November 16, 2022
  • November 16, 2022

WD Black SN850X SSD review: Back in black

By on August 25, 2022 0

Western Digital touts the WD Black SN850X as a high-end PCIe 4.0 SSD for gaming that has options for RGB lighting and a heatsink, making it ready for the PlayStation 5 (PS5) or your PC. The 4TB model is particularly appealing because many drives, like the SK hynix Platinum P41, are still limited to a 2TB peak. The SN850X also offers faster sequential performance and IOPS than its predecessor, the popular WD SN850, and a new 2.0 game mode to enhance your gaming experience.

It feels like the SN850X is a bit behind the times, as it’s been eighteen months since WD launched the SN850. Since then, high-end SSD gaming has evolved rapidly to include an array of serious competitors. Fortunately, the SN850X can compete with any of them, although the introductory price might be a little too steep given recent pricing trends.

We also need to test to see if WD’s new game mode is just a gimmick. We took an in-depth look at Microsoft’s DirectStorage feature in our recent Phison I/O+ firmware preview. This new feature from Microsoft will dramatically reduce game load times, and the previous-generation SN850 performed quite well in our tests, all things considered, setting the bar high for its predecessor.

WD’s NAND technology still lags its competitors, with its 112-layer BiCS5 flash competing with 176-layer flash from Micron and SK hynix. However, this has advantages, as WD’s mature flash can be carefully and reliably bundled together. BiCS5 also offers 1TB arrays for larger capacity SSDs.

The previous generation SN850 didn’t set any performance records, but we can also see improvements in the SN850X’s SSD controller across the performance spectrum. It would still be hard to beat the SK hynix Platinum P41 which tops our list of best SSDs, but WD has already surprised us. Here’s how the WD Black SN850X compares.


Product 1TB 2TB 4TB
Pricing | with HS $159.99 / $179.99 $289.99 / $309.99 $699.99
Capacity (User / Raw) 1000 GB / 1024 GB 2000 GB / 2048 GB 4000 GB / 4096 GB
Form factor M.2 2280 M.2 2280 M.2 2280
Interface / Protocol PCIe 4.0 x4 PCIe 4.0 x4 PCIe 4.0 x4
Controller Property of WD Property of WD Property of WD
Flash memory CCM BiCS5 112 layers CCM BiCS5 112 layers CCM BiCS5 112 layers
Sequential reading 7300Mbps 7300Mbps 7300Mbps
Sequential write 6300Mbps 6600Mbps 6600Mbps
Shuffle Playback 800K 1,200,000 1,200,000
Random write 1,100,000 1,100,000 1,100,000
Security N / A N / A N / A
Stamina (TBW) 600 TB 1200 TB 2400 TB
Part number | with HS WDS100T2X0E / WDS100T2XHE WDS200T2X0E / WDS200T2XHE WDS400T2X0E
Height | with HS 2.38mm/8.80±0.22mm 2.38mm/8.80±0.22mm 2.38mm/8.80±0.22mm
guarantee 5 years 5 years 5 years

The Western Digital Black SN850X is available in 1TB, 2TB and 4TB capacities. This is a change from the older SN850, which did not have a 4TB model but did have a variant of 500 GB. Also, the SN850X has options for a heatsink with RGB for the 1TB and 2TB models, but not for the 4TB drive. In contrast, the SN850 had a non-RGB heatsink option for each capacity .

WD touts the 1TB and 2TB capacities as the best for the PS5; the RGB and heatsink only add $20 to the price. The SN850X’s endurance rating remains the same at 600TB of writes per TB of capacity over five years – that’s pretty typical and more than enough for normal use.

WD improved performance in sequential read workloads, with a maximum of 7.3 GB/s from 7.0 GB/s, and sequential writes increased from 5.3 GB/s to 6, 6 GB/s. Performance in random workloads also improved significantly, going from a maximum of 1M/720,000 reads and writes, respectively, to 1.2M/1.1M.

The SN850X is competitive with other high-end PCIe 4.0 drives in sequential workloads, but it can’t quite match the SK hynix Platinum P41 in random IOPS. The price is a little steep, especially at 4TB. The SN850X will have to impress to justify its MSRP.

Game mode 2.0, software and accessories

The Black SN850X works with WD’s dashboard management software that the company includes with its SSDs. This application can quickly display drive information, including health status, while providing tools and settings.

Of particular note is the Game Mode 2.0 feature which is new with the SN850X. The original game mode can be turned on or off in the dashboard, but game mode 2.0 has an additional automatic setting to detect game launches. You can also manually enter game folder locations so the software knows where to look.

The SN850’s game mode worked by disabling low power states, ensuring the player would be more responsive. Game Mode 2.0 works differently with a three-pronged approach: predictive loading, adaptive thermal management, and overhead balancing. Predictive loading is an algorithm designed to detect upcoming low-queue-depth sequential workloads, especially read workloads prevalent in many games. Adaptive thermal management helps improve average and sustained throughput through smoother throttling. Finally, overhead balancing aims to improve read latency during gameplay through I/O prioritization.

These changes are all gaming oriented and reflect some of the things we’ve seen with Phison’s I/O+ firmware. Consistent, sustained reads are the hallmark of peak DirectStorage performance. You want to avoid peaks and dips, which can introduce jitter. Smoothing the response by avoiding throttle helps here, especially on hotter PCIe 4.0 drives. We’ve also seen Phison prioritize host I/O through scheduled background management, which WD mirrors with overhead balancing. Current games are more likely to benefit only from load times with low queue depth plays, so WD covers all its bases with predictive loading.

To look closer

We’re reviewing the base or bare-metal version of the SN850X, so our reader only has an informative label on the front. Like previous WD models, this drive is single-sided, which can benefit compatibility and cooling. The drive controller is close to the M.2 interface, one DRAM package and two flash packages.

The controller appears to be an updated version of the one found on the SN850. It’s still eight channels, but it’s paired with faster flash and improved firmware. WD tends to have great firmware, perhaps best exemplified in the SN770. The SN850 also performed relatively well in our Phison I/O+ firmware preview, with fairly consistent performance. Game Mode 2.0 optimizations should make the SN850X even better there, although it’s still too early to pass judgment on game applicability.

The DRAM module is labeled D9XPG, a 16 GB DDR4 module from Micron with a width of 16 bits. This is 2GB of memory and is the ideal ratio of DRAM to NAND for the 2TB test sample.

(Image credit: Tom’s Hardware)

WD has updated the BiCS4 found on the SN850 to BiCS5 on this drive. BiCS5 is also on SN770 and some odd drives like Sabrent’s 8TB Rocket 4 Plus. Each flash package has a capacity of 1TB, with what we expect sixteen dies per package. WD can use 512GB arrays for lower capacities, but 1TB arrays are required to keep the single-sided drive at 4TB. This indicates that the 2TB and 4TB SKUs have the ideal number of total arrays, i.e. thirty-two (four per channel), for optimum performance.

BiCS5 didn’t quite go as WD and Kioxia had originally planned. However, BiCS6 and BiCS+ still appear on target with significant changes in flash architecture. BiCS5 is apparently behind the competition, especially the 176 layer flash from SK hynix and Micron. However, WD has made the most of its flash and can handle the trade-offs by using a mature architecture.


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