HDD Buying Guide
What are HDDs?
HDDs (hard disk drives) are the most cost-effective type of data storage drive for desktop PCs, laptops and workstations. HDDs store data on spinning magnetic disks, as opposed to SSDs (solid state drives) which store data on memory cells. HDDs are usually distinguished by a colour or name branding to show what use they are intended for.
Although HDDs are a much older technology than SSDs, both types of storage drive still have a place, as their features and costs differ significantly. In this guide we’ll run you through all the details of the types of HDDs - how they work, the pros and cons of each and the scenarios where each is best suited. If you want information on solid state drives or either type of drives for servers, you can learn more by reading our SSD Buyers Guide or Datacentre Storage Drive Buyers Guide.
What HDDs should I choose?
In most cases the type of device you are using will dictate to a large degree what kind of storage drive to choose - this may be due to size and weight, cost, performance or a combination of these.
HDDs for Desktops
Most desktop PC cases have several 2.5 and 3.5in drive bays for HDDs and they are an ideal way to add significant capacity without much cost. HDDs are best used for storing infrequently used data or less performance sensitive applications. If your desktop PC is used for gaming or content creation then you should store as many of these files on an SSD for better performance. You can learn more about drives suitable for gaming and content creation in our dedicated SSD Buyers Guide.
As desktop PCs are rarely moved and in a home environment it is unlikely that the spinning nature of HDDs will cause any issues in the way of potential damage. As of April 2023, 26TB is the largest single drive size on the market, which on the face of it is an enormous amount of data. That said, it should be noted that all this data in a single place may pose issues should the drive fail, therefore it may be wise to have a secondary USB drive available to use as back-up for any critical files.
HDDs for Laptops
Although it is possible to install a small 2.5in HDD into some laptops, it is rarely recommended as the nature of a laptop lends itself to being carried around and used in a variety of locations. For this reason, it is advisable to use an SSD instead of a HDD as they have no moving parts that can be easily damaged if you knock or drop your laptop. Furthermore, SSDs are lighter and consume less power than HDDs. You can learn more about drives suitable for laptops in our dedicated SSD Buyers Guide.
HDDs for Workstations
For a workstation system or project drive, SSDs are a better choice than HDDs as they are much faster. However, HDDs provide a cost-effective way to store infrequently or bulky assets. That said, if you have multiple large HDDs - anything above 10TB - then it is advisable to use RAID protection (more on this later in the guide) to keep your data safe.
HDDs for NAS
NAS (Network Attached Storage) boxes are a little different from PCs, laptops and workstations. Firstly, the OS is inbuilt on the NAS, so you’re only looking for data storage drives. A NAS box is a good way to share files in a home or small office environment and can be very cost effective for large capacities using 3.5in HDDs - always look out for vibration resistant NAS-grade HDDs if you have greater than four drive bays in your NAS, as the lateral vibration produced by multiple spinning disks affect performance and drive lifespan. You can learn more about storage drives for NAS boxes by reading our dedicated NAS buyers guide.
HDD Sizes and Types
Now we’ve mentioned broadly the type of drive to look for depending on your device, let’s look at the difference between them in more detail. There are two main drive sizes - 3.5in and 2.5in, as you may expect the larger size allows for larger capacities. Aside from size it is the intended usage that defines the other main differences between drives.
General use HDDs are designed for typical PC use of a few hours a day, whereas NAS-grade drives are designed to work 24/7. They will likely feature a longer warranty period to reflect this and NAS Pro drives will also feature vibration resistance to counteract the effect of many drives spinning together in a NAS chassis. Similarly, NAS-grade AV or surveillance drives are additionally write-optimised due to the demands of multiple video feeds from a network CCTV system. Although general HDDs will work in any of these scenarios, you will find that drive failure rates are higher as they are not intended for such intensive use. Regardless of drive type they all have a common SATA interface, now in its third generation (SATA-III) delivering data throughput rates of up to 600MB/s.
HDD vs SSD
Although this is an HDD guide, there is no escaping the fact that HDDs and SSDs are interchangeable and complementary in many situations. So it is worth knowing the difference between them, as there are advantages and disadvantages to each, whether it be performance, cost or noise - the below table shows a feature comparison of HDDs and SSDs.
| 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 a laptop |
| Energy Use | 6-15W | 2-5W | SSDs are much more energy efficient |
| Noise | 20-40dB | Silent | No noise from SSDs |
| Capacity | Up to 26TB | Up to 15TB | HDDs provide more capacity |
| Cost | £-££ | ££ - ££££ | SSDs are more expensive, especially at high capacities |
Although SSDs clearly have the edge over HDDs in most aspects, there are still specific uses where HDDs excel, dictated by their price to performance ratio. HDDs are much more cost-effective than SSDs - a key fact in a use case such as data archiving, where capacity is more important than access speed. This lower performance but cost effectiveness is due to how HDDs work, as shown below.
