How to choose the perfect M.2 SSD for you
Only fools rush into spending hundreds of pounds on storage. We set out 10 questions you must ask yourself before you spend a single cent.
1 Do I want an internal or external drive?
We’ve reviewed internal drives here, although with an external adapter you can use a USB drive instead. While USB 3.2 Gen 2 speeds are considerably faster than previous generations, they’re not as quick as internal drives by a long shot. USB 3.2 Gen 2 2x1 runs at up to 10Gbits/ sec, which works out at around 1,250MB/sec, a fraction of the maximum speeds of the latest SSDs. So why bother?
External drives are useful if you need to move data from one computer to another, or you want to take a secure backup of files, storing the drive in a different location or even a safe. External drives are also useful for devices that are hard to upgrade, such as laptops.
There’s a big disadvantage: files on an external drive aren’t accessible if the drive’s not connected. That makes external drives largely unsuitable for storing apps or files you often need.
2 Should I get an SSD or a mechanical drive?
It’s staggering to see mechanical hard disks still available. Their main advantage is that they’re cheaper than their SSD equivalent, particularly in larger sizes. So, does overall size trump the speed and quality advantages of SSDs? In most cases, no.
Mechanical disks can be helpful if you have an older device that needs one, such as a NAS drive. If, for example, you’re running an existing NAS and one hard disk fails, you’ll need to replace it with the same. Otherwise, you should buy solidstate storage instead, be that an M.2 drive or even an older SATA drive.
3 What about SATA drives?
Talking about Serial ATA (SATA), are those drives still worth buying? The simple answer is no. SATA was designed in the time of mechanical hard disks, and tops out at speeds of around 600MB/sec – that’s pretty slow in terms of today’s storage.
The first SSDs used the SATA interface in a 2.5in format, because they had to utilise an existing storage connector. Today, M.2 drives are, for the most part, designed to be used with PCI Express, so there’s very little point in buying an older SATA-based drive, mechanical or solid state.
The only exception is if you’ve maxed out your M.2 slots and need to add additional storage, with only 2.5in drive bays free in your PC. A SATA SSD is then a better choice than a mechanical hard disk.
4 Are all M.2 drives the same?
Not quite. M.2 is the name of the slot, not the interface. M.2 slots can take SATA drives, running just as slowly as they would when connected via a SATA cable, but they can also run NVMe (Non-Volatile Memory express) drives. NVMe is a communications protocol designed for solid-state storage, built to deliver the fastest speeds.
NVMe uses PCI Express, of which the two current generations are PCI-E Gen3 and PCI-E Gen4 (also written PCI-E 4.0 and PCIe 4.0). The main difference between the two is in the speeds they provide. PCI Gen3 runs at 1,000MB/sec per lane, while PCI-E Gen4 doubles that to 2,000MB/ sec. With most storage slots offering up to four lanes, that means that PCI-E Gen3 runs at up to 4,000MB/sec and PCI-E Gen4 up to 8,000MB/sec.
Support for PCI-E 4.0 depends on your processor and motherboard. At the minimum, you need a processor that supports PCI-E 4.0. It’s then essential to have a motherboard that supports the technology.
You may find support is mixed, even on the same motherboard. For example, with a Ryzen 5 5000 series processor and B550 motherboard, one M.2 slot is controlled by the CPU and runs at up to PCI-E Gen4 speeds; the other slot is controlled by the chipset and runs at up to PCI-E Gen3 speeds.
Before you buy, check what slots you have and the speeds they run at, and what speeds your CPU supports. Unless you’re planning an upgrade soon and will keep the storage, it’s not worth paying extra for a PCI-E Gen4 SSD if it goes in a PCI-E Gen3 slot. While this will work, you’ll be massively limiting the drive’s speed.
5 Can I mix M.2 drives and SATA drives?
You can, although again, you’ll need to do some research. In most cases, an M.2 slot will share a SATA connection with one port on the motherboard; the manual will tell you which. You can’t have a SATA M.2 SSD and run a SATA drive from the shared port.
In most cases, you should avoid SATA, as explained above. But, if you are going to use SATA drives, in either regular or M.2 formats, just check the motherboard’s manual first.
The restrictions don’t apply if you’re mixing NVMe and SATA drives, as there’s no overlap or sharing.
