is common across the various disk layers and the cloud.

SDS systems are usually much more feature rich than other external storage solutions as they comprehensively manage the data - alongside dynamic provisioning you will usually find a huge range of others functions including the following:

As the name suggests, compression means compacting the data so that it consumes less space. All data created has some supporting information on it and a lot of spaces and other allied fillers on it and every bit of this consumes space on the storage device. Compression helps compact this data by removing the unnecessary fillers and spaces in the data, while retaining the vital pieces of information without compromising on data losses.

When data is uploaded to a storage system it may have come from multiple sources and may contain common parameters - this repeated information takes up space. Deduplication compiles all the repeated data and replaces it with a hash number or a pointer. Additionally, deduplication saves only one copy of the data with the hash number or pointer pointing towards the single copy, so when you need to access the data, it can be quickly done. This also does not lose any critical information within it.

When data is uploaded to a storage system it may have come from multiple sources and may contain common parameters - this repeated information takes up space. Deduplication compiles all the repeated data and replaces it with a hash number or a pointer. Additionally, deduplication saves only one copy of the data with the hash number or pointer pointing towards the single copy, so when you need to access the data, it can be quickly done. This also does not lose any critical information within it.

AI Optimised Storage

This is a development of SDS where the software levels has been entirely 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, decreasing productivity. PEAK:AIO has developed a software platform from the ground up for AI workloads and optimised for the NVIDIA DGX, HGX and EGX range of AI appliances. 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 - ensuring your project’s funds are better spent and your team is more productive. PEAK:AIO is designed for direct connection to GPU servers or small to mid-size clusters of up 10 GPU servers via InfiniBand or Ethernet switches.

GPU-ready performance

Using the GPUDirect and RDMA protocols AI data servers powered by PEAK:AIO can deliver over 80GB/s to GPU servers.

Evolved file system and features

Using the industry-standard NFS3/4 protocols PEAK:AIO data servers are simple to connect and don’t require any complex drivers.

Fault Tolerance and Flexible Features

PEAK:AIO dispenses with the features that slow down legacy storage solutions, but retains RAID protection for your data.


As your AI projects evolve PEAK:AIO AI data servers grow alongside, scaling in capacity from as little as 30TB to up to 720TB per 2U.

Cost Effective

PEAK:AIO AI data servers are much more cost-effective than legacy storage, enabling you to spend more on GPU servers.

You can learn more about AI optimised storage by visiting our dedicated PEAK:AIO page.

Tape Storage

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 / 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 purposes, even if intelligent NAS or SDS solutions are employed for data efficiency and protection in the first instance. Backing up data using HDDs and SSDs or cloud storage isn’t practical as the cost quickly spirals out of control. In addition, even the best server HDDs and SSDs only have six-year warranty. In contrast, despite its slow performance, tape remains the best format for backup as it offers much lower cost per terabyte and most tapes are typically rated for up to 30 years.

Tape is a much older technology and works differently to HDDs and SSDs in that it must be sequentially written and read - meaning you can only write to blank sections that follow already written sections and you can only read one section by reading the others before it - later generations use LTFS (Linear Tape File System) to improve access. Although magnetic tape media may seem old and clunky next to HDDs, SSDs and the cloud, it does have numerous advantages that make it ideal for back. Firstly, once data is written to the tape it is usually removed from the drive making it un-hackable. Even archive HDD and SSD systems, whether on-premise or in the cloud need to be connected to a network so they vulnerable. Secondly, tapes are much cheaper than cloud storage SSDs and in many cases HDDs, so prove very cost-effective for keeping a copy of critical data with minimal overhead cost and risk. You can learn more about tape technology by reading our dedicated Tape Back-up Buyers Guide.

External Storage Connectivity

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. Let’s take a closer look.



USB 3.0 or USB-C are the most popular interfaces for DAS devices - designed to be connected directly to the USB ports of a laptop, PC or workstation. Transfer speeds are up to 5Gb/s (USB 3.0) or 20Gb/s (USB-C). 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, power supplies and more. It has a maximum transfer speed of 40Gb/s. Although there are very few wirelessly enabled external storage devices, it may be common to access a NAS device connected to a wireless router. In this case the access speeds will be determined by the wireless standard, other wireless traffic, interference, signal strength and distance from the router.


