Western Digital May Introduce Penta Layer Cell (PLC) NAND by 2025

[Raevenlord]

Western Digital has apparently delayed the introduction of Penta Layer Cell (PLC) NAND-based flash to 2025. The company had already disclosed development on the technology back in 2019, around the same time that Toshiba announced it (Toshiba which is now Kioxia, and a Western Digital partner in the development of the technology). The information was disclosed at Bank of America Merrill Lynch 2021 Global Technology Conference, where Western Digital's technology and strategy chief Siva Sivaram said that "I expect that transition [from QLC to PLC] will be slower. So maybe in the second half of this decade we are going to see some segments starting to get 5 bits per cell."

PLC is another density-increase step for NAND flash, whereby each NAND cell can have five bits written into it, thus increasing the amount of information available in the same NAND footprint. To achieve these 5 bits, each cell must store one of 32 voltage states, which in turn inform the flash controller of which corresponding data bits are stored herein. Siva Sivaram said that he expect the technology to take some more time to mature than most, due to the need for controller development that can take advantage of the increased density while making up for the shortcoming in this increased bit-per-cell approach (lower endurance and lower performance). PLC won't bring us HDD-tier storage density by itself (it only enables storage of 25% more data per cell); however, when paired with increasing layers of NAND flash, those 25% extra quickly add up.



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[Nuckles56]

Oh good, that means you'll be able to fill up the drive twice and then you'll have worn out the drives. I hope they price this really cheaply then...

 

[Midland Dog]

maybe these ics will finally kill bulk hdd storage. if you only need to write the data once and then read it forever your all goods

 

[TumbleGeorge]

maybe these ics will finally kill bulk hdd storage. if you only need to write the data once and then read it forever your all goods

Yes 5 bit per cell and 5 times rewrite. Back step:
a) SLC - Many PBW
b) MLC - Small PBW or many TBW
c) TLC - Many TBW or average TBW
d) QLC - Average TBW or small TBW
e) PLC - Small TBW(not GBW only because in years from 2025+ will not be produced SSD's with below of 1TB volume)
f) NextLC - below 1 write per cell

 

[claster17]

Given how QLC drives are barely any cheaper than TLC, I don't see how PLC can compete even without looking at its downsides.

 

[BSim500]

I'm holding out for HLC (Hex Layer). With just 1x PE cycle, we'll finally have a "Write Once Read Many" replacement for optical -R media...

 

[Tomorrow]

How about fixing QLC first (price mostly) before moving on? They managed to get TLC to the point where it's perfectly ok but QLC has been dragging it's feet for years now with less than stellar results and TLC level prices. Even when it has been cheaper it has not been enough to offset the loss in endurance or performance to really make much sense.

Mark my words when i say that the future is not QLC, PLC etc. The future is adding more layers to TLC. Samsung has said they believe it scales to ~1000L and are set to indroduce 176L this year.
Adding more layers means cheaper, faster and bigger TLC drives. Perhaps this will drag QLC along to the point that it will actually be acceptable at some point but i wont hold my breath.

 

[john_]

I guess WD's plan is to transform SSDs to HDDs in performance while also throwing their reliability from a cliff. That way they can get back into building even more HDDs without the help of Chia.
I mean, if QLC is something to avoid, what can we expect from PLC?

 

[BSim500]

How about fixing QLC first (price mostly) before moving on? They managed to get TLC to the point where it's perfectly ok but QLC has been dragging it's feet for years now with less than stellar results and TLC level prices. Even when it has been cheaper it has not been enough to offset the loss in endurance or performance to really make much sense.

I don't think QLC / PLC, etc, can be "fixed". SSD's peaked at MLC (sustained writes) and TLC (general usage) simply because of the nature of flash memory:-

SLC (1 bit) = 100% vs 0

MLC (2 bit) = 100% vs 66% vs 33% vs 0

TLC (3 bit) = 100% vs 86% vs 71% vs 57% vs 43% vs 28% vs 14% vs 0

QLC (4 bit) = 100% vs 93% vs 87% vs 80% vs 73% vs 67% vs 60% vs 53% vs 47% vs 40% vs 33% vs 27% vs 20% vs 13% vs 7% vs 0%

