SK hynix is one of the major DRAM and NAND flash memory manufacturers, but for years they've had little to no presence in the retail consumer SSD market and have focused primarily on the OEM market. That started to change last year when they launched their Gold S31 SATA SSDs, but that wasn't really enough to establish SK hynix as an important brand for consumer SSDs. At CES in January, they previewed NVMe SSDs: the Gold P31 and Platinum P31.

When SK hynix PR reached out earlier this month to offer a review sample of the Gold P31 at short notice in advance of last week's launch, I was expecting a fairly straightforward review. Rushed review embargo periods are often a sign that the vendor doesn't want you to spend too much time digging into the details of the product, so I didn't expect the Gold P31 to stand out in any way from the crowd of other PCIe Gen3 NVMe SSDs already on the market. I was expecting that the most interesting facet of the Gold P31 would be the fact that SK hynix actually managed to be first to market with 128L NAND, after years of trying to run ahead of the competition in terms of 3D NAND layer count but with little success in following through in a timely fashion.

The 128L 3D NAND is an important accomplishment, but it turns out to have big consequences for more than just cost. The Gold P31 turned in the most surprising set of benchmark results I've seen, with power efficiency scores that seemed almost too good to be true (more on this later). SK hynix won't share quite as much technical information about these drives as we'd like to have, but they've shared enough to confirm that the Gold P31 does not fit the mold for a typical high-end consumer NVMe SSD.

The Gold P31 offers performance that is competitive with most other high-end consumer SSDs, but it achieves that performance with a very different strategy. For years, the standard formula for this product segment has been the use of TLC NAND with SLC caching, a controller with four lanes of PCIe 3.0 (and starting to move toward PCIe 4.0), DRAM in a ratio of 1 GB per 1TB of flash, and an eight-channel interface between the SSD controller and the NAND flash itself. It's that last piece that the Gold P31 changes, by using just four channels.

NAND Interface Speeds Matter Again

The SK hynix Gold P31 hits high-end performance targets with half the channels by using a much higher IO speed for those channels than we're used to. This NAND interface speed hasn't been an important factor in recent years because an 8 channel SSD can saturate a PCIe 3 x4 host connection with fairly pedestrian NAND interface speeds like 533MT/s. So even though NAND manufacturers and SSD controllers have been moving toward higher interface speeds, it has hardly mattered and has been much less interesting than talking about improvements in latency, power and density.

For the 64-layer 3D NAND generation, NAND interface speeds were typically in the 533-667MT/s range. The extremely popular Phison E12 controller supports up to 667MT/s, but SSDs using Toshiba (now Kioxia) 64L BiCS3 TLC at 533MT/s had no trouble offering good performance—usually only marginally slower than Silicon Motion's SM2262(EN) that supports up to 800MT/s. Now that the NAND market has moved to 96 layers and beyond, most NAND manufacturers can support speeds of 1.2GT/s (1200MT/s) or higher—but those speeds aren't a given. Just like DRAM, NAND chips can come in different speed grades, and not all SSD controllers can handle those speeds yet. SK hynix designs their own SSD controllers, and they updated their controller design to match the capabilities of their 128L NAND, running at 1.2GT/s. This provides plenty of headroom for a 4-channel SSD to saturate a PCIe 3.0 x4 link.

(Side note: The Sony PS5 will use a 12 channel controller, which means it should be able to hit its performance targets with a 533MT/s NAND interface speed. The Xbox Series X is likely using a 4-channel controller, so it will probably need to use a faster NAND interface speed despite the SSD as a whole offering less than half the throughput.)

We're used to seeing 4-channel NVMe SSDs as entry-level products. Those have mostly been using slower NAND interface speeds and offered peak throughput in the ballpark of just 2-2.5 GB/s, and the lower channel count has primarily been a cost-cutting measure (often paired with an elimination of the DRAM buffer to further reduce costs). The SK hynix controller used in the Gold P31 may be cheaper and smaller than the typical 8-channel PCIe gen3 NVMe controller, but it's designed to compete directly against them. SK hynix won't say whether the controller is built on the 28nm process that's used for most PCIe Gen3 NVMe controllers or if they've moved to a smaller FinFET-based node as we're seeing for almost all PCIE Gen4 controller designs. Either way, their controller starts off with a significant power advantage over larger 8-channel controllers.

