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

  • Oxford Guy - Monday, March 22, 2021 - link

    What am I going to do about it? Tell the truth, aka whinge. Reply
  • Beaver M. - Friday, March 19, 2021 - link

    I heard reports that WD SSDs cant do Windows sleep, which is a reason why Samsung did their own NVMe driver. Can you confirm that? Reply
  • Endgame124 - Friday, March 19, 2021 - link

    What this review really says is we need less TLC drives, and either flat out all SLC drives or a new revision of the Optaine 905P. Reply
  • Oxford Guy - Sunday, March 21, 2021 - link

    SLC shouldn't be so drastically faster than TLC if MLC is not.

    So, if the data does indeed suggest what you're saying then it suggests that Samsung's implementation of MLC is lacking. MLC should be between SLC and TLC in performance, not 'dead' (equivalent to TLC).
  • MS - Sunday, March 21, 2021 - link

    I appreciate the idle power numbers but they are really meaningless. Why don't you show sequential and random write power consumption which should be in the 25 to 40 W range. Until the drive starts heating up and the performance collapses as a consequence of thermal throttling. Anything else is, er, marketing collateral at best Reply
  • Billy Tallis - Sunday, March 21, 2021 - link

    What are you talking about? The power numbers reported here are for the drive itself, not the whole computer system's wall power consumption. Even the Optane SSD included in this review doesn't hit 25W, let alone 40W. M.2 drives rarely break 8W. SATA SSD usually stay under 5W. And the idle power numbers are not at all meaningless; consumer SSDs spend the overwhelming majority of their time idle. Reply
  • kumataro - Thursday, March 25, 2021 - link

    So the SN850 is faster when it is brand new and has > 80% free space... once the drive starts to get full the Samsung 980 Pro has better performance? Reply
  • 529th - Sunday, April 11, 2021 - link

    Just picked up a SN850, and the model number is WDBAPY0010BNC, however it was advertised as the model in this review, the WDS100T1X0E. What did I just buy?

    I've seen articles about companies changing part revisions that are not as fast as the ones sent out for reviews.
  • mrplus - Wednesday, April 14, 2021 - link

    Hi, guys, lame question – does this pci-4 thing means that I need a new pci-4-friendly controller to use it? Or it’s just completely internal matter and any - for example - pci-friendly-usb3.2 external case will work with it? Reply
  • Billy Tallis - Thursday, April 29, 2021 - link

    PCIe is backwards-compatible: the host and the device will negotiate the highest link speed and widest lane count that are supported by both end points. So a Gen4 SSD in a motherboard that only supports Gen3 will work fine, limited to Gen3 speeds. A Gen4 SSD in a USB to NVMe enclosure that only provides PCIe Gen3 x2 to the drive will likewise be compatible, but with severely crippled performance. Reply

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