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.
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.
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.
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.
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 |
 Thunderbolt |
 Wireless |
|---|---|---|
| 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 |
 InfiniBand |
|---|---|
| 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.
