Toshiba last week announced its first 3D NAND flash memory chips featuring QLC (quadruple level cell) BiCS architecture. The new components feature 64 layers and developers of SSDs and SSD controller have already received samples of the devices, which Toshiba plans to use for various types of storage solutions.

Toshiba’s first 3D QLC NAND chips feature 768 Gb (96 GB) capacity and uses 64 layers, just like the company’s BICS3 chips with 256 Gb and 512 Gb capacities launched in 2016 and 2017. Toshiba does not share further details about its 3D QLC NAND IC (integrated circuit), such as page size, the number of planes as well as interface data transfer rate, but expect the latter to be high enough to build competitive SSDs in late 2018 to early 2019 (that’s our assumption). Speaking of applications that Toshiba expects to use its 3D QLC NAND ICs, the maker of flash memory mentions enterprise and consumer SSDs, tablets and memory cards.

Endurance++

Besides intention to produce 768 Gb 3D QLC NAND flash for the aforementioned devices, the most interesting part of Toshiba’s announcement is endurance specification for the upcoming components. According to the company, its 3D QLC NAND is targeted for ~1000 program/erase cycles, which is close to TLC NAND flash. This is considerably higher than the amount of P/E cycles (100 – 150) expected for QLC by the industry over the years. At first thought, it comes across a typo - didn't they mean 100?. But the email we received was quite clear:

- What’s the number of P/E cycles supported by Toshiba’s QLC NAND?
- QLC P/E is targeted for 1K cycles.

It is unclear how Toshiba managed to increase the endurance of its 3D QLC NAND by an order of magnitude versus initially predicted. What we do know is that signal processing is more challenging with QLC than it is with TLC, as each cell needs to accurately determine sixteen different voltage profiles (up from 2 in SLC, 4 in MLC, and 8 in TLC). 

The easiest way to handle this would be to increase the cell size: by having more electrons per logic level, it is easier to maintain the data and also read from it / write to it. However, the industry is also in a density race, where bits per mm^2 is an issue. Also, to deal with read errors from QLC memory, controllers with very advanced ECC capabilities have to be used for QLC-based SSDs. Toshiba has its own QSBC (Quadruple Swing-By Codes) error correction technique, which it claims to be superior to LDPC (low-density parity-check) that is widely used today for TLC-powered drives. However, there are many LDPC implementations and it is unknown which of them Toshiba used for comparison against its QSBC. Moreover, there are more ECC methods that are often discussed at various industrial events (such as FMS), so Toshiba could be using any or none of them. The only thing that the company tells about its ECC now is that it is stronger than 120 bits/1 KB used today for TLC. In any case, if Toshiba’s statement about 1000 P/E cycles for QLC is correct, it means that that the company knows how to solve both endurance and signal processing challenges.

The main advantage of QLC NAND is increased storage density when compared to TLC and MLC, assuming the same die size. As was perhaps expected, die size numbers were not provided. However, last year Toshiba and Facebook talked about a case study QLC-powered SSD with 100 TB of capacity for WORM (write once read many) applications and it looks like large-capacity custom drives and memory cards will be the first to use QLC for cold storage. P/E cycles and re-write endurance isn't a concern for WORM at this stage.

Toshiba has begun to sample its 3D QLC NAND memory devices earlier this month to various parties to enable development of SSDs and SSD controllers. Taking into account development and qualification time, Toshiba plans to mass produce its BiCS3 768 Gb 3D QLC NAND chips around the same time it starts to make its the next generation BiCS4 ICs. The latter is set to hit mass production in 2018, but the exact timeframe is yet to be determined.

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Source: Toshiba

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  • Bullwinkle J Moose - Tuesday, July 04, 2017 - link

    Planned obsolescence ???

    ..."TOSHIBA that is!..."

