Tuesday, August 27th 2019

Toshiba Talks About 5-Bit-per-Cell (PLC) Flash Memory

Toshiba at the Flash Memory Summit announced they've managed to develop a 5-Bit-per-Cell memory solution Based on its BiCS 4 flash memory technologies, the feat was achieved using a modified module of Quad-Level Cell (QLC) memory. This shows the technology is not only feasible, but has room for improvement, since an adapted QLC technology will always be inferior to a natively-developed, Penta-Level Cell (PLC) solution.

To achieve this ability to store one extra bit of information per cell (compared to QLC), a new level of voltage refinement is required: the cell has to be able to change its state according to one of 32 voltage states, which, in turn, have to be read out correctly by the flash memory controller. This reduces the cell's performance and endurance (as does any increase in the number of bits per cell), and will require a number of solutions to mitigate and compensate for this reduced performance. However, density has become an increasing concern from manufacturers, hence the continued development of deeper, more variable voltage states that allow for even more information to be stored in the same silicon area. Higher density means cheaper solutions, but density increased in such a way has known trade-offs that have been much talked about ever since the transition from Single-Level Cell (SLC) up to the (nowadays ubiquitous) QLC.
Source: Tom's Hardware
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15 Comments on Toshiba Talks About 5-Bit-per-Cell (PLC) Flash Memory

#1
Crackong
This will be like 10Mb/s without cache.
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#2
Zareek
Crackong, post: 4105230, member: 185495"
This will be like 10Mb/s without cache.
Don't forget, good for only a dozen P/E cycles too. Semi-disposable thumb drives anyone???
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#4
bonehead123
londiste, post: 4105249, member: 169790"
Return of the WORM? :)
more like the slug :)
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#5
danbert2000
Honestly QLC is almost a bridge too far since it degrades to HDD performance levels when you saturate the cache. We're now going to see sub-HDD performance past the cache. I hope that MLC drives continue to be made, because that's just not going to cut it. I suppose if this allows 4 TB SSDs to reach $200 I would be interested for a game drive since writes aren't very important past the install process. Still, is anyone else wary of how reliable these drives are going to be? If the voltage changes by 4% you're in a different value now. I can't imagine how that's going to fly when an SSD is losing charge constantly when unpowered.
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#6
yakk
My guess would be SLC will be moved to almost exclusively for enterprise solutions.

TLC (with cache) will go to the premium consumer category, QLC $ cacheless TLC to mainstream, PLC budget.

It will allow manufacturers to increase their profits again.
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#7
Vayra86
danbert2000, post: 4105392, member: 165365"
Honestly QLC is almost a bridge too far since it degrades to HDD performance levels when you saturate the cache. We're now going to see sub-HDD performance past the cache. I hope that MLC drives continue to be made, because that's just not going to cut it. I suppose if this allows 4 TB SSDs to reach $200 I would be interested for a game drive since writes aren't very important past the install process. Still, is anyone else wary of how reliable these drives are going to be? If the voltage changes by 4% you're in a different value now. I can't imagine how that's going to fly when an SSD is losing charge constantly when unpowered.
I'm already staying away from QLC drives to be fair with you... Its just not worth it, at least with the current price/GB gap.

yakk, post: 4105419, member: 158293"
My guess would be SLC will be moved to almost exclusively for enterprise solutions.

TLC (with cache) will go to the premium consumer category, QLC $ cacheless TLC to mainstream, PLC budget.

It will allow manufacturers to increase their profits again.
And yet, if they cannot continually bring price/GB down on the whole stack over time, they won't be selling as much. The trend will continue, and QLC/PLC do provide breathing room on the market; the more volume they sell of that, the less scarce the better NAND will be. So in a way its good for everyone. We can't deny the demand is going to continue to go up.
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#8
yakk
Vayra86, post: 4105431, member: 152404"
And yet, if they cannot continually bring price/GB down on the whole stack over time, they won't be selling as much. The trend will continue, and QLC/PLC do provide breathing room on the market; the more volume they sell of that, the less scarce the better NAND will be. So in a way its good for everyone. We can't deny the demand is going to continue to go up.
Agree more options is better, just keep in mind this is price going down by offering lesser value. This is not older tech prices decreasing when replaced by better tech. We have the best tech so far with SLC, and creating worst tech options instead of better. The $/GB metric also aggregates different types of nand. Not aggregating this information would probably be more useful, as in:

SLC: $/GB
TLC w./ cache: $/GB
TLC cacheless: $/GB
QLC (slower cacheless version incoming later?): $/GB
PLC (slower cacheless version incoming later?): $/GB
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#9
Wavetrex
This is too much.
QLC is already pushing it... but PLC ? Come'on ...

And when you do the math, it's only 25% more bits for same number of cells ( QLC is 33% more than TLC, and TLC 50% more than M(2)LC )
Diminishing returns ... for massive loss in endurance.
Totally not worth it.
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#10
R-T-B
Do you want HDDs to appear reliable relative to flash Toshiba? Keep this up, and they might gain a marketing point.
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#11
Khonjel
Jesus FerdiNAND Christ!!! All the advancement of performance in almost every sector every year while SSD tech goes more backward.
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#12
yotano211
Crackong, post: 4105230, member: 185495"
This will be like 10Mb/s without cache.
I just saw a video where the host compared the samsung 1tb 860 and 860 qvo, both where 2.5in SSDs. After the cache was filled on the qvo it dropped down to 70mb/s write speed. I rather get a big storage HD for those speeds.
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#13
fynxer
This is very good, we need this PLC for low end drives like SATA and cheap usb memory, in the long run it will increase competition and give high end drives more capacity for less.
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#14
newtekie1
Semi-Retired Folder
yotano211, post: 4105758, member: 103073"
I just saw a video where the host compared the samsung 1tb 860 and 860 qvo, both where 2.5in SSDs. After the cache was filled on the qvo it dropped down to 70mb/s write speed. I rather get a big storage HD for those speeds.
Yeah, but in normal use you are very unlikely to fill up that cache.
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#15
beautyless
PLC flash with some spinning HDD cache? :laugh:

It doesn't matter using QLC since any flash storages are still faster than HDD in reading.
Those some cache should be enough for normal writing.
It'll start to make you feel disappointed when you write data that larger than its cache.

But for PLC, I couldn't see a serious reason to go.
SSD that slower than HDD is useless. Like a pricey HDD.
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