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 (Reviewed)	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 Elpis
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.

AnandTech Storage Bench - The Destroyer

Our AnandTech Storage Bench tests are traces (recordings) of real-world IO patterns that are replayed onto the drives under test. The Destroyer is the longest and most difficult phase of our consumer SSD test suite. For more details, please see the overview of our 2021 Consumer SSD Benchmark Suite.

Average Data Rate
Average Latency	Average Read Latency	Average Write Latency
99th Percentile Latency	99th Percentile Read Latency	99th Percentile Write Latency
Energy Usage

The WD Black SN850 starts off with very impressive performance on The Destroyer: only 7.5% slower overall than the Optane 905P and almost twice the overall performance of the Samsung 980 PRO, which is seriously underperforming on this test. The SN850 has great latency scores all around, including for 99th percentile latencies. The SN850 isn't as energy-efficient as Western Digital's PCIe 3.0 SSDs, but is substantially better than the 980 PRO or the Phison E16-based Silicon Power US70.

AnandTech Storage Bench - Heavy

The ATSB Heavy test is much shorter overall than The Destroyer, but is still fairly write-intensive. We run this test twice: first on a mostly-empty drive, and again on a completely full drive to show the worst-case performance.

Average Data Rate
Average Latency	Average Read Latency	Average Write Latency
99th Percentile Latency	99th Percentile Read Latency	99th Percentile Write Latency
Energy Usage

On the Heavy test, the WD Black SN850 again comes in second place for overall performance, behind the Optane 905P. Its lead over the other PCIe 4.0 drives is smaller and the 980 PRO surpasses it in some of the latency metrics, but overall the differences between the SN850 and the 980 PRO would seldom be noticeable to the end-user during this kind of heavy workload. The SN850 again has a clear energy efficiency lead over the other PCIe 4.0 drives.

AnandTech Storage Bench - Light

The ATSB Light test represents ordinary everyday usage that doesn't put much strain on a SSD. Low queue depths, short bursts of IO and a short overall test duration mean this should be easy for any SSD. But running it a second time on a full drive shows how even storage-light workloads can be affected by SSD performance degradation.

Average Data Rate
Average Latency	Average Read Latency	Average Write Latency
99th Percentile Latency	99th Percentile Read Latency	99th Percentile Write Latency
Energy Usage

The WD Black SN850 is tied for first place when the Light test is run on an empty drive, but its full-drive performance is better than any of the other drives except the Optane SSD. The latency scores are all top-notch, though the 99th percentile read latency is a bit higher than the other PCIe 4.0 SSDs. As with the other ATSB tests, the SN850 uses less energy than the other PCIe 4.0 drives, but isn't as efficient as some of the good PCIe 3.0 SSDs.

PCMark 10 Storage Benchmarks

The PCMark 10 Storage benchmarks are IO trace based tests similar to our own ATSB tests. For more details, please see the overview of our 2021 Consumer SSD Benchmark Suite.

Full System Drive	Overall Score	Average Bandwidth	Average Latency
Quick System Drive	Overall Score	Average Bandwidth	Average Latency
Data Drive	Overall Score	Average Bandwidth	Average Latency

The WD Black SN850 has a clear lead over other flash-based SSDs in all three PCMark 10 Storage tests. It has a larger SLC cache than most 1TB drives, and it's just large enough to contain all the writes from these tests. The SN850 beats even the higher-capacity drives because its cache is faster than most in addition to being large. The SN850 comes closest to matching the Optane SSD's performance on the Data Drive test that focuses relatively more on sequential IO, where the SN850 offers twice the throughput of the Optane 905P.

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.

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.

