The Western Digital WD Black SN850 Review: A Very Fast PCIe 4.0 SSD
by Billy Tallis on March 18, 2021 12:50 PM ESTAdvanced Synthetic Tests
Our benchmark suite includes a variety of tests that are less about replicating any real-world IO patterns, and more about exposing the inner workings of a drive with narrowly-focused tests. Many of these tests will show exaggerated differences between drives, and for the most part that should not be taken as a sign that one drive will be drastically faster for real-world usage. These tests are about satisfying curiosity, and are not good measures of overall drive performance. For more details, please see the overview of our 2021 Consumer SSD Benchmark Suite.
Whole-Drive Fill
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On the first pass starting from an empty drive, the WD Black SN850's SLC cache handles sequential writes at a bit over 5GB/s and the cache lasts for about 281GB before running out. That's a very large SLC cache size for a TLC drive, which is probably why performance is so variable after the cache is full. For the second pass of sequential writes, the cache size has been reduced to about 20GB, but the drive shows a second burst of 20GB of SLC-speed writes later in the test.
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| Average Throughput for last 16 GB | Overall Average Throughput | ||||||||
The aggressive SLC caching behavior on the SN850 comes at the cost of slower and less-consistent post-cache write performance, but Western Digital's earlier WD Black SSDs already behaved quite well here. The SN850 manages to keep write speed from ever dropping below 1GB/s, and the overall average across the entire drive fill is basically the same as the SN730, the OEM relative to the SN750 but with the same newer flash as the SN850.
On the second sequential write pass when the SN850's variable-size SLC cache is already at its smallest, post-cache performance is extremely consistent and faster than any other TLC SSD we have tested, but still 15% slower than the MLC-based Samsung 970 PRO.
Working Set Size
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Most high-end drives have boring and steady results on this test since they don't skimp on DRAM. The QD1 random read latency for the SN850 is better than any other TLC drive we've tested, and only 4% slower than the MLC-based Samsung 970 PRO.
Performance vs Block Size
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The WD Black SN850 is strongly optimized for 4kB IOs, with lower IOPS and throughput for sub-4kB block sizes on all four workloads. None of the other drives show such broad preferences for 4kB block sizes, but some of Western Digital's drives and a few others show this behavior on at least some of the workloads. This tuning pays off in some places, such as the SN850's leading random write performance for small block sizes (which is followed by the SLC cache running out while testing larger block random writes). There are some other weaknesses including poor performance for small-block sequential reads, but more importantly it has great performance for sequential reads with larger block sizes.
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lmcd - Thursday, March 18, 2021 - link
*a faster, but not substantially faster, SSD that consumes nearly 2x the power.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.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?arashi - Sunday, March 21, 2021 - link
Epeen.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.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...