News New X-NAND Tech Detailed: SLC Speed at QLC Density and Cost

hotaru251

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Oct 30, 2014
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this is very good news.
If it does in fact come out at QLC prices...HDD's will be dead for anythign other than archiving (where they need MASSIVE TB's)

can't wait for it to come to market and try it out in RAID:geek:
 
Just hope the life of it is also the equivalent to SLC flash .
The write endurance of QLC is generally not a problem at higher capacities, at least for typical desktop usage scenarios where you are not writing hundreds of gigabytes to the drive every single day. With more capacity comes more cells to perform wear leveling across, so for capacities of around 1TB or more, QLC should have enough endurance to not be a real concern.
 

hannibal

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It did not happen unless it was tested by independent tester...
There has been Many promising new alternate to normal nand, but so far only Intel with Micron has come out with something like this... but at wery high cost...
so I hope for the best but am not holding my breath yet. Promising, but we need consumer products to make this real.
 

Maxxify

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It did not happen unless it was tested by independent tester...
There has been Many promising new alternate to normal nand, but so far only Intel with Micron has come out with something like this... but at wery high cost...
so I hope for the best but am not holding my breath yet. Promising, but we need consumer products to make this real.
I think one thing people confuse a lot with this technology is that they assume it's different NAND - it's explicitly not. It's meant to be a drop-in change to existing flash. What you're talking about is 3D Xpoint (crossbar memory) which is a completely different thing than NAND. Although, X-NAND is decidedly not oriented at consumer usage.

Getting more out of QLC using a variety of techniques is nothing new, in fact there were more than just this at FMS this year.
 

Giroro

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Jan 22, 2015
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Imagine how good the memory would be if they put this kind of effort into improving good NAND instead of trying to "save" trash bottom-of-the-barrel QLC.
QLC is never going to be good enough or cheap enough to be worth buying over TLC. Anything that improves QLC can be used to improve TLC by an even wider margin, so it's always going to be worth paying that extra ~$20 for the much higher speeds and 10x the endurance... And that's just TLC, which is still bad compared to MLC and especially SLC, but at least in that case the price drop was actually more significant.
 
Imagine how good the memory would be if they put this kind of effort into improving good NAND instead of trying to "save" trash bottom-of-the-barrel QLC.
QLC is never going to be good enough or cheap enough to be worth buying over TLC. Anything that improves QLC can be used to improve TLC by an even wider margin, so it's always going to be worth paying that extra ~$20 for the much higher speeds and 10x the endurance... And that's just TLC, which is still bad compared to MLC and especially SLC, but at least in that case the price drop was actually more significant.
I'm not sure if you actually read the article, but at least according to what they are claiming...

  1. X-NAND makes QLC perform more like SLC.
  2. X-NAND dramatically improves the endurance of QLC.
  3. X-NAND is most useful for QLC, since it supposedly fixes its main limitations.
So, pretty much the opposite of what you are suggesting. There might be some limitations, but it definitely seems like a positive development.

And as I pointed out before, QLC is already arguably pretty good when implemented properly. The vast majority of today's applications and usage scenarios won't see much benefit from higher-end flash, so it doesn't make much sense for most people to pay more for it. Maybe someday, applications will be optimized to fully make use of something like 3D Xpoint, and the pricing will be down to practical levels, but today those advanced storage technologies are terribly priced, and don't really improve the performance of most real-world tasks substantially. Even for the higher-end NAND drives, many people would be better served by getting a lower-end drive with double the capacity for about the same price than to pay a huge premium for a given capacity with maybe 10% better real-world performance. SSD pricing has certainly gotten better, but it's still high enough that many people are getting lower-capacity drives than would be ideal, so reducing costs is still an important focus.
 

2Be_or_Not2Be

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"The tech is aimed at embedded devices, AI, and the cloud, including NAS, data center, and edge computing. "

To those mentioning consumer usage, I got the impression this was intended for datacenter/enterprise implementation before it might be incorporated into consumer applications. Only "embedded devices" were mentioned in the usage cases. So I think they intend to get their money from enterprise, either through direct purchases/licensing deals. Sounds like a good target for revenue. If it delivers exactly what they said, then it will be a great tech to have & could have some significant savings for enterprise storage as well.
 

Maxxify

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FMS as a whole is geared towards enterprise, the data center, AI/5G, etc. That's not to say X-NAND can't or won't have consumer applications. However, having QLC utilized in this manner for SLC performance is probably not a priority in the consumer space as daily workloads aren't that demanding. The more traditional SLC caching + QLC, as he covers in the presentation, is quite sufficient. However, it and other technologies at FMS do at least show a trend towards making QLC mainstream.
 

Maxxify

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  1. X-NAND makes QLC perform more like SLC.
  2. X-NAND dramatically improves the endurance of QLC.
It always writes first in SLC mode, and further always at SLC speeds. There's three banks with the first writing incoming data to SLC, a second bank where SLC data is moved to QLC, and a third bank where SLC is erased to make room for more writes. The reason this works so well is because SLC mode tends to have a tPROG (write latency) of ~200µs - this applies to NAND in consumer drives as well, by the way - while QLC in his example is at a total of 6400µs (this is not precise, as newer consumer QLC can manage 1/2 to 1/3 this latency, but he's talking for all pages). Therefore you can write 32 SLC pages (e.g. 32x200µs = 6400µs) while keeping pace with data moving to QLC, therefore avoiding the SLC cache drop-off you usually see. This makes QLC uniquely qualified for this technology but that's also true of other characteristics - namely, if you're splitting 16KB pages into 4KB I/O chunks/subpages (16 / 4) and then the page buffer into 1KB chunks per plane (4 / 4), 4-bit QLC with 1-bit SLC is a match made in heaven.

As for endurance, typically on a consumer drive you'll have static, dynamic, or a hybrid SLC caching scheme. Dynamic SLC shares a wear zone with native flash, you're converting back-and-forth, you can even increase write amplification with it. Static SLC, however, is dedicated and has its own wear zone, usually in the 30K-40K P/E range (vs. 100K with native SLC or 1.6K with dynamic SLC + QLC). If all the writes are done to this sort of static SLC, depending on workload you can increase overall endurance significantly for a variety of reasons. For example, writing/folding out from SLC is done sequentially and not randomly which reduces write amplification. You can also defer writes or erases. I'm not privy to the exact workings of X-NAND in this capacity (I made a lot of assumptions) but I am in contact with the creator and will certainly be investigating this more. However, it basically offers SLC-like performance with respectable endurance.

There was a query about endurance during FMS, and this was his reply:

"No, the endurance will not be reduced. Because the SLC pages are not erased immediately. Although their data is re-programmed to QLC page immediately, the SLC pages’ erasure will be hold until all the SLC pages in the bank are programmed, then all the SLC pages of the bank will be erased together. Therefore, the endurance is the same as conventional SLC cache. "
 

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