The available M.2 SSD form factors have been pretty constant over the past years. Basically everything uses the M.2 2280 format, which makes the drives 22 mm wide and 80 mm long. No doubt, these dimensions are great for desktops and most laptops. With the release of the Steam Deck and ROG Ally portable game consoles, this status quo has changed. An 80 mm SSD is suddenly pretty big, considering the whole Steam Deck is just 30 cm long and 12 cm wide. That's why these new consoles use drives built on the smaller M.2 2230 form factor—just 3 cm long.

When buying a Steam Deck from Valve you can choose between a 256 GB SSD ($400) and a 512 GB model ($450). Just this week, the company announced their new OLED Steam Decks, which come at a price of $550 for the 512 GB OLED model, and $650 for the 1 TB version. There's also a 64 GB eMMC option for $350, which can be upgraded with an NVMe drive (all hardware versions have an M.2 slot). It looks like with the release of the OLED design, there will be no more eMMC version. Still, it could be a cost-effective approach to get a Steam Deck without spending too much, but you'll need to find a decent M.2 2230 SSD to achieve better storage speeds. With 1 TB being the maximum official capacity of the Steam Deck, upgrading to a 2 TB SSD could be a good way to expand your library, too. Also, a faster SSD could lead to faster installations or shorter game load times.

In the past we've reviewed two M.2 2230 drives, the Team Group MP44S and the Addlink S91, which are both based on the Phison E21 controller paired with 176-layer 3D QLC NAND from Micron. The WD Black SN770M in this review uses only in-house components. The controller is the SanDisk 20-82-10081, which is the exact same model used on the larger SN770 (without M). In terms of NAND flash we're getting BiCS5 TLC (not QLC), which is a huge selling point compared to most other M.2 2230 drives available. Just like other M.2 2230 drives, the SN770M does not include a physical DRAM cache chip, but it has support for the Host-Memory-Buffer feature, which allocates a small portion of the system's RAM for the mapping tables of the SSD. On the 2 TB variant, 64 MB are used.

Synthetic performance results of the WD Black SN770M are not impressive and well below the Phison QLC alternatives. The reason seems to be that Phison is very good at optimizing their controllers for synthetic reviewer workloads that are run on an empty drive. Only Sequential Writes are little bit better on the SN770M than on the Phison E21 drives. That's why it's important to also include real-life testing. We're even running those tests with the drives filled to 80% capacity, not empty. This approach puts additional pressure on the various algorithms and the SLC cache, just like in real-life.

The real-life performance of the SN770M is outstanding. When I first heard of the SN770 "M" I thought to myself "so they will use the same name, to profit from the good reputation of the SN770, while running at much lower performance." I was wrong—the SN770M offers virtually the same speeds as the SN770. There's some small differences due to 1 TB vs 2 TB and a newer firmware version, but overall its pretty much a tie. This also means that the SN770M is considerably faster than the Phison E21 QLC drives—by around 25% on average, which is a lot, and the opposite of what the synthetic benchmarks show. During my first M.2 2230 reviews I said that to achieve the small form factor, performance compromises have to be made, not so with the SN770M. It's one of the fastest SSDs we ever tested—no matter the form factor!

Just like all other modern SSDs, the WD Black SN770M comes with a pseudo-SLC cache that absorbs incoming writes at high speed, but uses three times the storage to do so. Our testing reveals that the SLC cache is sized at 638 GB, which means the drive will fill almost all of its capacity in SLC mode first. This is good, because a large cache allows the drive to soak up bursts of incoming write activity, for example when installing a new game. Once the SLC cache is exhausted, write speeds falls off a cliff, down to only 400 MB/s. While that is only 1/10th of the full write rate, it is still much higher than the 100 MB/s that we've seen on the QLC M.2 2230 drives. While 100 MB/s might be workable on the portable consoles, because they are limited in terms of network speed and CPU performance, 400 MB/s is much better. Filling the whole 2 TB capacity completed at 440 MB/s, which is the highest of all the M.2 2230 drives tested so far, but still much lower than what we've seen on M.2 2280 high-end SSDs.

Due to the small form factor, and lack of a heatsink, the drive will thermally throttle rather quickly when fully loaded. In my testing that happened after 17 seconds, which is still an impressive 80 GB written (i.e. almost a complete game). Here, too, you have to consider that there's no way that the console has data available at a rate of 4 GB/s, rather you'll be limited to around 150 MB/s Wi-Fi 6E speed, or even slower. Even when thermally throttled, you're still getting write speeds higher than that, and our testing confirms that there's no thermal throttling during reads, even in worst case, so your actual gaming won't be affected.

Energy efficiency is very important for a portable device, because battery life depends on it. Idle power consumption is a little better than the Phison QLC drives, but only by a small amount. While under load, the SN770M handles reads a bit more efficiently than the competition, but writes on the other hand, consume more power. Considering the Steam Deck's usage profile, which is definitely read-heavy, I think that gives the SN770M a small edge over the Phison E21.

The WD Black SN770M 2 TB is currently listed online for $220, which is a pretty steep price. A comparable desktop SSD can be found for less than $100. The WD Black SN770 2 TB sells for $110 and uses the same components. As usual, compact-sized equipment often comes with a higher price tag. The Phison-based QLC alternatives are considerably cheaper (Addlink S91 2 TB $170, Team Group MP44S $180), but also offer lower performance. If your priority is achieving the best performance for your Steam Deck, the SN770M is the best choice, albeit at a 20% higher cost compared to alternatives. However, considering the platform's modest storage speed requirements, opting for the QLC competitors is a feasible strategy to save some money.