WD Black SN850X 4 TB Review — Flagship Gen 4 NVMe
The WD Black SN850X 4 TB is Sandisk\xe2\x80\x99s flagship PCIe 4.0 NVMe in its largest single-sided-board era \xe2\x80\x94 four terabytes of TLC NAND with full top-tier speeds and a 2,400 TBW warranty.
The WD Black SN850X 4 TB is the second-largest capacity in Western Digital’s flagship Gen 4 NVMe family, built on the in-house SanDisk 20-82-20035 controller paired with Sandisk’s 112-layer BiCS5 3D TLC NAND and an LPDDR4 DRAM cache. At 4 TB the drive moves to a double-sided M.2 2280 PCB to fit eight TLC packages, with NAND chips on both faces and a 3.88 mm physical height — measurably thicker than the 2.38 mm single-sided 1 TB and 2 TB SKUs. Western Digital sells it in two variants: a bare double-sided PCB (WDS400T2X0E) and a heatsink version (WDS400T2XHE) with the larger 10.31 mm flagship heatsink.
The 4 TB is the volume capacity for serious creators and gamers who genuinely need the storage: Steam libraries with 30-plus AAA installs, multi-terabyte 4K and ProRes project archives, Plex / Jellyfin caches, and homelab scratch space. At this capacity the closest rivals are the Samsung 990 Pro 4 TB (TLC, in-house controller, similar Gen 4 ceiling), the Crucial T705 4 TB (PCIe 5.0, faster sequential but pricier and runs hotter), and the Crucial T500 4 TB (TLC, mainstream tier, lower street price). The SN850X 4 TB’s case is matching top-tier numbers with the 2 TB sibling but four times the capacity, and a 2,400 TBW endurance figure that puts it well above any QLC 4 TB drive.
For PS5 use the 4 TB has a caveat: the double-sided PCB and heatsink variant push toward the upper limit of Sony’s expansion-slot envelope. The heatsink SKU is the supported configuration and most users report it fits, but it is physically larger than the 1 TB and 2 TB heatsink versions. For a tight-tolerance PS5 install the 2 TB heatsink SKU is the safer pick.
✅ Storage Comparisons:
🚀 Performance and benchmarks
Sandisk rates the WD Black SN850X 4 TB at up to 7,300 MB/s sequential reads and 6,600 MB/s sequential writes on a PCIe 4.0 x4 link, with random IOPS of up to 1,200,000 reads and 1,100,000 writes — the same headline numbers as the 2 TB sibling. On real-world Windows benchmarks the 4 TB sits at the very top of Gen 4 drives, indistinguishable from the Samsung 990 Pro 4 TB on game-load tests and DirectStorage workloads, and well ahead of mainstream Gen 4 drives like the WD Black SN770 or Lexar NM790 on mixed random workloads.
Western Digital Black SN850X 4 TB vs M.2 4.0 x 4 peers
Switch between sequential throughput and random IOPS to see how this drive stacks up against other M.2 4.0 x 4 SSDs in our database. The highlighted bar is the drive on this page — click any other bar to open that drive.
- Patriot Viper PV593 1 TB: 14,500 MB/s read, 14,000 MB/s write
- Patriot Viper PV593 2 TB: 14,500 MB/s read, 14,000 MB/s write
- Patriot Viper PV593 4 TB: 14,500 MB/s read, 14,000 MB/s write
- Patriot Viper PV573 2 TB: 14,000 MB/s read, 12,000 MB/s write
- Western Digital Black SN850X 4 TB (this drive): 7,300 MB/s read, 6,600 MB/s write
The 4 TB capacity’s real advantage is sustained write behaviour. With twice the NAND of the 2 TB and four times the NAND of the 1 TB, the dynamic SLC cache is correspondingly larger, and independent reviewers consistently find that the 4 TB SN850X completes single-session 500-plus-gigabyte transfers largely inside the SLC region. Once the cache exhausts post-cache speeds settle into the 1.5 GB/s to 2 GB/s range, which is well above any DRAM-less HMB drive. For video editors writing multi-hundred-gigabyte project dumps in one continuous pour the 4 TB SN850X is the right tool inside the flagship tier, and the 8 TB sibling extends the SLC headroom further at the cost of slightly lower sequential read (7,200 MB/s).
🖥️ Endurance and warranty
Sandisk rates the WD Black SN850X 4 TB at 2,400 TBW (terabytes written) over a 5-year limited warranty, whichever limit is reached first. That is a top-tier TLC endurance figure for the 4 TB capacity — matching the Samsung 990 Pro 4 TB — and corresponds to roughly 1.3 TB of host writes every single day for the full five-year warranty period, vastly beyond what any gamer, creator, or homelab user generates in normal operation. At a more realistic 50 GB/day workload the rated 2,400 TBW corresponds to over 130 years of nominal life before the counter is exhausted. The TBW scales cleanly with capacity inside the family: 600 TBW at 1 TB, 1,200 TBW at 2 TB, and 4,800 TBW on the 8 TB headliner. Warranty service is handled directly via Sandisk RMA with proof of purchase, and the SANDISK Dashboard provides SMART monitoring and firmware updates on Windows.
📊 Specs
| Category | Value |
|---|---|
| Capacity [?] | 4 TB |
| Interface [?] | M.2 4.0 x 4 |
| Controller [?] | SanDisk 20-82-20035 |
| Memory type [?] | 112L Bics5 |
| DRAM [?] | LPDDR4 |
| Read speed (MB/s) [?] | 7300 |
| Write speed (MB/s) [?] | 6600 |
| Read IOPS [?] | 1200000 |
| Write IOPS [?] | 1100000 |
| Endurance (TBW) [?] | 2400 |
| MTBF (million hours) [?] | 2000000 |
| Warranty (years) [?] | 5 |
Conclusion
The WD Black SN850X 4 TB is the flagship pick for users who genuinely need four terabytes of top-tier PCIe 4.0 storage and want a DRAM-equipped TLC drive with a known controller and a credible 5-year, 2,400 TBW warranty. Skip it if 2 TB is enough for your workload, because the 2 TB SN850X delivers identical headline numbers at a much lower price; skip it again if you specifically need the absolute fastest sequential numbers, because a Crucial T705 4 TB on PCIe 5.0 will out-read it on supported platforms. The closest direct alternative is the Samsung 990 Pro 4 TB, which is functionally identical and usually decided by pricing on the day; the Crucial T500 4 TB is the cleaner step-down for users who do not need the absolute top tier. For a single-drive, high-capacity PCIe 4.0 build the SN850X 4 TB is one of the easiest premium recommendations.
+ Pros
- 7,300 MB/s sequential reads on PCIe 4.0
- 2,400 TBW endurance with 5-year warranty
- 4 TB capacity for large libraries and projects
- Large SLC cache holds sustained writes longer
- 1.2 million random read IOPS on tap
- Sandisk BiCS5 112-layer 3D TLC NAND
- Cons
- Double-sided PCB is thicker than smaller SKUs
- Premium pricing per gigabyte at 4 TB tier
- Heatsink SKU near PS5 envelope upper limit
- No PCIe 5.0 upgrade path at this capacity
- Adaptive thermal throttling under heavy loads
🛒 Buy this or similar SSD Storage:
✨ Video Review
WD Black SN850X SSD Review