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	WD Black SN850 1TBSamsung 870 EVO 1TBSamsung 970 EVO Plus 1TBSamsung 970 PRO 1TBSamsung 980 PRO 1TBSamsung 980 PRO 2TBKingston KC2500 1TBIntel SSD 670p 2TBSK hynix Gold P31 1TBWD Blue SN550 1TBWestern Digital SN730 1TBWD Black SN750 1TBSilicon Power US70 1TBIntel Optane SSD 905P 1.5TB
Random Write	WD Black SN850 1TBSamsung 870 EVO 1TBSamsung 970 EVO Plus 1TBSamsung 970 PRO 1TBSamsung 980 PRO 1TBSamsung 980 PRO 2TBKingston KC2500 1TBIntel SSD 670p 2TBSK hynix Gold P31 1TBWD Blue SN550 1TBWestern Digital SN730 1TBWD Black SN750 1TBSilicon Power US70 1TBIntel Optane SSD 905P 1.5TB
Sequential Read	WD Black SN850 1TBSamsung 870 EVO 1TBSamsung 970 EVO Plus 1TBSamsung 970 PRO 1TBSamsung 980 PRO 1TBSamsung 980 PRO 2TBKingston KC2500 1TBIntel SSD 670p 2TBSK hynix Gold P31 1TBWD Blue SN550 1TBWestern Digital SN730 1TBWD Black SN750 1TBSilicon Power US70 1TBIntel Optane SSD 905P 1.5TB
Sequential Write	WD Black SN850 1TBSamsung 870 EVO 1TBSamsung 970 EVO Plus 1TBSamsung 970 PRO 1TBSamsung 980 PRO 1TBSamsung 980 PRO 2TBKingston KC2500 1TBIntel SSD 670p 2TBSK hynix Gold P31 1TBWD Blue SN550 1TBWestern Digital SN730 1TBWD Black SN750 1TBSilicon Power US70 1TBIntel Optane SSD 905P 1.5TB

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.

WD Black SN850 1TBSamsung 870 EVO 1TBSamsung 970 EVO Plus 1TBSamsung 970 PRO 1TBSamsung 980 PRO 1TBSamsung 980 PRO 2TBKingston KC2500 1TBIntel SSD 670p 2TBSK hynix Gold P31 1TBWD Blue SN550 1TBWestern Digital SN730 1TBWD Black SN750 1TBSilicon Power US70 1TBIntel Optane SSD 905P 1.5TB

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.

Advanced 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

Pass 1	WD Black SN850 1TBSamsung 870 EVO 1TBSamsung 970 EVO Plus 1TBSamsung 970 PRO 1TBSamsung 980 PRO 1TBSamsung 980 PRO 2TBKingston KC2500 1TBIntel SSD 670p 2TBSK hynix Gold P31 1TBWD Blue SN550 1TBWestern Digital SN730 1TBWD Black SN750 1TBSilicon Power US70 1TBIntel Optane SSD 905P 1.5TB
Pass 2	WD Black SN850 1TBSamsung 870 EVO 1TBSamsung 970 EVO Plus 1TBSamsung 970 PRO 1TBSamsung 980 PRO 1TBSamsung 980 PRO 2TBKingston KC2500 1TBIntel SSD 670p 2TBSK hynix Gold P31 1TBWD Blue SN550 1TBWestern Digital SN730 1TBWD Black SN750 1TBSilicon Power US70 1TBIntel Optane SSD 905P 1.5TB

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.

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

WD Black SN850 1TBSamsung 870 EVO 1TBSamsung 970 EVO Plus 1TBSamsung 970 PRO 1TBSamsung 980 PRO 1TBSamsung 980 PRO 2TBKingston KC2500 1TBIntel SSD 670p 2TBSK hynix Gold P31 1TBWD Blue SN550 1TBWestern Digital SN730 1TBWD Black SN750 1TBSilicon Power US70 1TBIntel Optane SSD 905P 1.5TB