How HDDs Work
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 1s and 0s that store data. The magnetisation state of the platters is physically changed by an arm that passes over the platter and writes the data to a section of it. Once data is stored on the platter by way of magnetisation it will remain in this state even when the power is off and the platters stop spinning, until it is either written over with new data or deleted altogether. 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 HDD capacity gets larger there is greater latency in retrieving data from it, as the arms physically have to trace a larger area of bytes distributed over multiple platters. For this reason, HDDs come in variety of spin speeds that have an impact on the rate at which data can be written and retrieved from the HDD - typical speeds range from 5,400rpm to 15,000rpm, but the lower 5,400rpm and 7,200rpm speeds are common in consumer or prosumer systems. It is also worth noting that as you fill up a HDD with data its performance goes down, caused by data fragmentation as files are split over several sections of the drive depending on what space was available at the time of writing. When it comes to reading the data the arms have to find the fragmented sections of it and piece it together so it makes sense. This is one factor why using many smaller capacity drives can be better than a single or fewer large ones. The below table highlights the different performances, costs and typical uses of HDD types.
| 5,400rpm | 7,200rpm | 10,000rpm | 15,000rpm | |
|---|---|---|---|---|
| Capacity | High Capacity | High Capacity | Medium Capacity | Low Capacity |
| Read / Write | Low Performance | Medium Performance | High Performance | Highest Performance |
| Typical Device | Laptop / Desktop | Laptop / Desktop / Workstation | Server / Storage | Server / Storage |
| Cost | £ | ££ | £££ | ££££ |
Data Security
When considering which HDD to buy 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 a way of spreading the data across 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 important, it is not recommended for storing critical data.
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.
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.
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 with critical data.
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.
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.
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.
Systems that support RAID arrays will usually have a hot-swap capability, meaning that a failed drive can be removed from the array without powering the system down. A new drive is put in the failed drives 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 that the rebuild can start without the failed drive being removed first.
It is also worth mentioning that multiple RAID arrays can be configured in a single system - it may be that RAID 1 is employed to protect a pair of HDDs for the OS, whereas multiple drives are protected by RAID 6 including hot spare drives too. Ultimately however, the RAID configuration(s) you choose need to be controlled, either by software on the system or additional hardware within it. Let’s take a look at the options.
Hardware RAID
In a hardware RAID setup, the drives connect to a RAID controller card inserted in a PCIe slot or integrated into the motherboard. This works the same for larger servers as well as workstations and desktop computers, and many external drive enclosures have a RAID controller built in. High-end hardware RAID controllers can be upgraded with a cache protector, these comprise a small capacitor which in the event of power loss keeps powering the cache memory on the RAID controller for as long as three years. Without a cache protector, data stored in the RAID controllers cache will be lost and could cause data corruption.
| Advantages | Disadvantages |
|---|---|
| • Better performance, especially in more complex RAID configurations. Processing is handled by the dedicated RAID processor rather than the CPUs which results in less strain on the system when writing backups, and less downtime when restoring data • Has more RAID configuration options including hybrid configurations which may not be available with certain OSes • Compatible across different OSes. This is critical if you plan to access your RAID system from say, Mac and Windows. Hardware RAID would be recognisable by any system |
• Since there’s more hardware, there’s more cost involved in the initial setup • Inconsistent performance for certain hardware RAID setups when using SSDs • Older RAID controllers disable the built-in fast caching functionality of SSDs that are needed for efficient programming and erasing onto the drive |
Chipset RAID
Many AMD and Intel motherboard chipsets support some of the basic types of RAID, potentially negating the need for a hardware RAID controller.
| Advantages | Disadvantages |
|---|---|
| • No additional cost - all you need to do is connect the drives and then configure them in the OS • Modern CPUs are so powerful they can easily handle RAID 0 & 1 with no noticeable performance hit |
• You’re restricted to the RAID levels your motherboard chipset supports • Performance hit if you’re using more complex RAID configurations • Limited performance and resilience compared to hardware RAID controller • If the motherboard dies you lose access to the RAID array |
Software RAID
The third and final type of RAID array is called software RAID and is when you use the operating system to create a RAID. Numerous operating systems support RAID, including Windows and Linux.
| Advantages | Disadvantages |
|---|---|
| • No additional cost - all you need to do is connect the drives and then configure them in the OS •Modern CPUs are so powerful they can easily handle RAID 0 & 1 with no noticeable performance hit |
• Software RAID is often specific to the OS being used, so it can’t generally be used for drive arrays that are shared between operating systems • You’re restricted to the RAID levels your specific OS can support • Performance hit if you’re using more complex RAID configurations • If the OS dies you lose access to the RAID array |
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