PLC (5 bit) = 100% vs 97% vs 94% vs 90% vs 87% vs 84% vs 81% vs 77% vs 74% vs 71% vs 68% vs 65% vs 61% vs 58% vs 55% vs 52% vs 48% vs 45% vs 42% vs 39% vs 35% vs 32% vs 29% vs 26% vs 23% vs 19% vs 16% vs 13% vs 9% vs 6% vs 3% vs 0%

Drive durability has fallen through the floor 11x since MLC (if the voltage for PLC based drives drifts as little as 3% (vs 33% MLC) the data changes / gets corrupted). We only got away with TLC due to using SLC cache + more advanced ECC to hide their own issues vs MLC but those were "one shot" improvements. There's no "magic beans" equivalent for QLC / PLC as all such workarounds are maxed out now. Despite the usual tech site click-bait of "HDD's are dead", I wouldn't touch these with a barge pole for any offline / cold storage / external drive backup likely to remain unpowered for any length of time. I still find it shocking that no tech site is bothering to test unpowered data retention of modern drives on the grounds of "we did one article on that back in 2013 and found no problems, so that's that" whilst ignoring that the "1 year data retention" standard was based off several year old MLC based Intel drives with relatively large +20nm cell sizes and an awful lot has changed since then...

 

[Maxx]

This was already known, since FMS 2020 in the least where TechInsights showed PLC starting around 2026 with the possibility extending all the way to OLC (octal- or 8-level cell). I've covered split-gate and split-cell technology - which was published under Kioxia's name - since last year as well, which enables QLC and PLC to exceed current limitations. See below for links to both sources.

How about fixing QLC first (price mostly) before moving on? They managed to get TLC to the point where it's perfectly ok but QLC has been dragging it's feet for years now with less than stellar results and TLC level prices. Even when it has been cheaper it has not been enough to offset the loss in endurance or performance to really make much sense.

Mark my words when i say that the future is not QLC, PLC etc. The future is adding more layers to TLC. Samsung has said they believe it scales to ~1000L and are set to indroduce 176L this year.
Adding more layers means cheaper, faster and bigger TLC drives. Perhaps this will drag QLC along to the point that it will actually be acceptable at some point but i wont hold my breath.

QLC was never expected to reach decent market penetration (and thus cost) until 2024 at the earliest. These estimates go back years...

QLC actually has a lot going for it moving forward. For one, it gives the flexibility of pSLC and pMLC modes but also pTLC. Kioxia's QLC already supports simultaneous pSLC and pTLC modes, and I've tracked the latter as being just as fast as their native TLC. QLC is also the basis of X-NAND which I covered extensively, because of the math. If your physical page size is 16 kB, logical page size 4kB, and of course 16 kB data/page buffers, then splitting it into 4 is quite convenient, or 4x4, again as seen with X-NAND. To put it simply, QLC is binary in levels (e.g. 2^2) which makes such things simpler. See source below.

QLC also benefits more from floating gate as with Intel's 144L QLC. There's a reason nobody else really makes good QLC, outside possibly Samsung, although they have struggled as well. Split-gate technology is especially robust with FG designs. And here again you can use FG for TLC, but it makes much more sense to risk it with SG using QLC due to its 4-bit nature. And then you can run that in pTLC mode of course. I don't need to remind people that the Plotripper Pro is probably QLC in pSLC mode...because it's evenly divisible and cheaper.

Drive durability has fallen through the floor 11x since MLC (if the voltage for PLC based drives drifts as little as 3% (vs 33% MLC) the data changes / gets corrupted). We only got away with TLC due to using SLC cache + more advanced ECC to hide their own issues vs MLC but those were "one shot" improvements. There's no "magic beans" equivalent for QLC / PLC as all such workarounds are maxed out now. Despite the usual tech site click-bait of "HDD's are dead", I wouldn't touch these with a barge pole for any offline / cold storage / external drive backup likely to remain unpowered for any length of time. I still find it shocking that no tech site is bothering to test unpowered data retention of modern drives on the grounds of "we did one article on that back in 2013 and found no problems, so that's that" whilst ignoring that the "1 year data retention" standard was based off several year old MLC based Intel drives with relatively large +20nm cell sizes and an awful lot has changed since then...

Arguably. Intel's 64L QLC achieved 1000 P/E while at 96L it could get up to 1500 P/E. Micron's TLC in the same architecture was 1500 P/E (64L) but up to 3000 P/E (B27B) although more commonly 2000 P/E (B27A). Of course, Micron moved to replacement gate which has much higher endurance at the baseline, but that's not what we're comparing here. See below for a source.

