The Western Digital WD Black SN850 Review: A Very Fast PCIe 4.0 SSDby Billy Tallis on March 18, 2021 12:50 PM EST
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
|Form Factor||M.2 2280 Single-sided
|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|
|Write Endurance||300 TB||600 TB||1200 TB|
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
|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.
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Pinn - Thursday, March 18, 2021 - linkWould love to see thermals.
JoeDuarte - Thursday, March 18, 2021 - linkWhy 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 - linkReading 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 - linkOptane 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 - linkOnly, 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 - linkThere 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 - linkI 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 - linkDoes 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.