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

Random Read	WD Black SN850 1TBSamsung 870 EVO 1TBSamsung 970 EVO Plus 1TBSamsung 970 PRO 1TBSamsung 980 PRO 1TBSamsung 980 PRO 2TBKingston KC2500 1TBIntel SSD 670p 2TBSK hynix Gold P31 1TBWD Blue SN550 1TBWestern Digital SN730 1TBWD Black SN750 1TBSilicon Power US70 1TBIntel Optane SSD 905P 1.5TB
Random Write	WD Black SN850 1TBSamsung 870 EVO 1TBSamsung 970 EVO Plus 1TBSamsung 970 PRO 1TBSamsung 980 PRO 1TBSamsung 980 PRO 2TBKingston KC2500 1TBIntel SSD 670p 2TBSK hynix Gold P31 1TBWD Blue SN550 1TBWestern Digital SN730 1TBWD Black SN750 1TBSilicon Power US70 1TBIntel Optane SSD 905P 1.5TB
Sequential Read	WD Black SN850 1TBSamsung 870 EVO 1TBSamsung 970 EVO Plus 1TBSamsung 970 PRO 1TBSamsung 980 PRO 1TBSamsung 980 PRO 2TBKingston KC2500 1TBIntel SSD 670p 2TBSK hynix Gold P31 1TBWD Blue SN550 1TBWestern Digital SN730 1TBWD Black SN750 1TBSilicon Power US70 1TBIntel Optane SSD 905P 1.5TB
Sequential Write	WD Black SN850 1TBSamsung 870 EVO 1TBSamsung 970 EVO Plus 1TBSamsung 970 PRO 1TBSamsung 980 PRO 1TBSamsung 980 PRO 2TBKingston KC2500 1TBIntel SSD 670p 2TBSK hynix Gold P31 1TBWD Blue SN550 1TBWestern Digital SN730 1TBWD Black SN750 1TBSilicon Power US70 1TBIntel Optane SSD 905P 1.5TB

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.

Mixed IO Performance

For details on our mixed IO tests, please see the overview of our 2021 Consumer SSD Benchmark Suite.

Mixed Random IO	Throughput	Power	Efficiency
Mixed Sequential IO	Throughput	Power	Efficiency

The WD Black SN850's overall performance on the mixed random IO test is just behind the Samsung 980 PRO, but still very good for a flash-based SSD. However, its power efficiency on that test is only second-tier, behind the 980 PRO and the SK hynix Gold P31.

On the mixed sequential IO test, the SN850's performance is better than any of the 1TB drives, and almost as fast as the 2TB 980 PRO. It's still not quite as efficient as the 980 PRO and during this test it averages about 6.6W, which is definitely getting up to where a heatsink would be of use (for similarly long-running workloads).

Mixed Random IO	WD Black SN850 1TBSamsung 870 EVO 1TBSamsung 970 EVO Plus 1TBSamsung 970 PRO 1TBSamsung 980 PRO 1TBSamsung 980 PRO 2TBKingston KC2500 1TBIntel SSD 670p 2TBSK hynix Gold P31 1TBWD Blue SN550 1TBWestern Digital SN730 1TBWD Black SN750 1TBSilicon Power US70 1TBIntel Optane SSD 905P 1.5TB
Mixed Sequential IO	WD Black SN850 1TBSamsung 870 EVO 1TBSamsung 970 EVO Plus 1TBSamsung 970 PRO 1TBSamsung 980 PRO 1TBSamsung 980 PRO 2TBKingston KC2500 1TBIntel SSD 670p 2TBSK hynix Gold P31 1TBWD Blue SN550 1TBWestern Digital SN730 1TBWD Black SN750 1TBSilicon Power US70 1TBIntel Optane SSD 905P 1.5TB

On the mixed random IO test, the SN850 starts out with a lead over the 980 PRO for the most read-oriented mixes but then the 980 PRO takes a small lead for the rest of the test while always using less power. On the mixed sequential IO test, it seems like the larger SLC cache may be helping the SN850 get a performance boost relatively early while there are still more reads than writes, and it maintains leading performance as the mix gets more write-heavy. That means the SN850 ends up having a considerable performance advantage over the 1TB 980 PRO for a 50/50 mix that would be expected from a workload like copying files within the same SSD.

 

Power Management Features

Real-world client storage workloads leave SSDs idle most of the time, so the active power measurements presented earlier in this review only account for a small part of what determines a drive's suitability for battery-powered use. Especially under light use, the power efficiency of a SSD is determined mostly be how well it can save power when idle.

For many NVMe SSDs, the closely related matter of thermal management can also be important. M.2 SSDs can concentrate a lot of power in a very small space. They may also be used in locations with high ambient temperatures and poor cooling, such as tucked under a GPU on a desktop motherboard, or in a poorly-ventilated notebook.