QLC has been surprisingly robust with floating gate and this is liable to remain the case, given Intel's 144L QLC and Kioxia's split-gate research (for QLC and PLC). FG with SG may actually be "magic beans" due to the shape of the cells - you get natural isolation and electromagnetic shielding. See the SG source for more on this.

In general, 3D NAND is superior to 2D/planar in retention, simply because the process node is so much larger (that is why they moved to 3D). 3D flash has more possible sources of disturb (i.e. there's X, Y, and XY disturb) but they are much less impactful (more isolation between cells). There's also a ton of ways to mitigate it (more "magic beans" if you prefer) - I've covered these extensively on my discord if you want the technical aspects. Now of course you're talking about power-off retention which fits JEDEC testing (at a given temperature) and I can't argue with you on cold storage as that remains a possible issue here. And you're right, old SLC/MLC drives could retain data for a decade but things have changed. Although I question the relevance even in the enterprise space due to how QLC tends to be used (it's not for long-term cold storage).

---

Some sources:

3D Semicircular Flash Memory Cell: Novel Split-Gate Technology to Boost Bit Density

3D NAND: Current, Future, and Beyond

X-NAND: New Flash Architecture Combines QLC Density with SLC Speed

A Closer Look at Micron 3D NAND Features

 

[theeldest]

Given how QLC drives are barely any cheaper than TLC, I don't see how PLC can compete even without looking at its downsides.

QLC is cheaper, just not so much directly for enthusiast buyers. OEMs are getting cheaper devices which help them reduce costs and maybe pass that on to end buyers. Hyper scale customers (like AWS, Google, FB, etc) get QLC cheaper than TLC because they're buying at scale.

PLC (and beyond) will mostly go to the big buyers. It'll be available for us to buy but we're not the intended audience.

I don't think QLC / PLC, etc, can be "fixed". SSD's peaked at MLC (sustained writes) and TLC (general usage) simply because of the nature of flash memory:-
<snip>

Drive durability has fallen through the floor 11x since MLC (if the voltage for PLC based drives drifts as little as 3% (vs 33% MLC) the data changes / gets corrupted). We only got away with TLC due to using SLC cache + more advanced ECC to hide their own issues vs MLC but those were "one shot" improvements. There's no "magic beans" equivalent for QLC / PLC as all such workarounds are maxed out now. Despite the usual tech site click-bait of "HDD's are dead", I wouldn't touch these with a barge pole for any offline / cold storage / external drive backup likely to remain unpowered for any length of time. I still find it shocking that no tech site is bothering to test unpowered data retention of modern drives on the grounds of "we did one article on that back in 2013 and found no problems, so that's that" whilst ignoring that the "1 year data retention" standard was based off several year old MLC based Intel drives with relatively large +20nm cell sizes and an awful lot has changed since then...

Drive durability has gone up. What's come down is the amount of over provisioning and endurance for consumer drives. And it's not because they're worse it's because manufacturers have a better understanding of how much endurance is actually needed.

If you need a high endurance device they still exist but they're the 'enterprise' versions. The TLC enterprise devices don't use SLC cache, they're just fast on their own. Look at the Samsung PM1733. It's a 3.84TB read intensive drive with 7 petabytes of endurance.

And regarding your last statement of 1 year data retention being based off relatively large 20nm cell sizes, current 3D cell sizes are ~40nm. Since NAND is scaling through layer increases they were able to go waaay up in cell size and still increase density. It'll be a while before we're going back down in cell size as there is quite a bit of room to scale layers and it's more cost effective to do so.


EDIT: Read what Maxx said above. He smart.

 

[chrcoluk]

It is just getting silly now, what they will get maybe extra 5-10% margin for this but for a vastly inferior product.

I can see it now 2025 announcement, "vendor adds 8th layer to NAND, an extra whopping 12.5% capacity, but dont worry it still allows 20 erase cycles and can write faster than 5meg/sec in SLC cache".

 

[Tomorrow]

QLC was never expected to reach decent market penetration (and thus cost) until 2024 at the earliest. These estimates go back years...

Fancy tech but none of wich benefits the consumer in terms of price, capacity or performance. And by 2024 we will already have something better.
QLC has failed.