6 How much space do I need?
This is the eternal question and one that’s not easy to answer. For many people, a 1TB drive will provide more than enough storage for files and
applications, with larger backups and older files harvested off to the cloud, a NAS or external hard drive. If you play lots of games or edit many videos or photos, you may need 2TB of storage.
It’s best to err on the side of caution when estimating how much storage you’ll need. Data requirements keep growing, and there’s nothing worse than buying a new drive and seeing an “out of storage” error message.
When estimating storage, look at how many storage slots you have on your motherboard, as you can always expand storage in the future. Splitting storage between a fast application drive and a secondary storage drive for files and games can be a good way to manage your storage needs.
In short, the best answer is to buy the biggest drive you can comfortably afford. That way, you’ll give yourself the most amount of breathing room.
7 What speed drive should I buy?
Again, this is a tricky question. If you look at the marketing bumph SSD manufacturers put out, they always quote the fastest speeds their drives are capable of, but they’re not always in line with what you’ll expect, as you can see from our performance graphs. It’s actually rarely worth buying the latest and fastest drives, as you’ll pay a premium and won’t necessarily reap the rewards.
If you want a drive that’s fast at loading Windows and apps, you need one that’s fast with both sequential and random access files. If you’ve got a data storage drive for office files and photos, then neither factor is particularly important, and you probably won’t see much day-to-day difference. In these cases, it may be better to forgo the latest technology and buy a larger drive overall.
8 Do I need to worry about drive longevity?
One of the scare factors about buying an SSD is that the memory chips inside them have a finite lifespan. Each time data is written, each cell becomes less reliable until it finally fails. Eventually the drive will fail, and it’s game over.
Manufacturers estimate life using a write endurance figure. This figure is the total amount of data that can be written to the drive before it fails. It’s measured in terabytes written (TBW). For most 1TB drives it’s about 600TBW, scaling up and down with capacity.
Once the TBW figure has been exceeded, your warranty is null and void, no matter when you bought the drive. A tool such as CrystalDiskInfo will tell you the current write figure, so you can keep a check on the drive, but many drives have software available from the manufacturer that tells you the same figure.
It’s important not to get too hung up about reliability. After all, it’s not as though mechanical disks didn’t fail all the time! In most cases, SSDs will last for far longer than they’re useful: by the time a drive has failed, you’ll likely have upgraded it.
Nonetheless, you should take precautions and back up all your data. Once a drive has failed, reclaiming data is very difficult.
9 Should I use an SSD for a page file?
Run Windows 10 or 11 and you’ll have a page file. Data is moved from RAM to the page file when physical memory is full. This ensures that Windows runs smoothly and doesn’t crash, so you shouldn’t disable the feature.
One common concern about the page file is that it can needlessly cause the SSD to write data and fail. However, that’s not necessarily true. Windows 10 and 11 support the TRIM command, which simply marks blocks of data on an SSD as deleted, as opposed to erasing them. This means fewer write operations are required, which increases SSD life.
What’s more, data is evenly spread across an SSD, rather than focusing on a set of memory locations. In short, Windows will work properly with an SSD and won’t wear it out before its time. That said, it’s worth speccing your PC to have the right amount of memory for you, as this will reduce the need for paging files and increase performance.
10 Cache or no cache?
SSD manufacturers have increased capacity by increasing the number of bits stored per memory cell. Triple-Level Cell (TLC) SSDs store three bits per memory cell, while Quad-Level Cell (QLC) drives store four bits. This is great in terms of capacity, but an increase in the number of bits increases the complexity of writing data.
That’s why most SSDs have some form of cache. SDRAM cache has been used in the main, with fast memory sitting as a buffer between writes and the actual memory cells. This adds complexity and price to SSDs.
With capacities increasing, more and more SSDs are moving to Single-Level Cell (SLC) caching. This uses a portion of the SSD in Single-Level (SL) mode, writing one bit per cell. Once done, the SSD, in the background, moves the data to SLC or QLC cells. This technology can increase cache sizes and reduce the overall SSD price, but it relies on some empty SSD space. As the SSD is filled up, there’s no room for the cache, and performance deteriorates.
SLC caching drives also use Host Memory Buffer (HMB) technology, which uses system RAM for buffering and is supported by Windows 10 and 11. Ultimately, SLC caching can deliver the same or better performance than SDRAM, but buy a slightly larger drive than you think you may need.