Jesper Berg 
At some point, PC building is bound to leave you with a spare M.2 NVMe SSD that you couldn’t find a new home for. The sensible solution to this problem is to put it in an external USB enclosure and reuse it for backups, network storage, another Steam library folder, or whatever else you can think of.
But what sort of enclosure? There are plenty of options for M.2 form-factor drives and they promise to do more or less the same thing.
To help you choose, I have extensively tested a range of popular enclosures to determine if and how they differ. Keep reading to find out more.
Best M.2 Enclosures Based on Value & Functionality
Almost regardless of the SSD used, any USB 3.2 Gen 2 M.2 enclosure should be able to use all of its 10 Gbps bandwidth. The exception would be if you use a SATA SSD in the M.2 form factor, which would then of course be limited by its internal 6 Gbps interface. Although some enclosures support these drives, the drives themselves are rare and most will use at least a PCI-Express 3.0 (Gen3) SSD.
Since just about any budget NVMe drive can move data at faster rates than 10 Gbps, this also raises the question of whether you have a faster USB 3.2 Gen 2×2 (or USB4/Thunderbolt) port that comes closer to maxing out the SSD’s capabilities. There are indeed such enclosures on the market, but they are also pricier and may not offer substantial benefits (more on this later).
At this time, I would argue that 10 Gbps NVMe M.2 enclosures offer the best value for a majority of use cases. This is also the maximum usable bandwidth with a USB Type-A connector, which simplifies moving data between devices.
Last update on 2024-07-27 / Affiliate links / Images from Amazon Product Advertising API
Best Cheap M.2 Enclosure: SSK SHE-C325 Pro
Among the most affordable NVMe USB enclosures I’ve tested, the SHE-C325 Pro from SSK stands out as a decent blend of functionality, style, and reasonable price. It matches the performance of any other USB 3.2 Gen 2 model, and it also comes with a thermal pad and rigid aluminum housing.
Last but not least, the box also contains dual USB cables (C-to-A and C-to-C), which adds convenience to this USB NVMe enclosure. Since it maxes out at 10 Gbps, it can also utilize the full bandwidth with a Type-A connection.
Some compromises are nevertheless noticeable compared to slightly pricier models. All parts of the SSK enclosure, including the aluminum casing itself, are a bit more delicate compared to more expensive alternatives. It also uses a rather unconventional mechanism to lock the SSD in place, using a flexing PCB and plastic hooks. This might become an issue if you swap SSDs around a lot, e.g. for cloning.
Shopping links: Amazon, Newegg
Best Value: Ugreen SATA/NVMe Enclosure
The Ugreen SATA/NVMe M.2 enclosure has adopted a very practical and robust design. It ships with a thick thermal pad as well as a protective rubber frame. Two cables with Type-A and Type-C connectors are also included in the box. Instead of a tool-free design (which often introduces more problems than it solves), the enclosure’s finned aluminum lid has a single screw, making it exceptionally easy to swap SSDs.
Like the SSK model, Ugreen’s case uses the Realtek RTL9210B USB bridge, which supports both PCIe/NVMe and M.2 SATA SSDs. Of course, only a PCIe/NVMe drive will allow it to reach its maximum 10 Gbps sequential performance. While it offers no surprises on the performance side, what makes the Ugreen enclosure particularly attractive is an impeccable quality impression and easy operation. The only real downside to the abundance of aluminum used is that it’s also heavier than average.
Shopping links: Amazon, Newegg
Best Premium (RGB) Enclosure: Asus Strix Arion
The RGB-equipped ROG Strix Arion is a premium PCIe enclosure that comes ready to shift colors along with your gaming rig using Asus’ Aura Sync software. Instead of a Realtek USB bridge, the Asus variant uses an ASMedia ASM2362 chip that uses an internal PCI Express Gen3 x2 interface and does not support M.2 SATA SSDs. This is unlikely to be an issue for most users, as M.2 SATA drives are very rare these days.