    Endurance claims appear higher than normal and consumer availability is conveniently after the Company will be sold to the highest bidder

    Anyone sampling these now should torture the crap out of them to see if the endurance claims are anywhere near accurate before this Company Vaporizes as fast as its claims
    Reply
  • Alexvrb - Tuesday, July 04, 2017 - link

    I'm all for QLC... for secondary storage only. Basically replacing a storage HDD used for media with a QLC SSD. Current TLC drives are far too expensive to replace multi-TB HDDs. Anyway, in that scenario QLC would be good enough, you're not going to be hammering the drive with writes.

    For primary storage, a really good TLC based drive is a bare minimum. QLC, even supposed high endurance QLC, isn't good enough. Even if the endurance is truly as good as they claim, performance won't be. Especially when discussing PCIe-linked NVMe solutions (mostly M.2).

    I envision a rig with an PCIe 4.0/5.0 main drive (possibly PCM/ReRAM), and a high-density QLC drive for mass storage.
    Reply
  • mkozakewich - Wednesday, July 05, 2017 - link

    Keep in mind, four bits is only 33% more than three bits. They immediately jumped to the idea of 100TB drives, but it looks like their upcoming QLC chips would support about 4TB. (Or 8 TB, maybe.) Reply
  • Alexvrb - Wednesday, July 05, 2017 - link

    I have a 3TB HDD for secondary storage. A 4TB would be plenty. :D Pricing, of course, is key. I don't anticipate being able to go all-solid-state for at least a couple of years. Reply
  • Lolimaster - Wednesday, July 05, 2017 - link

    For media you don't SSD at all, HDD's are plenty fast and responsive for it. Another thing is having a huge collection of images where you want to use the thumbnails often. Reply
  • beginner99 - Wednesday, July 05, 2017 - link

    And the race to bottom just reached a new low. Won't be far till be reach JMicron level of bad. Reply
  • nandnandnand - Wednesday, July 05, 2017 - link

    This article has some serious grammar problems. Maybe 4 mistakes in the first two paragraphs. Reply
  • Gasaraki88 - Wednesday, July 05, 2017 - link

    I'm not trusting QLC with my data. Some TLC are bad enough. Maybe for WORM storage but no way for daily use. They can lie about the 1000 P/E cycles all they want. Reply
  • BurntMyBacon - Wednesday, July 05, 2017 - link

    3D-QLC getting 1000 P/E cycles is not as improbable as it seems. Samsung's move to 3D-NAND brought an odd situation where the MLC based 840PRO had less endurance than the TLC based 850EVO. Intel / Micron didn't get this benefit as they chose to use floating gates instead of charge traps in their architecture. Samsung, SK Hynix, and Toshiba all use charge trap. If I recall correctly, the 1000 P/E cycles metric is where planer NAND ended up. It is conceivable that Toshiba was able to make a 3D-QLC NAND with equal endurance to its planer TLC predecessor similar to how Samsung achieved a 3D-TLC with greater endurance than its planer MLC predecessor.

    However, I don't recall ever hearing 1000 P/E cycles used to describe the endurance of a 3D-TLC (charge-trap) NAND chip. An appropriate comparison point would be Toshiba's 3D-TLC vs Toshiba's 3D-QLC. That would help us to understand the true trade-offs made when moving to QLC.
    Reply
  • Glaring_Mistake - Wednesday, July 05, 2017 - link

    I can see that 3D QLC NAND could get to 1000 P/E cycles but that the 850 EVO has a higher endurance than the 840 Pro is just not accurate - the 850 EVO is rated at 2000 P/E and the 840 Pro at 3000 P/E.

    850 EVO may have a higher TBW but that is not the same as endurance.
    Nor are they likely to have established TBW in the same way since the 840 Pro had a TBW of 72TB if it was used as an enterprise-class drive.

    Endurance for planar TLC NAND varies quite a bit too, for example the Kingston UV400 is rated at 400-500 P/E while the Plextor M7V is rated at 2000 P/E, despite using the same NAND and controller!
    So it is not like 1000 P/E is set in stone for planar TLC NAND.

    Finally the 960 EVO was found by Nordichardware to be rated at around 1200 P/E despite using 3D TLC NAND with a Charge Trap.
    Reply

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