Comment by userbinator
3 years ago
Is the 1-year spec after all the rated program/erase cycles have already been used, so the flash cells are worn and much "leakier"?
That's still rather disturbing, since I have datasheets for NAND flash from around 2 decades ago that specify 10 years retention after 100K cycles (although probably at 25C), and some slightly newer ones with 5 years / 1.5K cycles (MLC); and also explains the increasing secrecy surrounding the flash industry. The very few I could find for TLC don't even mention retention and endurance is vaguely specified, and refer you to some, probably super-secret, qualification report for the actual numbers.
Then again, perhaps I shouldn't be surprised ever since they came up with the misnomers that are "TLC" and now "QLC", and nearly drove SLC to extinction. I don't want 3x or 4x more storage for the same price (or 1/3 or 1/4 the price) if it's 1/8th or 1/16th exponentially more unreliable --- that's how the physics works and there's no way around that --- but that's what they seem to be pushing for.
You can get $13 128GB TLC SSDs as mentioned in the article but I don't see any $39 128GB SLC SSDs being made, nor $13 ~40GB SLC SSDs, despite the fact that such a device would have the exact same cost per NAND cell (and as a bonus, be much faster and simpler since SLC needs much less ECC and advanced wear leveling algorithms than TLC/QLC.)
Not just SLC (1bit per cell). One thing that exasperates me is that one can't find even MLC drives anymore (2bits per cell), now everything is TLC or QLC (QLC sounds as a bad joke, how are they able to sell that thing?).
A few years ago Samsung Pro SSDs were MLC disks, but suddenly they changed them to TLC. They are shameless for calling them 3bit-MLC that is pure oxymoron. 3bits per cell is TLC-mode, and the degradation is higher than a MLC-mode. Basically, it is a price increase by deceiving the consumer (to achieve this, they have reduced the characteristics of their other lines also. shameless).
The misnomer drives me nuts, it should be called 8LC or 16LC for the ever-finer states they have to resolve, and that would make the dismal endurance and reliability make sense.
> but I don't see any $39 128GB SLC SSDs being made, nor $13 ~40GB SLC SSDs
Shouldn’t it be 2^3 times more expensive than TLC? IOW a $104 128GB SLC SSD or a $13 16GB SLC SSD.
Edit: guess you’re right userbinator
NAND cell modes: SLC 1-bit per cell, MLC 2-bit, TLC 3-bit, QLC 4-bit.
And those cell modes are usually determined by the firmware/hardware controller of the NAND memory.
The more bits stored per cell, the greater is the degradation. SLC-mode requires in average 2.2 times more erase cycles than MLC to achieve the same error rate [1].
So the differences in prices make it look as if some manufacturers are playing with us...
[1] https://www.researchgate.net/publication/254005562_Software_...
PS: QLC-mode is the worst in all terms, the highest degradation and lower speed.
Does it mean that with "raw" flash it's possible to use it in either mode? I guess it should not be impossible to create DIY SSD?
1 reply →
No. Each cell in TLC stores three bits (and has 8 actual voltage levels, hence the misnomer), and thus TLC should either be a third of the cost of SLC at the same density, or three times the density as SLC for the same cost.