 

[XiGMAKiD]

*looks at my SSD*
You've been the goodest boye so far, please stay alive at least for the next 2 or 3 decade

 

[Wirko]

I'm holding out for HLC (Hex Layer). With just 1x PE cycle, we'll finally have a "Write Once Read Many" replacement for optical -R media...

That would be perfectly acceptable for the majority of terabytes hoarded - at the right price AND large capacity AND long retention. However, and pardon my bad English, something's telling me that we're going to get the right price NAND large capacity NAND long retention.

 

[bug]

Yeah no, I think I'll hold on till I can get 2TB per cell NAND

 

[Maxx]

Fancy tech but none of wich benefits the consumer in terms of price, capacity or performance. And by 2024 we will already have something better.
QLC has failed.

What? QLC is the dominating type of flash in enterprise moving forward. This is one reason it's lagging in the consumer market (demand) but there are other reasons, however analysts didn't expect it to have 1/3rd market share until 2024, and this was as predicted in 2019. Also the new Intel DC drives are not real TLC, they are Intel's 144L QLC in pTLC mode. Lastly, if you read my source above for split-gate technology, which Kioxia has been exploring in addition to PLC, their testing is for QLC. Saying QLC will be replaced when TLC is currently still dominating in the consumer space makes no sense. (PCM/memristor tech is way far off and is not going to be prevalent in the consumer space outside of maybe embedded)

Hyper scale customers (like AWS, Google, FB, etc) get QLC cheaper than TLC because they're buying at scale.

Right, QLC is huge in enterprise, just look at FMS 2020. There are some limitations in scaling (the prominent manufacturer, Intel, is still on FG) and Intel invested a lot to dig out QLC market share in the consumer space (which led to them getting their NAND bought by SK hynix). It's still got a way to go but we're seeing novel uses of QLC (FuzeDrive, Plotripper Pro) and some popular high-capacity drives (Rocket Q/Q4, 870 QVO), plus in the OEM space (H10/H20, and 660p/665p/670p). QLC in hybrid pSLC/pTLC mode is also very interesting but still rare (Kioxia's 96L QLC uses this). SG offers a way forward but is still years off. But I don't think anybody expected QLC to overtake TLC in the consumer space in the short-term.

 

[theeldest]

What? QLC is the dominating type of flash in enterprise moving forward. This is one reason it's lagging in the consumer market (demand) but there are other reasons, however analysts didn't expect it to have 1/3rd market share until 2024, and this was as predicted in 2019. Also the new Intel DC drives are not real TLC, they are Intel's 144L QLC in pTLC mode. Lastly, if you read my source above for split-gate technology, which Kioxia has been exploring in addition to PLC, their testing is for QLC. Saying QLC will be replaced when TLC is currently still dominating in the consumer space makes no sense. (PCM/memristor tech is way far off and is not going to be prevalent in the consumer space outside of maybe embedded)



Right, QLC is huge in enterprise, just look at FMS 2020. There are some limitations in scaling (the prominent manufacturer, Intel, is still on FG) and Intel invested a lot to dig out QLC market share in the consumer space (which led to them getting their NAND bought by SK hynix). It's still got a way to go but we're seeing novel uses of QLC (FuzeDrive, Plotripper Pro) and some popular high-capacity drives (Rocket Q/Q4, 870 QVO), plus in the OEM space (H10/H20, and 660p/665p/670p). QLC in hybrid pSLC/pTLC mode is also very interesting but still rare (Kioxia's 96L QLC uses this). SG offers a way forward but is still years off. But I don't think anybody expected QLC to overtake TLC in the consumer space in the short-term.

One of the other big drivers (moving forward) for QLC (and above) will be ZNS (zoned namespaces). It'll require relatively significant software development investments to use but this is fine for hyper scale and big enterprise.

For those unfamiliar, ZNS effectively puts the onus on the application to manage the Flash Translation Layer (FTL). The host needs to do all writes sequentially with no modification of data. This means that there is no write amplification so the 2000 P/E cycles translate to nearly 2000 drive fills whereas current drives when full and doing lots of garbage collection can suffer as high as 10x - 15x. This means that as far as spec sheets are concerned that 2,000 P/E cycles NAND is limited to ~150 drive fills.

ZNS will enable QLC/PLC/HLC and beyond for large users (FB, Google, Amazon, etc) that can tune their software to optimally use NAND devices (sequential writes, random reads).