Asus highlights that the Strix Arion enclosure features ‘screwdriver-free’ installation, but has instead opted for a tool along the lines of a SIM tray ejector pin. The SSD is then secured using a thumbscrew (and/or a flathead screwdriver). The mechanism works well enough and thick thermal pads are pre-mounted on the enclosure’s lid for a tight fit. As a result, the Arion runs quite cool despite being thinner than most competitors.
As previously noted, the performance of an M.2 PCIe/NVMe enclosure like the Asus is primarily constrained by the USB interface. In other words, the Asus enclosure is just as fast as any other 10 Gbps model, but the main selling point here is design – especially the Strix Owl RGB highlights. It’s also more robust and far less flimsy compared to cheaper enclosures like the aforementioned SSK.
Shopping links: Amazon, Newegg
M.2 SSD Enclosure Performance
As mentioned previously, the performance of an M.2 PCIe/NVMe enclosure is limited mainly by the USB interface. In general, the sequential performance of a 10 Gbps USB 3.2 Gen 2 interface will be just over 1,000 MB/s, and you can simply double that to just over 2,000 MB/s for USB 3.2 Gen 2×2.
To put these numbers in context, we have put the enclosures through some of the same tests and benchmarks that we use for testing SSDs. To eliminate any potential bottlenecks caused by the SSD, we’ve used the Samsung 990 Pro, a class-leading PCIe Gen4 drive. Needless to say, there are practically no other good reasons to put a pricey flagship drive in an external enclosure.
Sequential and Random Performance (CrystalDiskMark)
As evidenced by the CrystalDiskMark sequential performance chart, any decent M.2 enclosure will max out its interface bandwidth when connected to a sufficiently fast USB port. This also means that an external PCIe/NVMe SSD in a 10 Gbps enclosure is about twice as fast even when compared to high-end internal SATA drives.
Random performance with small chunks of data is a better proxy for overall performance in a range of everyday tasks. It also evens things out a bit compared to mainstream internal M.2 SSDs. The USB interface is still a limiting factor, as a 20 Gbps enclosure remains much slower than, for example, the internal WD Black SN770. Interestingly, write performance is still better with the entry-level (internal) SATA drive but internal M.2 SSDs are consistently ahead.
But how will an enclosure behave in a real-world-like gaming scenario? Load times in the FF XIV standalone benchmark are actually quite impressive, especially when compared to an internal hard drive. The 20 Gbps enclosure seems to offer some improvements here as well, reducing loading times by about a second. However, this benchmark combines the total loading times for five levels, so it’s a barely noticeable difference.
Is a 20 Gbps (or Faster) Enclosure Worth It?
Most M.2 SSD enclosures use a 10 Gbps USB 3.2 Gen 2 interface, which has the advantage of also being available on a relatively wide range of PCs and laptops. USB 3.2 Gen 2×2 (20 Gbps) is much less common, meaning that these enclosures will run at full speed on far fewer devices. Thunderbolt 3/4 or USB4 offers up to 40 Gbps of bandwidth but these interfaces are very rare outside of MacBooks and niche PC motherboards.
USB Bandwidth Chart
| USB 3.2 Gen 1(x1) | USB 3.2 Gen 1x2 | USB 3.2 Gen 2(x1) | USB 3.2 Gen 2x2 | Thunderbolt/ USB4 |
|
|---|---|---|---|---|---|
| Bandwidth | 5 Gbps | 10 Gbps | 10 Gbps | 20 Gbps | Up to 40Gbps |
| Formerly known as | USB 3.1 Gen 1 USB 3.0 | -- | USB 3.1 Gen 2 | -- | -- |
| Connector options | Type-A Type-C | Type-C only | Type-A Type-C | Type-C only | Type-C only |
Unlike Thunderbolt, USB is backward-compatible, so USB-based M.2 SSD enclosures can operate on slower interfaces but will be bandwidth-limited. Another limitation is that only Type-C-only cables are required at higher bandwidths than 10 Gbps.
Better Performance: Orico 20 Gbps M.2 NVMe Enclosure
If your computer is equipped with a USB 3.2 Gen 2×2 port, you may still want to max out the interface. Sequential transfer rates of more than 2,000 MB/s are better than 1,000 MB/s, after all, and will speed up your workstream if it includes moving lots of large files, such as video projects.
