Specifications
Model
Ultastar DC SN861 (WUS6BA138PSP9X3)
Capacity
3.84 TB
Form Factor
2.5-inch U.2, 15 mm
Interface
PCIe Gen5 x4, NVMe 2.0
NAND
BiCS6 3D TLC
Sequential Read
Up to 13,700 MB/s (128 KiB)
Sequential Write
Up to 6,800 MB/s (128 KiB)
Random Read
Up to 3,300K IOPS (4 KiB)
Random Write
Up to 600K IOPS (4 KiB)
Endurance
1 DWPD (read-intensive)
Security
TCG Opal 2.01, ISE, SE
Power Loss Protection
Full PLP
MTBF
2.5 million hours
UBER
< 1 sector per 10^17 bits read
Operating Temperature
0 °C to 70 °C (case)
Warranty
5-year limited
Target Workload
Hyperscale, cloud, AI data pipeline, CDN
Overview
The Ultrastar DC SN861 is Western Digital's first PCIe Gen5 data-centre SSD family, built on BiCS6 TLC NAND with a Gen5 controller that doubles the per-drive host bandwidth of the previous Gen4 generation. At 3.84 TB the WUS6BA138PSP9X3 sits in the sweet spot for read-intensive server deployments: enough capacity for cache and hot tiering without paying the per-terabyte premium of the 7.68 TB and 15.36 TB points.
The family is available in both U.2 and E1.S form factors. U.2 15 mm suits standard 2.5-inch hot-swap bays in mainstream rack servers, while the same drive in E1.S targets denser hyperscale chassis where 15 mm U.2 will not fit. Selection of SE / ISE / TCG Opal 2.01 security variants lets an operator standardise on self-encrypting drives across a fleet.
For AI infrastructure specifically, the SN861 is used as a high-queue-depth read tier feeding GPU hosts — the 3,300K IOPS read figure is what matters there, since training and inference data pipelines are overwhelmingly read-dominated. QS Compute supplies the SN861 in volume with factory-sealed packaging and serialised warranty.
Key Benefits
Gen5 host bandwidth without Gen5 prices — 13,700 MB/s read over PCIe Gen5 x4 while remaining backward-compatible with Gen4 slots. Read-optimised endurance — 1 DWPD over five years suits caching, CDN and AI pipeline tiers. Fleet-grade security — SE, ISE and TCG Opal 2.01 variants allow one security standard across a mixed server estate.
Applications
Hyperscale and cloud read tiers, AI/ML data pipelines feeding GPU hosts, CDN edge caches, scale-out NAS and object storage, and general-purpose virtualisation datastores where read bandwidth is the binding constraint.
Request a Quote — WD ULTRASTAR DC SN861 3.84TB — PCIE GEN5 U.2 NVME SSD (WUS6BA138PSP9X3)
QS Compute — global B2B supply of AI computing hardware, edge AI systems and accelerators. Volume pricing, 15-day sample lead time.
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