The Spatium M390 is MSI's newest entry to their growing line-up of solid-state drives. While the M480 and M470, their first products, were created to maximize the potential of the PCI-Express 4.0 interface, the M390 in today's review is a cost-optimized solution. It uses the brand-new Phison E15T controller, which seems to be the successor to the highly popular E12, but with support for DRAM-less operation. On an SSD, the DRAM cache is used to buffer the mapping tables of the SSD, which keep track of where a certain piece of data is located. Basically, it translates between linear disk addresses as seen by the operating system and the actual location of the data—which NAND flash chip at which address in that chip. Your files are not stored as a contiguous block of bytes in an SSD, either. Rather, the parallel nature of multiple flash channels is utilized to spread the data over multiple channels/NAND dies to profit from parallelization—this is what achieves multi-Gigabyte transfer rates. While the DRAM cache is one of the cornerstones of SSD performance today, it is also a cost factor. Typically, you need 1 GB of DRAM per TB of SSD capacity, which adds a few dollars to the production cost. That's why DRAM-less drives can be more affordable. The flash chips are the newest 3D TLC NAND chips from Micron, with 176-layers. We saw these in action in our Phison E18+Micron 176-layer Preview and were mighty impressed.

Synthetic random IOPS numbers of the Spatium M390 are very good. If you take a closer look, they even beat many PCI-Express 4.0 drives. It seems Phison focused A LOT on improving IOPS at low queue depth, which is the most important performance metric for today's consumer workloads. Sequential performance is good, too, roughly in the region you'd expect from a PCI-Express 3.0 SSD. Only mixed IO, both sequential and random, is noticeably weaker, possibly due to the DRAM-less design. Overall, the Phison E15T controller can impress in our synthetic testing, I'm sure it has been optimized for synthetic workloads on an empty drive, which is how most reviewers benchmark SSDs.

Good that we have our real-life test suite, too, which runs the actual applications, not a purely synthetic workload. We also test at 80% drive full capacity, which puts additional stress on the controller, SLC cache, and mapping table algorithms. Here, the MSI Spatium M390 does very well, too, achieving the second-best performance we've ever seen for a DRAM-less SSD. Only the Samsung 980 non-Pro is faster. I have to admit this is very impressive work by Phison. The M390 is faster than the Samsung 970 EVO, which is a very important win. Just as important is that the M390 can beat value drives like the WD Blue SN500-series, Sabrent Rocket Q, ADATA Falcon & Swordfish, Corsair MP400, Crucial P1, and HP EX900 Pro. PCIe 3.0 flagship drives, like the HP EX950, ADATA SX8200 Pro, Samsung 980 and SK hynix Gold P31, are 4–5 % faster, which is not a lot. The best Gen 4 SSDs, which are much more expensive, are up to 11% faster, with bigger differences in specific workloads.

Looking at my real-life results, I'd be unable to tell that this a DRAM-less SSD. There might be a hint of it in the WinRAR test, which sends a lot of random small file writes to the drive, but the differences are not big enough to make it a clear issue. I did a special round of synthetic testing to determine the performance characteristics of random writes at various test sizes, and the Phison E15 can impress here, too. Its performance for small test areas is slightly better than that of the Samsung 980—roughly twice as good as other DRAM-less drives. Once the test area is increased beyond 8 GB, the Samsung controller gains the upper hand, though.

A noteworthy issue is that the drive's write speeds will fall off a cliff as soon as its pseudo-SLC cache is exhausted. This behavior is completely unexpected, and I've never seen it before. Since this is my first review of a Phison E15T-based drive, I suspect it's the way the controller is designed to operate. A firmware bug could be possible, too, in theory, but in my experience, Phison does their homework, and such issues don't make it into production. I did reach out to Phison directly to ask for more details. I'll update this review when I hear back from them.

Otherwise, sequential write performance is good. The SLC cache is perhaps a bit on the small side. 63 GB is alright, but competing drives offer a bit more, which has them soak up bigger write bursts. As mentioned before, we're testing our real-life benchmarks at 80% disk full, so the SLC cache size is already taken into account for our real-life performance results, which are very good indeed. Of course, momentarily stopping the write activity will have the SLC cache free up capacity immediately, so full write rates are available as soon as you give the drive a moment to settle down.

Unlike some other M.2 NVMe SSDs, the MSI Spatium doesn't come with a heatsink preinstalled. In our thermal stress test, we saw only minimal throttling, so I wouldn't worry about it much, especially considering the positioning of the drive. We managed to see some throttling, but only after almost 10 minutes of hammering the drive, which basically makes it a non-issue. I'm still surprised performance completely stagnates with the drive dropping from 1000 MB/s to 50 MB/s once it reaches its thermal limit, though. While it only lasts for a few seconds, I feel a more gradual thermal throttling behavior like on other drives would have been much better. Thermal throttling starts at 78°C measured surface temperature, which is very conservative. Had MSI allowed a few degrees more, thermal throttling might have been avoided completely.

According to MSI, the Spatium M390 will retail for $110, which is a very competitive price point, especially considering the product is brand-new, just getting introduced. Looking at the design and components used, I suspect this drive has the potential to be a value king—sub-$100 seems possible. This is a huge achievement for Phison, and I'm sure it'll put pressure on the other vendors, too. At the current price point of $110, the Spatium M390 faces strong competition from drives like the ADATA SX8200, which currently sells for $110, and the Kingston A2000, also $110, with DRAM cache, but slightly lower overall performance. The Spatium M390 also has the potential to kill all the various QLC-based Gen 3 SSDs on the market because it offers considerably better performance at similar or better pricing. If you are willing to spend a few dollars more, the Samsung 980 ($120) and Hynix Gold P31 ($135) are worth checking out—they are the fastest PCI-Express 3.0 drives on the market. The latest PCIe Gen 4 drives are much more expensive and not that much faster unless the majority of your workloads is sequential.