Corsair EX400U review: A compact, fast, and affordable external SSD

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The Corsair EX400U is easily the smallest USB4 SSD I’ve yet tested. It’s also good looking and a fast reader, though write performance is more like what you’d see from 20Gbps USB SSDs. Still, considering the low pricing, it’s a very desirable external storage device.

Read on to learn more, then see our roundup of the best external drives for comparison.

What are the EX400U’s features?

The EX400U is an external USB4 SSD rendered in pewter and measuring around 2.5-inches square by just shy of an inch thick. Weight is a mere, but palpable-in-the-hand 1.8 ounces — it isn’t so light it feels cheap.

The big surprise for me was that the white circle (don’t let the artistic lighting fool you) on the bottom of the unit is magnetic. It was kind of fun sticking the drive to various metal surfaces (including the ruler).

Sadly, most of the surfaces I’d like to stick it to are non-ferromagnetic, like my aluminum Mac Studio. I say sadly because it’s the perfect shape and size to hide behind said unit.

Kudos to Corsair for actually revealing what’s inside the EX400U, as I had no desire to dissect it and most vendors just clam up when asked. The controller is a Phison PS2251-21 and the NAND is layered TLC.

That controller is actually designed for USB4 and eliminates a bulky bridge chip to keep the price and weight down. Alas, it doesn’t seem to perform quite as well as the ASMedia ASM2464PD found in many pricier competitors.

Corsair warranties the EX400U for three years, or 250 TBW (terabytes that may be written before it becomes a read-only hockey puck) for every 1TB of capacity. That’s less than half the TBW rating we normally see with TLC NAND, and more in line with what QLC SSDs are rated for. (I’m kidding about the hockey puck!)

How much is the EX400U?

The Corsair EX400U is available in 1TB, 2TB, and 4TB capacities for $130, $190, and $350 respectively. That’s hardly dirt cheap, but considerably more affordable than the Adata SE920 and OWC 1M2 competition.

It even works out a bit cheaper than the Ugreen CM850 or CM642 enclosures — depending on what capacity and quality of SSD you populate those empty USB4 products with.

But those are all faster products…

How fast is the Corsair EX400U?

I kind of let the cat out of the bag on this topic up top. While the EX400U competes well with the competition in multi-queued reading, it’s writing and single-queue performance was more like that of a 20Gbps (USB 3.2×2) SSD than a full-on USB4 SSD like the Adata SE920 and OWC Express 1M2.

Note that the Ugreen CM850 (PCWorld reviewed the ever-so-slightly slower CM642) is an unpopulated enclosure that we tested with a very fast 8TB WD SN850X inside. The EX400U’s best number by far was in the eight-queue sequential read. Note that Windows only uses one queue for its I/O.

The Corsair EX400U was more competitive in CrystalDiskMark 8’s random tests, actually proving the fastest in the single-queue, single-thread write by 4MBps.

Our 48GB transfer results corroborated the CrystalDiskMark numbers. While fast, the EX400U was significantly off the pace set by the other USB4 SSDs we’ve tested.

The EX400U’s slower write rate is also reflected in the 450GB transfer, though it’s still the 7th fastest time we’ve seen from any external SSD.

While the performance discussion above may come off a bit negative, that’s only compared to other USB4 SSDs — all of which are very, very fast. The EX400U still ranked 7th place overall — faster than every 20Gbps SSD we’ve kicked the tires on as well as a number of Thunderbolt 3/4 SSDs.

Should you buy the Corsair EX400U?

I say, yeah. While it’s not the fastest 40Gbps SSD out there, it is very affordable and far more compatible across PCs and Macs than 20Gbps USB 3.2×2 SSDs. It’s also nicely light and compact.

How we test

Drive tests currently utilize Windows 11, 64-bit running on an X790 (PCIe 4.0/5.0) motherboard/i5-12400 CPU combo with two Kingston Fury 32GB DDR5 4800MHz modules (64GB of memory total). Both 20Gbps USB and Thunderbolt 4 are integrated to the back panel and Intel CPU/GPU graphics are used. The 48GB transfer tests utilize an ImDisk RAM disk taking up 58GB of the 64GB of total memory. The 450GB file is transferred from a 2TB Samsung 990 Pro which also runs the OS.

Each test is performed on a newly NTFS-formatted and TRIM’d drive so the results are optimal. Note that in normal use, as a drive fills up, performance may decrease due to less NAND for secondary caching, as well as other factors. This can be less of a factor with the current crop of SSDs with far faster late-generation NAND.