One option is the Orico 20 Gbps M.2 enclosure, which actually costs slightly less than the RGB-equipped Asus Strix Arion. This well-rounded aluminum enclosure is a bit heavier than its 10 Gbps counterparts, but still fairly compact. You only have to bother with a single screw and it includes a heatsink as well as a 20 Gbps-rated Type-C to Type-C cable.
Shopping links: Amazon, Newegg
Fastest NVMe SSD Enclosures: 40 Gbps USB4/Thunderbolt
The fastest external NVMe SSD enclosures on the consumer market currently achieve 40 Gbps of bandwidth over USB4 or Thunderbolt. These high-speed enclosures mainly cater to Mac users since this is the only platform where 40 Gbps USB ports are widely available. However, a small but increasing amount of high-end PC motherboards and laptops now feature USB4 connectivity.
As for enclosures that match these specifications, there are several Thunderbolt-based variants on the market such as the Acasis TBU401. This one uses an Intel JHL7440 Thunderbolt 3 controller and offers sequential performance of around 2,700 MB/s when equipped with a high-end NVMe SSD.
Shopping links: Amazon, Newegg
Compatibility: Interface, M.2 Keying & Sizes
USB interface speeds are one thing, but you also want to ensure that your spare SSD is actually compatible with the enclosure. M.2 is not an interface but a form factor that may use the SATA or PCI-Express interfaces. Additionally, M.2 SSDs come in different sizes (lengths) and with different arrangements of pins (keying).
In most cases, this is easier than it looks. Most M.2 SSDs from recent years are of the M-key variety and are 80 mm in length (22*80*). Most enclosures will also accommodate any length except the extremely rare 22110 (110 mm) size. Again, most are 2280 except for special cases like the Steam Deck.
Many enclosures, including the above-mentioned Ugreen and SSK models, also support M.2 SATA SSDs using the B+M-key pin layout, but most will be PCIe/NVMe and M-key.
Almost any PCIe 3.0 (Gen3) or newer M.2 SSD should be able to saturate 10 Gbps or even 20 Gbps worth of USB bandwidth. For this reason, it makes a lot of sense to use an entry-level or midrange SSD for an external enclosure. Using a high-end drive means that much of its performance is left on the table.
This changes once you move up to 40 Gbps over USB4 or Thunderbolt. When buying this type of high-end enclosure, it’s worth checking the fine print (i.e. compatibility charts) and selecting the right SSD to make sure that it meets your expectations.
FAQ
How do I determine my USB port versions?
The easiest way to tell on a PC is by looking for the USB SuperSpeed logo next to the port. There should be a number next to it that denotes the bandwidth, e.g. 5, 10, or 20, which corresponds to the bandwidth in Gbps.
What are the different types of M.2 enclosures?
M.2 is not an interface but a form factor, and M.2 enclosures may support SSDs built for the SATA or PCI-Express interfaces. The SSD will in turn connect to the computer via a USB bridge or Thunderbolt controller chip in the enclosure. This is what determines what SSDs are compatible as well as the enclosure's maximum theoretical performance.
Some USB bridge chips like the Realtek RTL9210B support M.2 drives using either the SATA or PCI-Express interface, whereas others only support PCI-Express SSDs (utilizing the NVMe protocol). PCIe/NVMe M.2 SSDs are typically much faster than their less common SATA counterparts.
Is a DIY enclosure/SSD combo better than an external SSD?
Not necessarily, but it gives you more flexibility with capacity and performance configurations. External SSDs often use the same USB bridge chips/Thunderbolt controllers as those found in M.2 enclosures.
What is the best SSD to use in an enclosure?
Unless it's a high-end Thunderbolt or USB4 enclosure, the best SSD pairing is with an affordable mainstream drive. This is because just about any recent PCIe Gen3 or Gen4 M.2 SSD can saturate the bandwidth of a 10 Gbps or even a 20 Gbps USB port.
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