The Western Digital WD Black SN850 Review: A Very Fast PCIe 4.0 SSD
by Billy Tallis on March 18, 2021 12:50 PM ESTConclusion
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.
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Pinn - Thursday, March 18, 2021 - link
Would love to see thermals.JoeDuarte - Thursday, March 18, 2021 - link
Why are the write latencies so much lower than the read latencies? (For all the drives.) Is this normal for SSDs? I hadn't noticed this pattern before, or read anything about it. My assumption is that reading should be faster than writing.To really move the needle on latency we'll need to move away from PCIe to something like OpenCAPI, which is a much faster interface. Optane can't really stretch out to its full potential if it's going to be hitched to PCIe, even 4.0. With the end of Moore's Law, we really need to optimize the I/O as much as possible, and get rid of interfaces and buses that require many thousands of CPU cycles per transaction.
By the way, why is there no energy usage data for the Optane drive in the results? It seems to be missing for all benchmarks. That drive is in all the performance results except energy usage.
Billy Tallis - Thursday, March 18, 2021 - link
Reading a single page from NAND flash is a lot faster than programming a page. But writes can be cached and several smaller writes can be saved up to be issued in a batch that better uses the parallelism inside the SSD. So the amortized cost of writes can be much lower. Of course, this poses some risk to data in the event of power loss, but that's a generally-accepted tradeoff for consumer systems.The power data for the Optane 905P was left off because its idle power is higher than the peak load power of almost all of the other drives. There aren't a lot of interesting comparisons to be made there. The Optane drive is always the most power-hungry, by far. It would be even without the RGB LEDs. It only has a chance of being competitive on power efficiency for low-QD random reads.
Kamen Rider Blade - Friday, March 19, 2021 - link
Optane is so perfect as a home DeskTop OS drive where the low QD and latency really can be taken advantage of along with it's Random IO and Latency advantages.The vast majority of home users are 90/10 Read/Write.
Spunjji - Friday, March 19, 2021 - link
Only, for that usage, the price/capacity trade-off makes it poor value for money - and the advantages it does confer are barely noticeable in use.FunBunny2 - Friday, March 19, 2021 - link
"Optane is so perfect as a home DeskTop OS drive where the low QD and latency really can be taken advantage of"I would argue the opposite: Optane, et al, make the most sense for industrial strength RDBMS, used in App Mode.
Oxford Guy - Sunday, March 21, 2021 - link
'Of course, this poses some risk to data in the event of power loss, but that's a generally-accepted tradeoff for consumer systems.'Didn't some consumer SSDs have a capacitor to prevent data loss? Has that feature been lost due to the smaller form factor (versus SATA), or is it mainly due to cost-cutting?
Billy Tallis - Sunday, March 21, 2021 - link
There may have been a few "consumer" SSDs back in the very early days that had full power loss protection, but that has been an enterprise-only feature for as long as SSDs have been even remotely mainstream for consumers. (Exceptions: Intel 750 and Optane SSDs, which are re-branded enterprise drives and do have power loss protection.)There have been some consumer SSDs with partial power loss protection, designed to prevent data already on the drive from being corrupted by later writes that get interrupted by a power loss (but making no guarantees about completing any in-progress writes). This doesn't require extra capacitors for writes to SLC or any other single-pass writing (which includes a lot of TLC, if not all of it these days). And since there are also other good reasons not to leave a page in a partially-programmed state for long, I suspect most consumer SSDs have moved away from ever needing the kind of capacitor banks we saw on eg. early Crucial MX series drives.
Oxford Guy - Monday, March 22, 2021 - link
I can imagine that consumers who spends thousands on things like GPUs would be hard-pressed to pay for a capacitor.Good thing the flash drive companies are so watchful of our crucial pennies.
Mikewind Dale - Friday, March 26, 2021 - link
Does having a laptop battery or desktop UPS effectively take the place of power-loss capacitors on an SSD? I would think it does, but I'd like to be sure.