WD Black SN850 1TB NVMe Power and Thermal Management Features
Controller	WD/SanDisk NVMe G2
Firmware	611100WD
NVMe Version	Feature	Status
1.0	Number of operational (active) power states	3
1.1	Number of non-operational (idle) power states	2
	Autonomous Power State Transition (APST)	Supported
1.2	Warning Temperature	84 °C
	Critical Temperature	88 °C
1.3	Host Controlled Thermal Management	Supported
	Non-Operational Power State Permissive Mode	Supported

The WD Black SN850 implements the full range of power and thermal management features. It's specced for quick transitions in and out of its low-power sleep states. The drive indicates that it may use up to 9 W while active; it probably gets close at peak, but the highest sustained power draw we saw during our synthetic benchmarks was in the 7-8W range. Constraining this drive to either of its lower-power active states would definitely throttle performance by a lot.

WD Black SN850 1TB NVMe Power States
Controller	WD/SanDisk NVMe G2
Firmware	611100WD
Power State	Maximum Power	Active/Idle	Entry Latency	Exit Latency
PS 0	9.0 W	Active	-	-
PS 1	4.1 W	Active	-	-
PS 2	3.5 W	Active	-	-
PS 3	25 mW	Idle	5 ms	10 ms
PS 4	5 mW	Idle	5 ms	45 ms

Note that the above tables reflect only the information provided by the drive to the OS. The power and latency numbers are often very conservative estimates, but they are what the OS uses to determine which idle states to use and how long to wait before dropping to a deeper idle state.

Idle Power Measurement

SATA SSDs are tested with SATA link power management disabled to measure their active idle power draw, and with it enabled for the deeper idle power consumption score and the idle wake-up latency test. Our testbed, like any ordinary desktop system, cannot trigger the deepest DevSleep idle state.

Idle power management for NVMe SSDs is far more complicated than for SATA SSDs. NVMe SSDs can support several different idle power states, and through the Autonomous Power State Transition (APST) feature the operating system can set a drive's policy for when to drop down to a lower power state. There is typically a tradeoff in that lower-power states take longer to enter and wake up from, so the choice about what power states to use may differ for desktop and notebooks, and depending on which NVMe driver is in use. Additionally, there are multiple degrees of PCIe link power savings possible through Active State Power Management (APSM).

We report three idle power measurements. Active idle is representative of a typical desktop, where none of the advanced PCIe link or NVMe power saving features are enabled and the drive is immediately ready to process new commands. Our Desktop Idle number represents what can usually be expected from a desktop system that is configured to enable SATA link power management, PCIe ASPM and NVMe APST, but where the lowest PCIe L1.2 link power states are not available. The Laptop Idle number represents the maximum power savings possible with all the NVMe and PCIe power management features in use—usually the default for a battery-powered system but rarely achievable on a desktop even after changing BIOS and OS settings. Since we don't have a way to enable SATA DevSleep on any of our testbeds, SATA drives are omitted from the Laptop Idle charts.

Typically for Western Digital's NVMe controllers, the active idle power consumption from the SN850 is high at over 1W, and the desktop idle state only drops that by 35%. But the SN850's deepest idle state gets power draw down to the appropriate range for use in a laptop. Wakeup from the desktop idle state is almost instant, but waking up from the deepest idle is quite a bit slower than on Samsung's drives. The SN850 still wakes up several milliseconds faster than indicated by its firmware, and it's not slow enough to be a serious concern for system responsiveness.

Conclusion

The Western Digital WD Black SN850 has clearly established itself as a premium consumer SSD. It trades the lead with the Samsung 980 PRO on many tests but beats Samsung more often than not, making the WD Black SN850 the fastest PCIe 4.0 SSD we have tested so far.

Western Digital was slow to get into the NVMe game and at times it has seemed like they weren't trying very hard to go after the high end. But they're definitely serious contenders now. The high-end consumer SSD market is no longer just Samsung and the runners-up.

Overall the SN850 does have a few performance quirks, but no serious weaknesses to worry about. The SN850 has a bigger and faster SLC cache than most of the competition and generally seems better-optimized for client workloads than the 980 PRO.