Is your boot drive going to get cheaper because of this? No. Will online storage get cheaper? Yup.

 

[Wirko]

How about fixing QLC first (price mostly) before moving on? They managed to get TLC to the point where it's perfectly ok but QLC has been dragging it's feet for years now with less than stellar results and TLC level prices. Even when it has been cheaper it has not been enough to offset the loss in endurance or performance to really make much sense.

Mark my words when i say that the future is not QLC, PLC etc. The future is adding more layers to TLC. Samsung has said they believe it scales to ~1000L and are set to indroduce 176L this year.
Adding more layers means cheaper, faster and bigger TLC drives. Perhaps this will drag QLC along to the point that it will actually be acceptable at some point but i wont hold my breath.

Adding layers has its own challenges and is not progressing fast. It sure looks simple if you're looking at those nice drawings and microscope images. In reality, all the vertical holes need to be etched/drilled to have perfectly uniform diameter from top to bottom and be perfectly straight and exactly vertical, so they can connect all the cells in a column.

1000-layers-high stacks (1000 layers on one die, not a stack of dies) may become viable one day or not, it's a matter of economics, like most things in chip manufacturing.

Semi Engineering has a good and long article on that.

 

[theeldest]

Adding layers has its own challenges and is not progressing fast. It sure looks simple if you're looking at those nice drawings and microscope images. In reality, all the vertical holes need to be etched/drilled to have perfectly uniform diameter from top to bottom and be perfectly straight and exactly vertical, so they can connect all the cells in a column.

1000-layers-high stacks may become viable one day or not, it's a matter of economics, like most things in chip manufacturing.

Semi Engineering has a good and long article on that.

True to a point.

My point of layers vs cell size is that even with the hurdles of scaling layers it's still a better / more cost-effective path forward. And it's not just scaling up layers that you can etch through. Stacking is used by all the manufacturers now and offers a way to again scale layers without the individual etch needing to scale at the same rate.

 

[Minus Infinity]

Oh dear god, the egineering to reliably discrminate 32 discrete voltage levels will be insane. This should never be a thing, ever. It'll be 2025 before QLC is worth buying IMO.

 

[Tomorrow]

What? QLC is the dominating type of flash in enterprise moving forward. This is one reason it's lagging in the consumer market (demand) but there are other reasons, however analysts didn't expect it to have 1/3rd market share until 2024, and this was as predicted in 2019. Also the new Intel DC drives are not real TLC, they are Intel's 144L QLC in pTLC mode. Lastly, if you read my source above for split-gate technology, which Kioxia has been exploring in addition to PLC, their testing is for QLC. Saying QLC will be replaced when TLC is currently still dominating in the consumer space makes no sense. (PCM/memristor tech is way far off and is not going to be prevalent in the consumer space outside of maybe embedded)

Enterprise is just one segment of the market. The fact that a technlogy dominates or is well suited for one market does not mean it can achieve wide market penetration.
Also im not sure what enterprise segment are you looking at but the ones i have had contact with always go with high endurance. Even if it means paying insane $ per GB like Optane.

As for Intel SSD's: contacts that i have in enterprise space say they will never again buy an Intel SSD due to absurdly high failiure rate. Atleast when it comes to QLC. Optane is very reliable tho.

Adding layers has its own challenges and is not progressing fast.

Still faster than increasing bits per cell. In 13 years (2008, Intel X-25) we have gone from SLC > MLC > TLC > QLC. That is 3 jumps. Layer count has increased by 6 times from first 3D NAND in 2013 that was 24 layer to 176 layer this year. That is 8 years and 6 times increase compared to 13 years and 3 times increase. Nearly double the increase in half the time. It's pretty clear that manufacturers are at a limit already with QLC and no one knows if PLC will even be viable. Where as stacking layers still leaves plenty of room for progress.

 

[Maxx]

Enterprise is just one segment of the market. The fact that a technlogy dominates or is well suited for one market does not mean it can achieve wide market penetration.
Also im not sure what enterprise segment are you looking at but the ones i have had contact with always go with high endurance. Even if it means paying insane $ per GB like Optane.

As for Intel SSD's: contacts that i have in enterprise space say they will never again buy an Intel SSD due to absurdly high failiure rate. Atleast when it comes to QLC. Optane is very reliable tho.

