Corsair EX400U Portable SSD 4TB review - The external USB4 SSD is hot, fast and expensive
Hot stuff.
The Corsair EX400U is one of the first external SSDs with USB4 40 Gbps support and is said to achieve up to 4,000 MB/s in sequential reading. In the test, we look at the performance, power consumption and heat development of the drive.Klaus Hinum (translated by Klaus Hinum) Published 🇩🇪
Verdict - Fast and hot
The Corsair EX400U is an extremely fast external SSD with USB4 interface. In our benchmarks it even overachieved the advertised 4,000 MB/s (diskspd sequential read). The compatibility also looks very good and the drive worked perfectly with devices running macOS 26 (M4 Pro MBP14), iPad OS 26 (M4 iPad), ChromeOS (Lenovo Chromebook), iOS (iPhone 16 Pro for ProRes directly on the SSD), and Windows 11. The chassis is pleasantly small and with the built-in MagSafe ring on the underside, the SSD can also be practically mounted on an iPhone or even a desktop case out of metal. Using the iPhone you can also use the SSD as a hand warmer, as the heat development is the clear disadvantage. The cooling via the aluminum housing works well for the internal components, but we measured up to 69 °C under load on the top - hot stuff!
Pros
Cons
Price and availability
At currently 420 Euros from the cheapest sellers, the large 4TB version is by no means a bargain. The slower Samsung Portable SSD T9 is currently almost 100 euros cheaper (Geizhals).
The Corsair EX400U 4TB (CSSD-EX400U4TB) is powered by the Phison PS2251 controller, which offers native USB support. According to Corsair, the used TLC NAND memory chips are from Kioxia. The SSD offers a 3-year warranty as long as the TBW (Tobal Bytes Written) of 1,000 terabytes (for the 4TB model) is not exceeded. As a special feature, the SSD offers a MagSafe ring on the back. This allows the SSD to be attached to all current iPhones and, for example, to write ProRes directly to the SSD on the iPhone 16 Pro in the test.
Specifications
| Performance | up to 4,000 MB/s sequential read | up to 3,600 MB/s sequential write |
|---|---|---|
| Interface | USB4 40 Gbps | Thunderbolt 4 and 5 |
| Dimensions | 64.3 x 64 x 12 mm | 49g or 65g with USB-C cable |
| Controller | Phison PS2251 |
Performance
We measured the performance of the external storage medium on various devices. Using the Asus Zenbook OLED with the fast Intel Core Ultra 9 288V, we achieved excellent performance values that even just exceed the specifications for sequential reading (diskspd test). The Corsair performs exceptional in the synthetic read and write tests and also does not dissappoint in the other synthetic tests. In the AS SSD Copy benchmark, however, the performance clearly falls behind fast integrated SSDs.
With PC games getting bigger and bigger, the use of the SSD for the Steam library is also a good idea. In the Final Fantasy XIV Dawntrail benchmark, we compare the loading times and performance with the internal 1TB SSD of the Asus Zenbook OLED. There are no significant differences here.
* ... smaller is better
Throttling of the SSD, no noticeable problems
Performance on the iPad Pro M4
Using an iPad Pro (M4 from 2024 with 256GB base SSD) the performance of the Corsair SSD is impressive. More than twice as fast read performance and 66% faster write performance speak for themselves. However, it does not come close to the maximum 4,000 MB/s. The iPhone 16 Pro is a different story, as the USB port allows significantly less performance. The EX400U only achieves 860 / 770 MB/s (read / write). However, at least when writing, it is even slightly faster than the internal 128GB SSD.
Power consumption - could be improved without load
We measure the power consumption directly at the USB-C port with the Power-Z dongle. The Corsair SSD cannot score without load. We always measure around 1.3 watts. In comparison, an older Samsung T7 Shield, also with 4TB, only needs 0.33 watts. The Samsung X5 Thunderbolt SSD 1TB is even more power-hungry at 2.2 watts.
The EX400U is pleasantly economical under load. We only measure between 1.3 and 3.3 watts. In the AS SSD copy benchmark, the maximum is 2.2 watts. Especially in view of the high temperatures, it is questionable whether the Power-Z dongle is not displaying the correct values here. The Samsung T7 requires up to 2.8 watts under load and the X5 between 4 and 6.7 watts in comparison.
Heat development
Looking at the heat dissipation, it quickly becomes clear that Corsair uses the small metal case as a heat sink. Even without load, the case gets warm with a maximum of 41°C / 106°F on the top (35°C / 95°F on the bottom) at 23°C / 73.4°F ambient temperature. Under load, we got up to 69°C / 156 °F in the PCMark Storage load test (which ended with an error) - risk of burns!
Conclusio
The Corsair EX400U is a very fast external USB4 SSD that impresses with its high performance and compact design. A disadvantage is the high heat development under load and the currently relatively high price.
Transparency
The selection of devices to be reviewed is made by our editorial team. The test sample was freely purchased by the author at his/her own expense. The lender had no influence on this review, nor did the manufacturer receive a copy of this review before publication. There was no obligation to publish this review. As an independent media company, Notebookcheck is not subjected to the authority of manufacturers, retailers or publishers.
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