Western Digital has rapidly risen to being a top-tier player in the market, and this is no more evident than with their newest high-end SSD, the WD Black SN850.

Less than a year after acquiring SanDisk, Western Digital began applying its performance-oriented WD Black branding to SSDs, starting with its first consumer NVMe drive. WD/SanDisk was late entering the consumer NVMe SSD market and its first product was not high-end by the standards of the time. With the second attempt, they got serious and designed their own NVMe SSD controllers, following the same strategy of vertical integration that has worked so well for market leader Samsung. The in-house controller had none of the bugs or performance problems that have plagued the first-generation controllers from most companies. That second-generation WD Black (internally designated SN700) immediately made Western Digital a major player in this market segment, but didn't quite put them at the top: it competed against the Samsung 960 EVO rather than the 960 PRO.

Now after learning some very valuable lessons from the SN700 and its minor refresh SN750, WD is back with the WD Black SN850, the first real hardware upgrade to the Black product line in over two years. Introduced last fall as part of the informal second wave of consumer PCIe 4.0 SSDs, the WD Black SN850 is aimed at the true top of the market, and is designed to compete against the Samsung 980 PRO and a multitude of more recent arrivals mostly based around the Phison E18 SSD controller.

WD Black SN850 Specifications
Capacity 500 GB 1 TB
2 TB
Form Factor M.2 2280 Single-sided
(Optional heatsink)
Interface NVMe PCIe 4.0 x4
Controller WD/SanDisk NVMe G2
NAND Flash Western Digital/SanDisk 96L 3D TLC
Sequential Read 7000 MB/s
Sequential Write 4100 MB/s 5300 MB/s 5100 MB/s
Random Read 800k IOPS 1M IOPS 1M IOPS
Random Write 570k IOPS 720k IOPS 710k IOPS
Warranty 5 years
Write Endurance 300 TB 600 TB 1200 TB
MSRP $119.99 $199.99 $379.99
(with heatsink+RGB) $169.99 $249.99 $469.99

Western Digital doesn't give us detailed performance specifications the way Samsung does, but the basic specifications make it clear that this drive is aimed at the very top: sequential reads up to 7GB/s are pushing the limits of the PCIe 4.0 x4 interface that is still catching on in the consumer market, and random reads at 1M IOPS from a single M.2 drive were just a dream a year ago. Overall, these peak performance specs line up pretty well with the Samsung 980 PRO: Samsung quotes higher random write performance, and WD quotes slightly faster sequential writes.

To reach this level of performance, Western Digital has introduced the second generation of their in-house NVMe SSD controller design. We don't have details of how this controller differs from their first-generation design, but it's a safe bet that almost every part of the chip was substantially upgraded. Compared to the preceding WD Black SN750, the SN850 also benefits from an upgrade to the NAND flash memory, from 64-layer to 96-layer TLC. Western Digital's client OEM SSD product line had already adopted the 96L TLC with the PC SN730, but their retail consumer Gen 3 drives didn't get a matching refresh.

Our review sample is the 1TB WD Black SN850, the capacity with the highest performance specifications. Western Digital sells the SN850 as either a standard M.2 SSD, or as an M.2 SSD with a heatsink and RGB lighting; we're testing the cheaper plain version. The stylized heatsink and RGB lighting adds a lot to the price tag, and we found that both the earlier WD Black SN750 and the competing Samsung 980 PRO perform fine without extra cooling, so we expect the SN850 with the heatsink to be solely a cosmetic upgrade.


The Competition: SSD vs SSD

The most important competitors for the SN850 are other PCIe 4.0 M.2 SSDs. We have results for both the Samsung 980 PRO and the Silicon Power US70 based on the older Phison E16 controller. Our 980 PRO results are using newer firmware than our initial review of that drive, and we've added results for the 2TB model alongside our 1TB results.