The SN850 also tends to have a bit better power efficiency than the 980 PRO, though the SN850 can definitely end up drawing a lot of power to deliver such high performance. Western Digital has sacrificed some of the efficiency from their previous-generation drives, so the heatsink option makes more sense than it did for the SN750. But the heatsink should be no means be viewed as mandatory. Only the most intense niche workloads will be able to keep the SN850 busy long enough for thermal throttling to become a serious limitation.

Samsung and Western Digital are also facing stiff competition from numerous brands that are using the Phison E18 SSD controller. We don't have full benchmark results from any of those yet, but preliminary results indicate that while there may be no clear winner for the absolute fastest consumer SSD, the Western Digital SN850 is holding on to most of its individual benchmark wins. Later this year we're expecting another wave of Phison E18 drives to arrive using 176L 3D TLC NAND, which may shift the balance.

Some enthusiasts have bemoaned the switch away from MLC NAND (2 bits per cell) for high-end drives. But the WD Black SN850 shows that high-end TLC (3 bits per cell) drives now match or surpass the performance of the Samsung 970 PRO on almost every single metric, even the corner cases where the TLC+SLC caching strategy traditionally runs into trouble. The only remaining test where that last high-end MLC drive still has a significant advantage is sustained sequential write speed after any SLC cache has been filled. For the very narrow range of workloads where that might matter more than the significantly higher peak performance modern consumer TLC drives offer, there are plenty of enterprise TLC drives that don't use SLC caching at all.

MLC is now dead, and there's no compelling reason to bring it back (except for niche applications).

Premium NVMe SSD Price Comparison March 18, 2021
	500 GB	1 TB	2 TB	4 TB
WD Black SN850 (without heatsink)	$119.99 (24¢/GB)	$199.74 (20¢/GB)	$379.99 (19¢/GB)
ADATA XPG Gammix S70		$199.99 (20¢/GB)	$399.99 (20¢/GB)
Corsair MP600 PRO (Phison E18)		$224.99 (22¢/GB)	$434.99 (22¢/GB)
Sabrent Rocket 4 Plus (Phison E18)		$199.99 (20¢/GB)	$399.98 (20¢/GB)	$799.99 (20¢/GB)
Samsung 980 PRO	$119.99 (24¢/GB)	$196.74 (20¢/GB)	$379.99 (19¢/GB)
Inland Performance (Phison E16)	$94.99 (19¢/GB)	$178.99 (18¢/GB)	$329.99 (16¢/GB)
Sabrent Rocket 4.0 (Phison E16)	$89.99 (18¢/GB)	$149.98 (15¢/GB)	$299.98 (15¢/GB)
PCIe 3.0:
SK hynix Gold P31	$74.99 (15¢/GB)	$134.99 (13¢/GB)
WD Black SN750	$62.99 (13¢/GB)	$138.08 (14¢/GB)	$299.99 (15¢/GB)
Samsung 970 EVO Plus	$79.99 (16¢/GB)	$164.99 (16¢/GB)	$319.99 (16¢/GB)

The top-tier PCIe 4.0 SSDs are all priced very similarly right now, accurately reflecting that they all provide about the same real-world performance. Western Digital's current pricing for the WD Black SN850 is definitely competitive in this context. For a lot of consumers shopping in this segment, the decision may come down to heatsink options and aesthetics. The older, somewhat slower and less efficient generation of PCIe 4.0 SSDs based on the Phison E16 controller includes some much more affordable drives that are only a bit more expensive than the top PCIe 3.0 SSDs.

For most use cases a PCIe 4.0 SSD is still definitely overkill as it won't offer meaningfully better real-world performance than a good PCIe 3.0 SSD. PCIe 4.0 SSDs are still largely lacking their killer app, and saving something like $65 on a 1TB drive to drop down to PCIe 3.0 definitely has an impact on the rest of a system build's budget. But for consumers that are convinced they have good reason to upgrade to PCIe 4.0 storage, the WD Black SN850 is worthy choice. It offers the satisfaction and bragging rights of one of the fastest drives available, and will not be significantly outclassed until PCIe 5.0 arrives.