Burst IO Performance

Our burst IO tests operate at queue depth 1 and perform several short data transfers interspersed with idle time. The random read and write tests consist of 32 bursts of up to 64MB each. The sequential read and write tests use eight bursts of up to 128MB each. For more details, please see the overview of our 2021 Consumer SSD Benchmark Suite.

QD1 Burst IO Performance
Random Read Random Write
Sequential Read Sequential Write

The WD Black SN850 turns in excellent scores on almost all of the burst IO tests. For random reads, it edges out the Intel SSD 670p to set a new record for flash-based SSDs, and even when testing beyond the bounds of any possible SLC caching it is only 2% slower than the MLC-based Samsung 970 PRO. For random writes the WD Black SN850 is slightly slower than the Phison E16 drive, but otherwise is s clear step up in performance from the rest of the field. When testing sequential transfers on a small slice of the drive, the SN850 is substantially faster than everything else, but when testing across 80% of the drive its sequential read performance drops dramatically and is beat by the Samsung 980 PRO and several of the faster PCIe 3.0 drives.

Sustained IO Performance

Our sustained IO tests exercise a range of queue depths and transfer more data than the burst IO tests, but still have limits to keep the duration somewhat realistic. The primary scores we report are focused on the low queue depths that make up the bulk of consumer storage workloads. For more details, please see the overview of our 2021 Consumer SSD Benchmark Suite.

Sustained IO Performance
Random Read Throughput Power Efficiency
Random Write Throughput Power Efficiency
Sequential Read Throughput Power Efficiency
Sequential Write Throughput Power Efficiency

On the longer random read test, the WD Black SN850 doesn't quite stand out from the best performance offered by other drives with newer flash. But on the other three workloads the SN850 is clearly superior, with significant performance leads over the rest of the competition. Its power consumption is consistently on the high side and in some cases it is drawing more than any of the other drives, but the performance is high enough that the efficiency scores are all good.

Random Read
Random Write
Sequential Read
Sequential Write

For random reads, the SN850 eventually ramps up to around 4GB/s or 1M IOPS at the end of the test, which is significantly faster than any other drive that we've tested so far on this new test suite. However, when testing across 80% of the drive instead of just a 32GB slice, the random read performance falls to roughly the same level as the Samsung 980 PRO.

For random writes, the SN850's performance scales up a bit quicker than the 980 PRO, but it hits a throughput limit sooner and the 980 PRO ends up being much faster for random writes to the SLC cache at high queue depth.

For sequential reads, the SN850 ends up slightly faster than the 980 PRO, but when testing across 80% of the drive the Samsung reaches full performance with a lower queue depth. For sequential writes the SN850 is again a bit faster than the 980 PRO and this time it doesn't need higher queue depths to reach full speed, but it also starts running out of SLC cache before the test is over while the 980 PRO maintains full performance through the end of the test.

Random Read Latency

This test illustrates how drives with higher throughput don't always offer better IO latency and Quality of Service (QoS), and that latency often gets much worse when a drive is pushed to its limits. This test is more intense than real-world consumer workloads and the results can be a bit noisy, but large differences that show up clearly on a log scale plot are meaningful. For more details, please see the overview of our 2021 Consumer SSD Benchmark Suite.

The WD Black SN850 starts off this test with good random read latency, but around 80k IOPS it shifts gears and latency spikes alarmingly. It actually improves a few times later in the test so by the time the drive is approaching its throughput limit, it is only a bit slower than the Samsung 980 PRO.

Trace Tests: AnandTech Storage Bench and PCMark 10 Advanced Synthetic Tests: Block Sizes and Cache Size Effects


View All Comments

  • lmcd - Thursday, March 18, 2021 - link

    *a faster, but not substantially faster, SSD that consumes nearly 2x the power. Reply
  • ozzuneoj86 - Friday, March 19, 2021 - link

    Absolutely agree for laptops.

    For desktops, I think I'd need to see a review that measured thermals, overall system temperature and cooling noise as well as performance. Sure more performance is technically better, but if it is only noticeable in synthetic benchmarks (for now), adding several more watts of heat output to the area between your CPU and GPU isn't the best thing. Also, not having to worry as much about your SSD if ambient temps get a bit toasty is nice too.

    For the record, if prices were close I would still opt for more speed unless it was a really huge thermal\power penalty. At this point though, the $65-$90 (depending on sales) price difference is quite large. There's some wisdom in waiting for applications to start utilizing ultra high speed NVMe storage before investing extra money in it.

    Kind of like buying 64GB of RAM for future proofing. By the time you need it, RAM is faster and cheaper per GB.
  • artifex - Thursday, March 18, 2021 - link

    I'm hoping they'll make denser 3.0x4 offerings for the laptop space, especially if they can keep a lower power profile and decent thermals. I won't care about 4x4 until I'm upgrading to AM5 on my desktop, probably. Reply
  • Kamen Rider Blade - Thursday, March 18, 2021 - link

    All this review does is make me want Optane even more.

    That sheer utter consistency is what I'm looking for.

    And that sweet low latency.
  • Tomatotech - Thursday, March 18, 2021 - link

    Sadly Optane is dying. Micron has just abandoned 3D Xpoint, and Intel completely messed up their dual drives and most of the Optane range is MIA.

    This WD 850 gives you almost as much performance as Optane in the office or at home, at at a fraction of the price. There are other server orientated SSDs that are also becoming almost as good as Optane in the server space, again at far cheaper prices. It’s sad, I had high hopes for Optane but it seems Intel couldn’t scale it out.
  • ksec - Friday, March 19, 2021 - link

    And this Optane 905 isn't even that "great" so to speak. ( Even though it is very expensive, think of it as low cost Optane ) I want to see how Optane PX5800 perform.

    With that said, I am very suspired at the latency WD has managed to achieve. Even for Professional and enthusiast, it will be more than enough for 90+% of use case.
  • Spunjji - Friday, March 19, 2021 - link

    For what purpose? Reply
  • arashi - Sunday, March 21, 2021 - link

    Epeen. Reply
  • FatFlatulentGit - Thursday, March 18, 2021 - link

    No Sabrent Rocket 4 Plus in the benches? I'm baffled that it's not there seeing as how it's probably the most likely competitor for this drive. Reply
  • Billy Tallis - Thursday, March 18, 2021 - link

    As I mentioned in the article, my first Phison E18 drive arrived yesterday and I don't have complete results yet. But the first batch of results is in Bench: https://www.anandtech.com/bench/product/2732?vs=27... Reply

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