Western Digital WD Black SN850X

Launched in May 2022, the Western Digital WD Black SN850X is an NVMe solid-state drive (SSD) in the high-end segment, designed for workstations and gaming setups. An 8TB variant was added in July 2024.

It is a direct successor to the WD Black SN850 as Western Digital's flagship consumer PCIe 4.0 storage solution and a competitor of SSDs such as the Samsung 990 Pro and other flagship Gen4 drives. The SN850X features sequential read speeds up to 7,300 MB/s and write speeds up to 6,600 MB/s in its optimal configurations.

An optional heatsink is available for select capacities (a requirement to meet the minimum recommended specs for Sony's PlayStation 5).

Specifications

Manufacturer's Datasheet

Controller

The SN850X uses Western Digital's proprietary 8-channel controller manufactured on an 8nm process node. For 1-4TB models, the controller is designated as 20-82-20035-B2 (Black G2), while the 8TB variant uses the 20-82-000292-B2 (Triton Mp16+ B) controller. This in-house design builds on the original SN850's controller and offers improved performance and thermal efficiency.

Cache

The drive features DDR4 DRAM cache for mapping table storage, with Micron D9XPG modules providing 16Gb (2GB) of cache memory. Additionally, the SN850X uses dynamic pseudo-SLC (pSLC) caching strategy with the following characteristics:

• 1TB model: ~300GB pSLC cache, 1,500 MB/s sustained write after cache exhaustion
• 2TB model: ~600GB pSLC cache, 1,500 MB/s sustained write after cache exhaustion
• 4TB model: ~1,200GB pSLC cache, 1,500 MB/s sustained write after cache exhaustion
• 8TB model: ~2,350GB pSLC cache, 2,850 MB/s sustained write after cache exhaustion

NAND Type and Specifications

As the 8 TB model of the SN850X was launched much later, the NAND configuration depends on capacity.

• 1 TB-4 TB models: 112-layer BiCS5 3D TLC NAND (manufactured by Kioxia/SanDisk joint venture)
• 8 TB model: 162-layer BiCS6 3D TLC NAND

The newer BiCS6 in the 8TB model offers improved density and efficiency. Both NAND types provide similar endurance ratings (between 1,700-3,000 program/erase cycles for).

Power Consumption

Power consumption specifications vary by capacity and workload. It peaks at up to 9W peak but is typically 6-7W during sustained workloads. Active idle power is ~1W, low-power state (PS3) is 250mW, and sleep state (PS4) is 5mW.

These numbers translate to improved thermal efficiency compared to its predecessor, with reviewers noting operating temperatures substantially lower than the original SN850 under similar workloads.

Write Endurance and Over-Provisioning

Western Digital rates the SN850X with the following Total Bytes Written (TBW) endurance ratings:

• 1TB: 600 TBW
• 2TB: 1,200 TBW
• 4TB: 2,400 TBW
• 8TB: 4,800 TBW

The drives include factory over-provisioning of approximately 7-10% beyond the advertised capacity (the difference between raw NAND capacity and user-accessible space).

Other Noteworthy Features

The SN850X introduces Game Mode 2.0, an enhancement over the original Game Mode found in earlier WD Black drives. This includes automatic game detection and optimization, predictive loading algorithms (that pre-cache anticipated game data), and disabled low-power states for improved responsiveness.