SK Hynix Gold P31 SSD Specifications
Capacity 500 GB 1 TB
Form Factor M.2 2280 single-sided
Interface PCIe 3 x4 NVMe
Controller SK Hynix in-house
DRAM SK Hynix LPDDR4-4266
NAND Flash SK Hynix 128L 3D TLC
Sequential Read (128kB) 3500 MB/s
Sequential Write
SLC 3100 MB/s 3200 MB/s
TLC 950 MB/s 1700 MB/s
Random Read (4kB) SLC 570k
TLC 500k
Random Write (4kB) SLC 600k
TLC 220k 370k
Power Active 6.3 W
Idle < 50 mW
L1.2 Idle < 5 mW
Warranty 5 years
Write Endurance 500 TB
0.5 DWPD
750 TB
0.4 DWPD
MSRP $74.99

The SK hynix Gold P31 product line consists of just two capacities: 500GB and 1TB, with only the latter sampled for this review. The Platinum P31 that was announced at CES will be a 2TB model and we expect it to otherwise be identical to the Gold P31, but no further information about the Platinum P31 or its release date is available at this time. SK hynix provides fairly detailed performance specs for the Gold P31: we don't get the low queue depth ratings that matter most, but the high queue depth specs are broken down to show both SLC cache and post-cache TLC performance. The 500 GB model is rated for much lower TLC write speeds than the 1 TB model, but otherwise their performance ratings are similar and typical for a high-end PCIe gen3 drive.

The Gold P31 comes with better than average write endurance ratings: 500 TBW for the 500 GB model and 750 TBW for the 1TB model, putting them both above the standard 0.3 DWPD. Introductory pricing is fairly competitive at $75 and $135.


SK hynix won't confirm details about the NAND other than the layer count and the 1.2GT/s IO speed, but based on their previous announcements about their 128L 3D NAND we believe these are 1Tbit dies, each divided into four planes so they can offer comparable parallelism to 512Gbit dies that are only divided into two planes. (UPDATE: TechInsights insights is analyzing this flash, and it seems to be 512Gbit dies.) With their short-lived 96L generation, SK hynix adopted what they call a PuC: periphery under cell. This is basically the same idea as the Intel/Micron "CMOS under the Array" 3D NAND design, that moves most of the peripheral logic circuitry under the memory cell array, rather than alongside. This design has allowed Intel/Micron 3D NAND to achieve the smallest die sizes for a given layer count and die capacity. Now that SK hynix has adopted this and delivered a leading layer count, they should have one of the most cost-effective TLC parts on the market (provided they're getting good yields). The rest of the major NAND flash manufacturers have a similar technique on their roadmaps.

The Competition

For this review, we are primarily comparing the SK hynix Gold P31 against other high-end TLC-based NVMe drives. Some of these are drives using 64L NAND rather than 96L NAND because we have either been unable to get samples of the newer drives, or we haven't gotten around to testing them.  The high-end TLC drives included in this review are:

  • Samsung 970 EVO Plus: 92L TLC, same controller as original 970s
  • Kingston KC2000: SM2262EN + Toshiba/Kioxia 96L TLC, now replaced by the KC2500 with higher clock speeds
  • ADATA XPG SX8200 Pro: SM2262EN + Micron 64L TLC
  • Seagate FireCuda 510: Phison E12 + 64L TLC (newer version in the supply chain now uses 96L) and FireCuda 520: Phison E16 + 96L TLC, but restricted to PCIe gen3 on this testbed
  • WD Black SN750: High-end NVMe drive with 64L TLC. Until now, our benchmark for most efficient high-end NVMe drive
  • Toshiba (now Kioxia) XG6 - The first 96L consumer SSD (OEM only)

We have also included results from a few entry-level NVMe drives:

  • Toshiba (now Kioxia) BG4 - low-power DRAMless NVMe, 96L TLC
  • Intel 660p - 4-channel SM2263 controller with DRAM, 64L QLC (now replaced by 665p with 96L QLC)

The SK hynix Gold S31 and Samsung 860 EVO SATA drives also included for context.