Western Digital SN850 1 TB PCIe 4.0 x4 In-House Gen 2
Samsung 980 Pro 1 TB
2 TB
PCIe 4.0 x4 Samsung
Silicon Power US70 1 TB PCIe 4.0 x4 Phison E16

Also of interest are two of the most premium SSDs from the PCIe 3.0 era: the 1.5TB Intel Optane SSD 905P and the Samsung 970 PRO. The 970 PRO was the last high-end consumer drive to use MLC NAND, which gave it a significant advantage on heavy, long-running storage workloads as compared with TLC SSDs that use SLC caching to provide improved peak performance. The 970 PRO is old enough that newer, faster TLC NAND is catching up even in tests where MLC used to be a major advantage—and of course the latest and greatest TLC drives with PCIe 4.0 have far higher peak performance.

Intel Optane SSD 905P 1.5 TB PCIe 3.0 x4 In-House
Samsung 970 PRO 1 TB PCIe 3.0 x4 Phoenix

On the PCIe 4.0 side, the Phison E18 controller is in a number of drives on the market as it was the first PCIe 4.0 NVMe controller to break cover in consumer-focused storage drives with better than PCIe 3.0 speed but not really testing the limits of PCIe 4.0 - plus it is known to be a toasty implementation. Due to a level of system maturity, to date we haven't tested an E18 drive, but our first Phison E18 SSD sample arrived yesterday. We're currently testing through it, especially with the latest firmware which fixes a few issues. That means that this review won't be able to declare an outright winner for the consumer SSD performance crown, but that's not a big deal. Just like when high-end SSDs were all bumping up against the limits of PCIe 3.0, small differences in benchmark scores between today's high-end PCIe 4.0 drives will not be noticeable during any normal real-world usage. These drives are already overkill for most purposes, and which one is technically the fastest is mostly a matter of bragging rights. Also on the market is the novel ADATA XPG Gammix S70 SSD with newcomer Innogrit's high-end SSD controller, which we have in hand but have not yet tested with the latest firmware.

Samsung 970 EVO Plus 1 TB PCIe 3.0 x4 Phoenix
Western Digital SN750 1 TB PCIe 3.0 x4 In-House Gen 1
Western Digital SN730 1 TB PCIe 3.0 x4 In-House Gen 1
Western Digital SN550 1 TB PCIe 3.0 x4 WD Custom (DRAMless)
SK hynix Gold P31 1 TB PCIe 3.0 x4 In House
Kingston KC2500 1 TB PCIe 3.0 x4 SM2262EN
Intel SSD 670p 1 TB PCIe 3.0 x4 SM2265

Representing the more mainstream parts of the consumer SSD market, we have several other Western Digital drives: the WD Black SN750 is the SN850's immediate predecessor, and the SN730 is the OEM counterpart with 96L NAND. The WD Blue SN550 is their second-generation entry-level NVMe SSD, and is one of the best DRAMless SSDs on the market. From other brands: The SK hynix Gold P31 is the current leader for power efficiency and provides performance that saturates its PCIe 3.0 interface. The Kingston KC2500 is one of the faster drives based around the popular Silicon Motion SM2262EN controller, and it uses the same 96L TLC as the SN850. The Intel SSD 670p is more of a low-end drive since it uses QLC NAND, but it's based on a very new generation of 3D NAND and a brand new controller from Silicon Motion which help it achieve great peak performance when using its SLC cache.

Read on over the next few pages for our full review of what ends up being a very speedy drive.

Trace Tests: AnandTech Storage Bench and PCMark 10
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  • Samus - Tuesday, March 23, 2021 - link

    eva: true. SATA hasn't been updated in over a decade (unlike SAS) and it'll be some time before consumer-class drives can saturate a 6Gbps link (currently almost none can even saturate a 3Gbps link.)