Still faster than increasing bits per cell. In 13 years (2008, Intel X-25) we have gone from SLC > MLC > TLC > QLC. That is 3 jumps. Layer count has increased by 6 times from first 3D NAND in 2013 that was 24 layer to 176 layer this year. That is 8 years and 6 times increase compared to 13 years and 3 times increase. Nearly double the increase in half the time. It's pretty clear that manufacturers are at a limit already with QLC and no one knows if PLC will even be viable. Where as stacking layers still leaves plenty of room for progress.

Again, go back through FMS 2020. QLC is expected to surpass 50% of bits by 2025 in that space. A significant number of presentations focused on getting the most out of QLC, and for good reason. For example, IBM had "beating TLC with QLC." I've included one of their presentations and 3 others related to the topic here.

Intel surpassed 10 million QLC SSDs. Last year. In February. You underestimate the volume massively.

Jeongdong Choe covers the future of NAND for TechInsights. In his presentation (p. 10) he shows we'll have PLC around 2026 with viability all the way up to OLC (octal-level cell) through the use of Through Silicon Via (TSV), package on package (PoPoP), high bandwidth NAND (HBN, listed as HBM on his chart), etc. I have an article here that covers some of this technology.

I've already explained how PLC will do well with ample sources, but to reiterate, Kioxia's article has a figure that shows you just how good PLC would be with a semicircular floating gate architecture (b) as compared to the normal circular charge trap for QLC (a, right side):

ZNS will enable QLC/PLC/HLC and beyond for large users (FB, Google, Amazon, etc) that can tune their software to optimally use NAND devices (sequential writes, random reads).

Yep, ZNS as based on SMR is the way forward. The new NVMe specification is having enterprise move away from open channel SSDs precepts and towards zoned namespaces. With ZNS the traditional concerns of SSDs (and thus, QLC+) are mitigated. Covered here for those that want to know more.

Adding layers has its own challenges and is not progressing fast. It sure looks simple if you're looking at those nice drawings and microscope images. In reality, all the vertical holes need to be etched/drilled to have perfectly uniform diameter from top to bottom and be perfectly straight and exactly vertical, so they can connect all the cells in a column.

There are a ton of challenges with it, not least the fact you're dealing with more decks over time since maintaining aspect ratio of memory holes/pillars is impossible. Layers will of course continue to increase but several technologies will be required to reach those lofty limits. Also, more layers is not a substitute for more bits; there's a reason nobody is making 3D 2-bit MLC, for example.

Oh dear god, the egineering to reliably discrminate 32 discrete voltage levels will be insane. This should never be a thing, ever. It'll be 2025 before QLC is worth buying IMO.

Check my image just above. It's scary, but not as bad as you think thanks to some innovative techniques.

 

[Tomorrow]

Again, go back through FMS 2020. QLC is expected to surpass 50% of bits by 2025 in that space. A significant number of presentations focused on getting the most out of QLC, and for good reason. For example, IBM had "beating TLC with QLC." I've included one of their presentations and 3 others related to the topic here.

Intel surpassed 10 million QLC SSDs. Last year. In February. You underestimate the volume massively.

Expected being the word. Analysts have been wrong before. 10 million since 2018 does not seem that impressive. Atleast not without numbers from other manufacturers to compare to.

 

[theeldest]

Expected being the word. Analysts have been wrong before. 10 million since 2018 does not seem that impressive. Atleast not without numbers from other manufacturers to compare to.

SSD Market Share | T4

The Solid State Drive - SSD Market had 320 million unit shipments in 2020 and is forecast to grow by 13% in 2021. Samsung is the SSD Market Share leader with a 28% share in 2019. See more in-depth SSD Statistics and data below.

www.t4.ai

• Intel is 8% of the SSD market
• There have been about 800m SSDs shipped in 2018 - 2020
• 8% of 800 million is 64 million
• 10million of 64 million is ~15%

So Intel does about 15% of their volume as QLC SSDs. QLC drives are generally higher capacity than non-QLC so it's possible they do a higher percent of bits sold as QLC than 15%.

But doing 15% of all SSDs in the timeframe where the technology was launched and tuned is pretty good. Expect that 15% to be back loaded such that 2021 can be 15 - 20% of SSDs sold as QLC.

The other vendors are behind in their QLC offering and are not as far in that ramp up but it's definitely happening.