How to choose an SSD

Which SSD to buy? Normally, we'll just tell you to follow our guide to the best storage. But during flash sales, such as on Black Friday or during the holidays, recommendations based on normal prices become somewhat irrelevant since the best deals often go to lesser-known readers (models, capacities, etc.), who may worth buying at a healthy price. reduction.

In this scenario, you may face several questions such as… Is QLC as good as TLC? Do SSDs Really Need DRAM? Why do SSDs have different shapes? Does SSD capacity affect its performance? This short guide will walk you through the fundamental differences between all types of consumer SSDs. So when you see an SSD on sale, you'll know if it's a good buy for you.

NVMe vs. SATA SSDs

The interface of the SSD not only determines transfer speeds, but also whether you will be able to install it in your system. For years, SSDs used the same SATA interface as HDDs and were either similar in shape/shape to the 2.5″ drives used in laptops; or they used the more compact mSATA form factor, which was similar to the Mini PCIe used by devices such as network cards.

With SATA 3.0 becoming a limitation on transfer speeds at around 560MB/s, the NVMe interface effectively replaces it, connecting directly to the CPU or through the motherboard chipset with multiple PCIe lanes, for much faster speeds.

Many motherboards have more connectors than they can use at once, so regardless of your choice of SATA or PCIe, you should check whether using a connector in this mode would disable another one you you need.

The Crucial MX500 is about as good as a SATA drive can get. If you want an NVMe drive, the Western Digital Black SN_750 currently offers excellent value for money.

Expansion card vs M.2 SSD

Most current SSDs, both SATA and NVMe, use the M.2 form factor, which supports up to four PCIe lanes for an NVMe SSD.

With M.2, PCIe 3.0 SSDs allow transfer speeds of up to 3500MB/s, while PCIe 4.0 SSDs benefit from speeds of up to 7000MB/s, as long as your CPU and card mother support the faster 4th generation interface.

Most M.2 SSDs are keyed to the M key, which supports up to four PCIe and SATA lanes. Some older motherboards have M.2 slots that support key B and only two PCIe lanes besides SATA.

Most SSDs that use SATA or two PCIe lanes are double-notched according to both keys for compatibility, however…

All M.2 SSDs are 22mm wide. The most common are 80mm long and are called "2280". Laptops, and mainly ultrabooks, sometimes only have room for 42mm long SSDs, called "2242". Tablets such as the Surface Pro 8 use 30mm long SSDs ("2230" ). 60mm long ("2260") SSDs are widely supported, but not common. The few that are 110mm long (“22110″) are not supported by consumer devices.

As an alternative to M.2, some PCIe SSDs come in the form of expansion cards, resembling small graphics cards and installed similarly. The larger form factor can make up for a motherboard's lack of PCIe 4.0 support by using eight PCIe 3.0 lanes, or accommodate a more powerful controller that requires better cooling. Another alternative is a U.2 2.5” SSD which can be connected to an M.2 slot with an adapter cable.

Western Digital's AN1500 is probably the fastest SSD when connected to a motherboard or PCIe 3.0 CPU only. If your system supports PCIe 4.0, then Samsung's 980 Pro is a top choice.

QLC vs. TLC SSDs

In modern SSDs, flash chip cells are made up of tiers, with each tier storing one bit (0 or 1) of data. Most SSDs today use tri-level cells (TLC) or quad-level cells (QLC). The term "multi-level cells" (MLC) was originally used to describe two-level cells, but the term "3-level MLC" used by Samsung simply means TLC.

Adding tiers to cells allows them to store exponentially more data in the same physical space, but also makes them exponentially slower to write. The good news is that you won't notice it immediately thanks to the clever caching mechanisms.

Most SSDs use some of their free storage space as a single-level virtual cell (SLC) cache by writing only to the first level of cells. Once the cache is exhausted, the drive degrades to its "native" write speed. In the case of QLC, this speed can be similar to that of a hard drive.

Whether it has QLC or TLC, the less free space your SSD has, the smaller its SLC cache will be and the shorter the time it can maintain its maximum write speed.

If you really need an 8TB SSD, the Sabrent Rocket Q is the best choice for you. If you can get by with 4TB or less, the company's Rocket 4 Plus will perform more consistently thanks to its TLC flash.

SSD without DRAM or SSD with DRAM

In order to map where each file's data is physically stored in the flash chips, most SSDs rely on their own local RAM - typically 1MB of RAM for every GB of storage space - but that's not always the case.

NVMe SSDs often use the Host Memory Buffer (HMB) to use part of the system RAM for the task. In shorter M.2 SSDs, this can be done in order to save physical space. In larger SSDs, the goal is to reduce costs.

When a drive that uses HMB is nearly empty, the lack of onboard DRAM will not noticeably affect its performance. However, if you store hundreds of GB of data on it, the speed at which it finds files can become several times slower (but still much faster than a hard drive).

With SATA SSDs, things are more complex. Instead of main system RAM, DRAM-less SATA SSDs use their own flash chips, which are much slower than any type of RAM. Additionally, storing the ever-changing index of all your data on flash chips can cause them to wear out faster and adversely affect the life of the device. For this reason, we can only recommend a DRAM-less SATA SSD as a temporary solution.

If you're looking for a short NVMe drive, then Sabrent's DRAM-less Rocket Nano is your best bet. Instead of buying a non-DRAM SATA drive, you should look for something like the Western Digital Blue SSD (2018), which is never far from the best, and often cheaper, SATA drives on sale.

250 GB vs 500 GB SSD

Over the past year, demand for low-cost PCs for working from home has made 250GB SSDs almost as expensive as their 500GB versions. On a flash sale, however, a 250GB SSD may suddenly cost the same price per GB as a similar drive with double the capacity. The question is, will the 250GB drive be good value for money in this situation?

This may not be the case for two reasons: 1) even though they use the same percentage of their free space as SLC cache as larger capacity drives, smaller drives still have smaller SLC caches to begin with. 2) Because they use fewer flash chips, they may not take full advantage of a controller designed to write to multiple chips simultaneously.

In NVMe drives, you might notice this immediately: for example, the 250GB version of the Samsung 980 (non-Pro) is rated for a maximum write speed of 1300MB/s, while the 500GB version is designed for twice that speed.

In SATA drives, you might only see the difference once the SLC cache is full. The Crucial MX500 250GB and 500GB versions both start long writes at around 450MB/s, but when their SLC caches are full, the 250GB version drops to 200MB/s, while the 500GB version stays at a respectable 400 MB/s.

If you want a good 500GB SSD at an affordable price, consider the Samsung 980 (non-Pro). Instead of buying the 250GB version, you should look to the 500GB version of Western Digital's Blue SN550 for a similar price.