Ethernet is by far the most common connection for external storage used in all types of NAS and SDS systems. Basic systems may feature 1 or 10 GB/s speeds ranging up to 40, 50, 100, 200 and 400Gb/s speeds for high end systems. These latest speeds of Ethernet now feature CPU off-loading similar to Infiniband making the two technologies very similar nowadays. Standard Ethernet speeds use an RJ45 port, whereas the higher speeds use SFP or QSFP ports. InfiniBand is an alternative technology to Ethernet, usually found with demanding applications where high bandwidth and low latency are key requirements. Infiniband has achieved improved throughput by not needing to use the server CPU to control data transmission, hence latency is reduced by removing this step. The common speeds are Enhanced Data Rate (EDR - 25Gbps), High Data Rate (HDR - 50Gbps), and the fastest Next Data Rate (NDR - 100Gbps). Specific 4x cables then increase maximum throughputs to 400Gb/s. All these standards utilise SFP or QSFP ports.

All these connectivity methods require both the host and storage device to have matching ports and standards to maximise speed and bandwidth. For example, a USB 3.0 DAS drive connected to an older USB 2.0 port on a PC will step down to the USB 2.0 transfer speeds. Similarly, the NDR network ports in an SDS appliance will not transmit at maximum speed if connected to a server limited to EDR speeds. To add to this, in most real-world cases in a business environment it is more likely that servers and external storage devices are connected by network switches to allow access to all users. In this case the switch ports also need to be of the same capabilities - speed / standard - to ensure bottlenecks are created. You can read more about these networking standards and networking by reading our Network Switch Buyers Guide.

External Storage Capacity

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. Let’s look at a few scenarios that may help guide you in the decisions you should consider.

A home user may start with an idea that they need 2TB of external storage as they have added up the photo sizes they have on their various computers and smartphones. On top of this basic 2TB 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 for room to grow with bigger file sizes. If they want to protect their valuable memories a twin drive RAID-capable DAS or NAS may be best, so 2x 4TB is now 8TB. It will be far better value in terms of time transferring files and money spent to get the right solution first time, than realising your chosen device isn’t big enough very quickly.

A business organisation will also face the same issues, but as most rackmount storage arrays can be partially populated at purchase, expansion can be handled at demand grows. What is worth considering the type of drives you use - you could start with a 12-bay NAS and populate 4x 12TB drives, giving you 48TB space. If you configure RAID 5 you will lose one drive capacity resulting in 36TB useable 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 useable space as you only lose 6TB for parity. It is also worth pointing out that is 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 inbuilt 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 does become a consideration when using one or several data management features. As we’ve mentioned RAID reduces usable capacity, whereas compression and deduplication will act to increase useable space. If you are operating tiered storage, then you may compress and deduplicate at the cold layer, only deduplicate at the warm layer, and leave the hot layer untouched for fastest access. When looking at initial capacity required or adding extra drives, the type of drive and its intended layer location will impact your calculations.

As you can imagine every capacity decision will be different, but our friendly advisors are on hand to help if you if required - simply call 01204 474747 or email [email protected]


Choose your External Storage Solution

We hope you’re found this guide to external storage useful in informing your choice of device type, its drive types, features and connectivity - below is a quick summary table comparing the different options. Attributes are rated 0 to 5, where 0 has limited appeal or functionality and 5 represents the most suitability or a comprehensive feature set:

DAS NAS JBOD SDS Optimised Tape
Home Use 5 5 0 0 0 0
Business use 1 5 3 5 5 5
Performance 2 4 3 5 5 3
Scalability 2 4 4 5 3 5
RAID or EC Protection 0 4 0 5 5 0
Data Management Software 0 4 0 5 3 0
Data Management Software 1 3 3 5 2 2
Cost £-££ £-££££ ££-£££ £££-£££££ ££-£££ ££-£££

You can now shop our range of DASs, NAS and JBOD pre-configured or customisable solutions or alternatively learn more about our high-end SDS and optimised offerings, by clicking the links below.

Direct Attached Storage
(DAS) - Portable


Direct Attached Storage
(DAS) - Single Drive


Direct Attached Storage
(DAS) - Multiple Drive


Network Attached
Storage (NAS)


Custom JBOD and
NAS Solutions


Software Defined
Storage (SDS)


AI Optimised