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QLC NAND on the way

SSDs are more and more a challenge for high-capacity
HDDs as prices drop and high-density memory dies
are being produced. Western Digital and Toshiba have
produced a QLC chip with 96 layers. What dies that mean?

First of all it means that each cell can store 4 bit of Information in one cell, meaning the cell can have 16 different states

Second it means, each cell is stacked 96 times, that means 1536 different information states on the space where one SLC, with one layer would typically hold.

The typical scheme of a QLC cell

That being said, the space has been increased by the factor 768 by now.

Usually more layers and multiple states also mean faster cell wearoff as a trade for more space.

Western Digital and Toshiba however managed to allow the classic 1000 Write cycles for QLC cells which makes them as durable as traditional TLC SSDs.

So while TLC cells have also increased their wearoff level to 3000 writecycles, QLC allows to pack more memory onto one die by now.

In numbers that is 1.33 Tbit/die. When stacking 16 dies, this would allow a storage of 2.33 TByte per chip which would allow real big SSDs.

Most SSDs have at least 8 chip packages and 1-2 ICCs on their PCB which would max out at 18.67 TB.

Speedwise, the chips allow a read speed of about 1.8GB/s and a typical write speed of 1.1GB/s at a rate of 150.000 IOP/s. Quite impressive as typical DLC/TLC SSDs max out at roughly 90.000 IOP/s.

Allowing 1 chip to be spare space, it could mean that we’re not far away from 16TB SSDs in the low-price segment anymore. Although it already has 16TB SSDs on the market, these are at a pricetag of about 8000US$ and only considered for use in data centers. But these are also SLC and MLC-SSDs and thus enclosed in 3.5″ housings which makes them unusable in notebooks or the like. With QLC, 16TB-SSDs in a traditional 2.5″ housing will become more realistic as more chips with bigger capacity fit on one memory package.

But although the higher capacity is appealing, the price tag for sure won’t. It is expectable that SSDs with 8TB and more will still yank out your purse and inhale 1000’s of $$$.

And tbh… anyone in need of a 4TB SSD in his device yet? I guess probably not because even Games still don’t gobble up so much space that it would rectify an investment of roughly 1500 US$. Most people would rather go for an 8TB HDD to fork over som rather unnecessary data or data that is not used that often.

But anyway, let’s see how QLC SSDs would affect the common SSD market and if we can see the prices slide especially for the higher capacity range. However SLC-SSDs still are ridiculously expensive (400GB demand for a whopping 4000 US$!!!) and MLC/TLC-SSDs are still state-of-the-art and reaching really fast speeds of up to 3.8GB/s Read and 2.5GB/s Write speeds with about 500.000 IOP/s.

So it’s rather uncommon that we will see low-priced MLC/TLC-SSDs in order to make room for the slower QLC disks.

From August 7 to 9, 2018, the Flash Memory Summit in Santa Clara, California will open it’s doors again for the media and we may expect some more news.


July 23, 2018 Netspark - 1588 posts - Member since: May 9th, 2011 No Comments »

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