Finally, the ADATA XPG Atom 50 is available in a 2 TB variant. I reviewed the Atom 50 1 TB in January and it's one of my favorite SSDs this year. It comes at affordable pricing and offers plenty of performance, thanks to a great controller and PCI-Express 4.0 support. The 2 TB version in today's review is surprisingly disappointing though. ADATA was wise to keep the 176-layer 3D TLC NAND from Micron, but instead of using the Innogrit IG5220, ADATA chose to switch to the Silicon Motion SM2269XT controller. Just like the IG5220, this is a value-oriented 4-channel PCIe 4.0 controller—actually the first Gen 4 controller from SMI that I'm testing, and I have to say I expected more.

While synthetic performance results for random read/write and sequential read/write are pretty good and in-line with the product's positioning, the 4K mixed performance is terrible. Our "Mixed" IO test randomly submits a read or write to the drive, with equal probability, which makes things much more interesting than just a continuous stream of reads, or writes. In real-life situations a drive will never execute just one type of operation—on a modern operating system like Windows or Linux there's always some background processes active, that generate various disk traffic patterns. We tested this in more detail on page 5, "Mixed Accesses", and the results are shocking. While you can get 190,000 IOPS with 100% reads, as soon as you sprinkle in just 1% of writes, performance drops by half (!!). When running a 50/50 mix of read/write, there's barely 20,000 IOPS left—a 90% loss in performance. Given this huge drop in performance, I hope this is just a bug that can be fixed with a firmware update. If ADATA provides such an update I'll retest the drive of course, and update this review accordingly.

These results show that real-life performance testing is very important, as it can help uncover such weaknesses easily. We're also testing at 80% disk full, which is a more challenging scenario than testing an empty drive, no customer will ever use an empty SSD. Here the XPG Atom 50 reaches performance similar to Gen 3 midrange drives like the HP EX900 Pro, Kingston A2000 and Samsung 970 EVO. Compared to the Atom 50 1 TB, which uses a different controller, the performance difference is a whopping 19%. This makes the Atom 50 2 TB the slowest PCIe 4.0 drive I've tested so far. When you look at specific benchmarks, such as WinRAR, or ISO File Copy, you can clearly see how the low mixed IO performance holds the drive back. In those tests a piece of data is read off the drive, processed in some way and then written back—exactly the scenario that is so weak on the Atom 50 2 TB. On the other hand, game load times are very good, among the best we've ever seen. Game load times are pure reads, so here the drive can show off its muscle.

The Atom 50 2 TB is also really good at handling huge incoming write bursts. While the SLC cache size isn't particularly big at 320 GB for a 2 TB drive, it's still reasonably sized. What makes a huge difference though is that even when the cache is full, the drive can handle incoming writes at almost 3 GB/s. Filling the whole 2 TB capacity completed at 1.95 GB/s, which is among the best results in that test that we've ever seen. If you are looking for a value-oriented drive that has to get filled with lots of data quickly, then the Atom 50 2 TB is a great choice.

Thermals were no problem either, the Atom 50 never throttled in our testing, not even in our thermal stress test—even when the included optional heatspreader wasn't installed. What I like about the SMI controller is that it reports two temperatures: one for the controller itself and one for the NAND flash chips. This makes it much easier to get a feel for the drive's health—most other drives only have one sensor, inside the controller, and it's often fairly inaccurate. Given our good temperature results, I think installing the heatspreader is optional, unless you have really bad airflow in your case.

Priced at $200, the XPG Atom 50 2 TB does not exactly stand out from the pack. While $200 is certainly at the lower end of the spectrum for a 2 TB Gen 4 SSD, the performance simply isn't there. The drive is as fast as just a Gen 3 SSD, so I see no reason why you should pay $200 for it. There's several very compelling alternatives out there, such as the WD Blue SN570 ($170, 9% faster), SN770 ($200, 14% faster), Silicon Power XS70 ($200, 13% faster, with DRAM), MSI M470 ($190, 10% faster, with DRAM). Given the current performance numbers, ADATA will have to bring the price of the Atom 50 2 TB down to around $150, or fix the low random mixed IO performance. As mentioned before, if they come up with a fix, I'll retest the drive and update this review.