AnandTech 2018 Consumer SSD Testbed
CPU Intel Xeon E3 1240 v5
Motherboard ASRock Fatal1ty E3V5 Performance Gaming/OC
Chipset Intel C232
Memory 4x 8GB G.SKILL Ripjaws DDR4-2400 CL15
Graphics AMD Radeon HD 5450, 1920x1200@60Hz
Software Windows 10 x64, version 1709
Linux kernel version 4.14, fio version 3.6
Spectre/Meltdown microcode and OS patches current as of May 2018
Cache Size Effects
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  • MrCommunistGen - Thursday, August 27, 2020 - link

    Truly impressive drive! I'm glad you were able to confirm that the power efficiency numbers held up and weren't the result of some kind of measurement error. When the Platinum P31 comes out I'll probably snag a 2TB model to upgrade my 1TB XG6 in my main ITX rig.

    Interesting that you mentioned the SN520. I needed a 2242 or 2230 SSD for a project I'm working on and was trying to decide between a BG4 and the SN520. I was able to refer to the previous Anandtech 1TB BG4 review but even then, I'm looking at either a 128GB or 256GB drive as that's what's available 2nd hand on eBay and the 1TB drive's performance isn't going to really represent the smaller drives.

    On the other hand I've found exactly nothing on the SN520.

    They're cheap enough so I decided to just buy one of each and test them both and see how they compare.
  • Luminar - Thursday, August 27, 2020 - link

    The 2280 form factor SN500s/SN520s are more common than the 2242s and 2230s.

    I would buy a 2280 SN520 and just Dremel it down to a 2242 form factor. It's been proven to work. As Anandtech wrote in their review, the electronics are only in the first 30mm of the PCB.
  • MrCommunistGen - Thursday, August 27, 2020 - link

    For the heck of it I decided to buy a bunch of different 2230 and 2242 SSDs on eBay to test. I was surprised to find 6 different models, 5 of which are from well-known brands. They all seem to be OEM drives pulled from laptops.

    I skipped any of the no-name, known garbage drives.
  • lilkwarrior - Thursday, August 27, 2020 - link

    Why was the 970 plus in the benchmarks, but not the 970 Pro?
  • MrCommunistGen - Thursday, August 27, 2020 - link

    If you really want to compare the performance of the P31 and the 970 Pro, you can look up the results in the "Bench" section of the website:

    To answer your question directly:
    I'd imagine that's because for a lot of client workloads the performance of the 970 Pro is relatively similar to the 970 EVO Plus. The Pro definitely has lower latency, particularly write latency -- but again -- in most client workloads that isn't going to translate into very noticeable differences.

    However, the Pro is SO much more expensive. Realistically, someone shopping for a fast consumer SSD who is looking at the P31 isn't going to also be considering the 970 Pro.

    FWIW, at the 1TB capacity the 970 Pro seems to be selling for ~$320, the 970 EVO Plus for ~$190, and the P31 for $135.

    If the idea is to compare to the highest performing non-volatile storage available today, that's probably what the Optane 905P results are for.
  • PaulHoule - Thursday, August 27, 2020 - link

    It is as if Taiyo Yuden started making writable DVD's under its own name.
  • nirolf - Friday, August 28, 2020 - link

    Ha ha! Good one!
  • jyotaro - Thursday, August 27, 2020 - link

    Any plans for a 500gb review of this product?
  • Billy Tallis - Thursday, August 27, 2020 - link

    Not at the moment. I'll try to get them to cough up a sample of that one when the Platinum P31 is released so I can compare across the full range of capacities, but I don't know how likely it is that they'll agree. This is still a pretty new relationship between us and SK hynix PR.
  • ozzuneoj86 - Thursday, August 27, 2020 - link

    Maybe I missed it, but does the high efficiency of this drive translate to significantly less heat output? Seems like it should. Some kind of thermal test would be useful for choosing a mobile SSD especially.

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