April 1, 2021 Update: We've updated this article with new testing for the 2TB WD Black SN850 M.2 NVMe SSD on page 2.
Original Review published December 11, 2020:
Boasting bleeding-edge PCIe Gen4 performance and available in up to 2TB of capacity, WD’s Black SN850 is a beast of an SSD that rival’s Samsung’s 980 PRO for the best SSD. If you got the cash, it is a great choice for gamers and enthusiasts looking for top-tier, quality storage.
WD’s Black product line has adapted quite a bit over the years. When it came to the company’s mechanical HDD line, Black traditionally meant uncompromising performance and reliability. Still, when it comes to the company‘s SSDs, WD’s Black product line emphasizes gaming above all. However, that doesn’t mean that the company forgot about those that need consistent prosumer storage for their applications.
The last WD Black SN750 was a data-writing powerhouse, with sustained write speed that could make nearly any other SSD jealous, making it perfect for video editors and those who often move large data sets around. But its read performance lagged most of its competition in most of our application benchmarks. The new WD Black SN850 aims to put on a much better showing this time around, with much of the company’s focus on optimizing the new SSD’s read speed as much as improving its already-strong write speed.
|Product||Black SN850 500GB||Black SN850 1TB||Black SN850 2TB|
|Capacity (User / Raw)||500GB / 512GB||1000GB / 1024GB||2000GB / 2048GB|
|Form Factor||M.2 2280||M.2 2280||M.2 2280|
|Interface / Protocol||PCIe 4.0 x4 / NVMe 1.4||PCIe 4.0 x4 / NVMe 1.4||PCIe 4.0 x4 / NVMe 1.4|
|Controller||WD_BLACK G2||WD_BLACK G2||WD_BLACK G2|
|Memory||BiCS4 96L TLC||BiCS4 96L TLC||BiCS4 96L TLC|
|Sequential Read||7,000 MBps||7,000 MBps||7,000 MBps|
|Sequential Write||4,100 MBps||5,300 MBps||5,100 MBps|
|Random Read||800,000 IOPS||1,000,000 IOPS||1,000,000 IOPS|
|Random Write||570,000 IOPS||720,000 IOPS||710,000 IOPS|
|Endurance (TBW)||300 TB||600 TB||1,200 TB|
With peak sequential performance up to 7/5.3 GBps of sequential read/write throughput and upwards of 1,000,000/720,000 random read/write IOPS, the WD Black SN850 delivers top-tier performance over the PCIe 4.0 x4 NVMe 1.4 interface. WD’s Black SN850 is available in capacities of 500GB, 1TB, and 2TB with street pricing listed at $150, $230, and $450, per respective capacity. If you want the model with a heatsink, it will cost an extra $20.
WD’s Black SN850 features a revamped SLC caching implementation, nCache 4.0. It now comes with a hybrid SLC caching that's similar to Samsung’s TurboWrite but larger in capacity, much like we're accustomed to with SSDs powered by Phison’s latest controllers. The total dynamic SLC capacity spans roughly one-third of the available capacity (300GB on our 1TB sample) with a small and quick-to-recover static SLC cache (12GB on our 1TB sample) that's designed to provide the most performance and endurance.
With a multi-gear Low-Density Parity-Check (LDPC) ECC engine, RAID like protection for full multi-page recovery, internal SRAM ECC and end-to-end data path protection in its ECC scheme, along with the company over-provisioning the SSD by 9%, WD’s Black SN850 comes equipped with plenty of mechanisms to ensure your data is safe on the flash. WD backs the Black SN850 with a five-year warranty and rates it to endure up to 300 TB of writes per 500GB of capacity, or up to 1.2PB writes on the 2TB model.
We were able to quickly and securely wipe WD’s Black SN850 by initiating a secure erase from within our Asus X570 Crosshair VIII Hero (WiFi) motherboard’s UEFI. But, while it supports secure erase, the SSD lacks a now-common security feature that Samsung has supported on its drives for years – hardware-accelerated AES 256-bit full drive encryption. The Black SN850 does support both Trim and S.M.A.R.T. data reporting as well as Active State Power Management (ASPM), Autonomous Power State Transition (APST), and the PCIe L1.2 power state for low power draw at idle on mobile platforms, drawing only <5mW.
Software and Accessories
WD supports the Black SN850 with WD Dashboard, the company’s SSD toolbox that includes analysis tools, a firmware updater, and RGB lighting control on the heatsink model. WD also provides customers with Acronis True Image WD Edition for cloning and data backup.
A Closer Look
WD is tightlipped when it comes to revealing information about the hardware that powers the Black SN850 and didn't divulge many details about its next-gen controller when questioned. Still, we could deduce a few things based on the scraps and crumbs we were given.
From our external analysis, we can see the drive comes in an M.2 2280 single-sided form factor with an NVMe flash controller, a DRAM chip, and just two flash packages because of the large size of the controller package, measuring 17 x 17mm, taking up most of the PCB space.
To power the SSD, WD uses a proprietary Arm-based multi-core eight-channel PCIe 4.0 x4 NVMe SSD controller that leverages a Micron DDR4 DRAM chip to deliver responsive performance. WD references the controller as its WD_BLACK G2. Outfitting the WD Black SN850 with a faster Gen4 PHY is great for performance, but with such fast bandwidth, power draw and heat output were a concern at 28nm. Thus, like the controllers from competing manufacturers, WD opted to build the WD_BLACK G2 on a newer process node to better control those variables with TSMC’s 16nm FinFET technology.
WD paired the second-generation controller with the company’s newer Kioxia BiCS4 96L TLC flash operating at Toggle DDR3.0 speeds of 800 MTps. Both the 500GB and 1TB models leverage 256Gb dies while the 2TB leverages 512Gb dies. This flash has two planes (regions of independent access) for better performance than just a single plane, but it's not quite as fast as the company’s next-generation quad-plane BiCS5 112L flash that we will see become more prevalent next year. The new flash has twice the performance along with a Circuit Under Array (CUA) implementation.
In contrast to BiCS3, BiCS4 flash is not only faster thanks to a string-based start bias control scheme and smart Vt -tracking for improved reads, but has the benefit of improved efficiency over its predecessor with a low-pre-charge sense-amplifier bus scheme and sips down just 1.2V instead of 1.8V. WD’s Black SN850 leverages even-odd row decoding and shielded BL current sensing with this flash to enhance read throughput, too.
To scale the flash to new heights, the manufacturing process includes string-stacking two 48 wordline layer arrays on top of one another. While this is an easy way to increase cell array size, inefficiencies stem from additional circuitry, and wasted dummy layers. Concurrently, there is a risk of low yield due to stack misalignments. Scaling up to 96 wordline layers means using a total of 109 layers, including dummy gates and selectors in this instance, which is less efficient than Samsung’s V-NAND, which has yet to leverage string-stacking at up to 128 worldline layers (136 total layers).
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