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WD Black SN850 1TB SSD Review

WD has been hard at work expanding its Black gaming and high-performance range of products. We recently looked at WD’s AN1500 add-in-card (review here) which delivered PCIe Gen 4-like speeds but over the PCIe Gen-3 interface. Now, with the Black SN850, we have WD’s first crack at a proper PCIe Gen 4 drive.

WD are in the fortunate position to have all three parts of the component jigsaw; NAND, controller and cache chip available in house so all three can be tuned to get the maximum out of any given drive. The SN850 uses WD’s G2 controller which is used in combination with BiCS4 96-layer 3D NAND.

WD quote Sequential read/write figures for the 1TB drive as up to 7,000MB/s and up to 5,300MB/s respectively. That 7,000MB/s read figure is the same for all three drives in the range. The entry-level 500GB is rated at 4,100MB/s for Sequential writes, while the 2TB is slightly slower than the 1TB drive at 5,100MB/s. Using the ATTO benchmark we couldn’t match those maximums, the tested drive producing a read figure of 6,510MB/s and a write figure of 4,840MB/s.

Even though we couldn’t match the official numbers those read and write ATTO results are the fastest we have seen to date for a PCIe Gen 4 drive. Using our own Sequential tests we could indeed confirm that 7,000MB/s rating as the tested drive produced a result of 7092.27MB/s. Again we couldn’t quite nail the maximum write figure but got a lot closer at 5,190.54MB/s.

As for random read performance, WD quote an up to 1,000,000 IOPS figure for the 1TB and 2TB drives (the 500GB drive is rated at up to 800,000 IOPS). Random writes are quoted as up to 570,000 IOPS for the 500GB drive, the 2TB drive at up to 710,000 IOPS with the 1TB drive fastest of the three at up to 720.000 IOPS.

We couldn’t get close to these figures with our 4-threaded tests. The best read figure we saw was 430,473 IOPS. We then retested the drive at a QD of 32 and with 16 threads which resulted in a figure of 742,492 IOPS, closer to the official figure but no cigar. Random writes came up short in our tests as well. Our 4-threaded test yielded 366,870 IOPS at a queue depth of 32. Staying at the same queue depth but increasing the thread count to 16 saw the resulting figure rise to 611,422 IOPS.

We may not have got close to the official random results but those QD32 figures for both reads and writes are the fastest we have seen to date from a PCIe Gen 4 drive.

As with all PCIe Gen 4 drives without a heatsink, the WD SN850 can get pretty hot when really pushed so it’s wise to make sure it has got some decent cooling.

The drive is also supported by the very good WD SSD Dashboard management software which includes a Gaming Mode. When turned on, the firmware disables the power saving features that are incorporated into the drive allowing lower latencies and more performance. The one annoying aspect of this Gaming Mode is that you have to restart the system to enable/disable it.

We found the 1TB WD Black SN850 available to order on Overclockers UK for £209.99 (inc VAT) HERE


  • Stunning performance.
  • WD Dashboard management utility.
  • 5-year warranty.


  • Couldn’t hit the maximum 4K figures under testing.

KitGuru says: Arriving seemingly from left field, WD’s entry into the PCIe Gen 4 market segment, with the Black SN850, has somewhat stolen the show.

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Rating: 9.0.

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