    With MAMR, HAMR, etc coming to market, performance is finally going to increase where areal density was historically the only way sequential transfers went up, so drives might start cracking SATA2 bandwidth. I suspect when drives near SATA3 bandwidth, it'll either be so long from now that hard disk technology in the consumer space will be dead (replaced by cheap NAND storage) as hard disk technology seems to be focusing on data centers where SAS is common and already capable of 12Gbps+, or consumers that wish to actually use magnetic disk storage will adopt SAS.
  • Molor1880 - Thursday, March 18, 2021 - link

    2.5 in drives and U.X won't make a comeback outside a server room, which is what that combination is designed for. The trend for personal devices is smaller and lighter, not bigger and bulkier. I would expect M.2 and gum stick drives to evolve, in step with PCIe, but it's not going away for at least another decade.
  • Tomatotech - Thursday, March 18, 2021 - link

    2.5” is dead for casual home use. I used to think it had a place in the office, but with the rise of laptop-powered WFH and the popularity of space-saving small SFF computers for the office I don’t see it as having a future.

    Your point about cost makes no sense. 2 TB+ of SSD chips is expensive. It makes no difference whether it’s on an m.2 stick or in a half empty U.3 case, it costs the same either way. With U.3 there’s a (small) extra cost for the packaging, plus the extra wires and extra ports required and extra assembly steps. Might be worth it in the datacentre but not for price-sensitive home or office market where 99% of drives are never swapped.
  • Tomatotech - Thursday, March 18, 2021 - link

    Ninja’d by Molor1880!
  • WaltC - Thursday, March 18, 2021 - link

    I think M.2 is here to stay. You are looking for economies of scale in NVMe M.2 drive capacity--that will happen as time goes on. It's remarkable to me how fast M.2 drives have ratcheted up in performance and capacity already. But, hey, if you need the economic capacity there's always the old 7200 rpm standby, right? These super-capacity drives will be around for a long while--but eventually M.2 will supplant them, imo.

    My older PCIe3 960 EVO M.2 boot drive would throttle regularly in large tasks, like doing a full AV Defender scan on C:\. The drive always crashed and never completed a full C:\ scan. This doesn't happen with the 980 Pro at all, and it's running in the same mboard and in the same slot the 960 ran in--using the same heatsink--just a flat sink that came with the mboard. Things are improving rapidly on the NVMe M.2 front, imo.
  • damianrobertjones - Friday, March 19, 2021 - link

    "Threw is the past tense of the verb throw. It’s the word you use to say that something threw you for a loop or threw you off. Through is an adverb and a preposition. It’s used to say that you entered on one side of something and exited on the other."

    Not sure if 2.5" drives have gone anywhere?
  • twotwotwo - Wednesday, April 21, 2021 - link

    There are a few 4 and 8TB m.2 drives out already, so a stick with more than 2TB might be practical for you before any switch to the mostly-enterprise u.3 form factor. Not that there's anything wrong with holding on to your current stuff! :)
  • Makaveli - Thursday, March 18, 2021 - link

    "Later this year we're expecting another wave of Phison E18 drives to arrive using 176L 3D TLC NAND"

    This is what i'm waiting to see.

    I don't like that all the new generation drives also all took a reduction in TBW and all seem to have smaller SLC caches minus this WD drive.
  • ozzuneoj86 - Thursday, March 18, 2021 - link

    With the SK Hynix P31 performing so well for the money, especially in efficiency, I'll be keeping an eye out for PCI-E 4.0 offerings from them.

    I'm currently booting from a 2.5" MX500 1TB. Since I have an X570 board, it feels like my next drive purchase should be PCI-E 4.0. Thankfully, I doubt these things provide any appreciable difference in performance over a good SATA SSD for the vast majority of applications I use, so I can stand to wait for the prices to come down. Given the choice between buying a 1TB SSD with blistering fast performance for $200, or one that generally benchmarks lower but uses less power, runs cooler and provides an almost identical experience for $135 (with sales often much lower)... its hard to justify the more expensive one.
  • lmcd - Thursday, March 18, 2021 - link

    Imo in a laptop it's impossible to justify a faster SSD that consumes more power.

    In a desktop, though, I can see it making sense for certain workloads.

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