SSDs are on track to get bigger and cheaper thanks to PLC technology

guest · Sep 28, 2019

New Intel, Toshiba SSD technologies squeeze more bits into each cell
Storage of five bits in every NAND cell is coming, courtesy of Intel and Toshiba
September 28, 2019
https://arstechnica.com/gadgets/201...echnologies-squeeze-more-bits-into-each-cell/

Wednesday, Intel announced it's joining Toshiba in the PLC (Penta-Level Cell, meaning 5 bits stored per individual NAND cell) club. Intel has not yet commercialized the technology, so you can't go and buy a PLC SSD yet—but we can expect the technology will lead eventually to higher-capacity and cheaper solid state drives.

Unfortunately, while PLC SSDs will likely be bigger and cheaper, they'll probably also be slower.
We can't tell you exactly how fast PLC media will (or won't) be, but the progression we see here doesn't make it look great. As the number of distinct voltage levels per cell that must be reliably detected increases, the time it takes to accurately and reliably read or write to those cells increases along with it.

With sequential write speeds to QLC media already decreasing to or below that of conventional hard drives, PLC seems likely to be a niche player that will compete far more with NAS and datacenter drives than it does with laptop and desktop SSDs aimed at high performance.
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These are the industry terms for the various NAND storage levels:

SLC—Single Layer Cell. One bit stored per cell. Typically only found in small cache layers, or extremely high-performance enterprise SSDs.

MLC—Multi Layer Cell. In the real world, this refers specifically to two bits per cell. Examples include early consumer drives such as Intel X-25M and modern high-performance drives such as Samsung 860 Pro.

eMLC—enterprise Multi Layer Cell. This is, effectively, just MLC with write speeds throttled in order to reduce error rates. Still only two bits stored per cell.

TLC—Triple Layer Cell. Three bits stored per cell. Most modern consumer drives, such as Samsung 860 EVO and Western Digital Blue, are TLC drives.

QLC—Quadruple Layer Cell. Four bits stored per cell. Used by a few high-capacity, low-cost consumer SSDs such as Samsung's 860 QVO and Intel's 660P.

PLC—Penta Layer Cell, because an acronym for "quintuple" would have collided with 4-bit QLC. Five bits stored per cell. This is new technology that Intel and Toshiba have debuted this quarter.

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Rasheed187 · Sep 28, 2019

OK, in other words, they are uninteresting for use in desktops and laptops, what a bummer.

guest · Oct 7, 2019

PLC flash: A solid state candidate for analytics and archives?
October 7, 2019
https://www.computerweekly.com/news...id-state-candidate-for-analytics-and-archives

That could mean flash drives that start to push towards 20TB, and while they will be cheaper to run than equivalent-sized spinning disk media, they will be limited in terms of I/O performance, endurance and therefore use cases.

But every increase in cell state capacity has come with a cost in terms of durability. As each generation has packed more electrical operations into a smaller space, the longevity of cells has been eroded.
Manufacturers will try to mitigate these issues by over-provisioning capacity. Western Digital, for example, is working on “zoning”, where data of certain types is restricted to certain areas on the flash die, with the aim of making data as near to write-once-read-many as possible.

But the big question is: is PLC flash achievable as a product and what will its characteristics and limitations mean for possible use cases?
Well, QLC is mainly aimed at use cases that see little change in data stored on devices that use it, and PLC will follow suit.
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SSDs are on track to get bigger and cheaper thanks to PLC technology

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