WD Black SN850X SSD Review: Back in Black (Updated)

Update 13th October 2022: We've updated this article with new testing for the 1TB WD Black SN850X SSD on page 2.

Original Review published 25th August 2022

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 especially enticing as many drives, like the SK hynix Platinum P41, are still limited to a peak of 2TB. The SN850X also has faster sequential performance and IOPS than its predecessor, the popular WD SN850, and a new Game Mode 2.0 to improve your gaming experience. This drive is also one of the Best SSDs for the PS5. 

It does feel like the SN850X is a bit tardy, as it’s been eighteen months since WD launched the SN850. Since then, the high-end SSD game has evolved rapidly to include an array of serious contenders. Luckily, the SN850X can compete with any of them, although the launch pricing might be a bit too lofty given recent pricing trends.

We also need to test to see if WD's new Game Mode is just a gimmick. We took a deep-dive look at Microsoft's DirectStorage feature in our recent Phison I/O+ firmware preview. This new Microsoft feature will drastically reduce game loading times, and the previous-gen SN850 performed fairly well in our tests, all things considered, setting a high bar for its predecessor.

WD's NAND technology still lags behind its competitors, with its 112-Layer BiCS5 flash competing against 176-Layer flash from Micron and SK hynix. However, this has advantages, as WD's mature flash can be carefully and reliably binned. BiCS5 also has 1Tb dies available for higher-capacity SSDs.

The previous-gen SN850 didn't set any performance records, but we can also see improvements to the SN850X's SSD controller across the performance spectrum. It’d still be a hard sell for this to beat the SK hynix Platinum P41 that leads our list of Best SSDs, but WD has surprised us before. Here's how the WD Black SN850X stacks up.  

Specifications

The Western Digital Black SN850X is available in 1TB, 2TB, and 4TB capacities. This is a departure from the earlier SN850, which had no 4TB model but did have a 500GB variant. In addition, 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 every capacity. 

WD touts the 1TB and 2TB capacities as the best for the PS5; the RGB and heatsink only add $20 to the price tag. The SN850X's rated endurance remains the same at 600TB of writes-per-TB of capacity over five years — this is pretty typical, and more than enough for normal use.

WD improved performance in sequential read workloads, with a maximum of 7.3GBps from 7.0GBps, and sequential writes improved from up to 5.3GBps to 6.6GBps. Performance in random workloads has also improved significantly, up from a maximum of 1M / 720,000 read and write, 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. Pricing is a bit stiff, particularly 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 information about the drive, including health status, while also providing tools and settings.

Of particular note is the Game Mode 2.0 feature that's new with the SN850X. The original Gaming Mode could be turned on or off within the Dashboard, but Game Mode 2.0 has an additional Auto setting to detect game launches. You can also manually enter game folder locations so the software knows where to watch.

The SN850's Gaming Mode worked by disabling lower power states, ensuring the drive 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 - particularly the read workloads prevalent in many games. Adaptive thermal management works to improve average and sustained throughput via smoother throttling. Finally, overhead balancing seeks to improve read latency while gaming through I/O prioritization.

These changes are all geared towards gaming and reflect some of the elements we saw with Phison's I/O+ firmware. Consistent, sustained reads are a hallmark of optimal DirectStorage performance. You want to avoid peaks and troughs, which can introduce jitter. Smoothing out the response through throttle avoidance helps here, particularly on hotter-running PCIe 4.0 drives. We also saw Phison prioritize host I/O via scheduled background management, which WD mirrors with overhead balancing. Current games are more likely to benefit only in load times with low queue depth reads, so WD is covering all of its bases with predictive loading.

A Closer Look

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

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The controller appears to be an updated version of the one found on the SN850. It’s still eight-channel but is paired with faster flash and improved firmware. WD tends to have excellent firmware, perhaps best exemplified in the SN770. The SN850 also did relatively well in our Phison I/O+ firmware preview, performing quite consistently. The Game Mode 2.0 optimizations should make the SN850X even better there, although it’s still too early to make judgments on game applicability.

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

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

BiCS5 didn’t quite pan out the way WD and Kioxia had originally planned. However, BiCS6 and BiCS+ still appear on target with important changes to the flash’s architecture. BiCS5 is ostensibly behind the competition, particularly the 176-layer flash from SK hynix and Micron. However, WD has made the most of its flash and can manage trade-offs by using a mature architecture.

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