Comment by Robotbeat
3 years ago
Interestingly, unpowered flash memory has much higher retention rates at low temperatures and much SHORTER retention rates at elevated temperatures (the typical JEDEC spec is just 1 year retention at 30C unpowered).
Flash memory in a freezer (assuming you don't have cold-induced circuit board failures due to CTE mismatch) could last hundreds of years. In a hot car, maybe a month. https://www.curtisswrightds.com/media-center/blog/extended-t...
None of that is particularly surprising, but what's interesting is that write endurance can have the opposite effect... Writing at high temperature (followed by cooling to ambient... or lower) actually improves data retention over just writing at ambient.
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.
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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.
Nuts! I have been thinking of leaving an emergency encrypted backup in my car, but evidently that is likely to self cook almost immediately. I assumed the lifetime was not great, but that is far more aggressive than I had feared.
Maybe use a 2.5" hard drive rather than an SSD? I can't think of any downsides for that purpose.
Assuming the car is actually used, an HDD would be subject to numerous physical stresses. Not exactly something HDDs like.
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I had some immediate disgust thinking, "Moving parts? I am done with those!", but I think you are totally right. The 2.5" hard drive is likely to have better endurance in the poor environment and repeated thermal cycling of a car trunk.
Great idea. Hopefully I never have to try and read data from it.
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There are plenty of places under your car where you can securely mount a box to hold the drive, if you really want to do this, but there are probably better places to keep a backup than a moving vehicle.
No argument that these it is not an ideal storage environment, but it costs little to setup. I do not want to rely upon the cloud, and I have limited access to off-site locations.
Given unfortunate circumstances, I might lose the home one day (fire, burglary) or the car, but unlikely to be both.
You can get industrial SLC, it's just expensive and small. Pick your 8 most previous GB...
Would it cook in the trumk (assuming your car has one)
In a warm climate the trunk is likely no better..
I don't understand this. Most laptops will have internal / ssd temperatures over 50C, and yet data usually lasts for years?
>>"client class SSD must maintain its data integrity at the defined BER for only 500 hours at 52°C (less than 21 days) or 96 hours at 66°C (only four days)."
Those are powered on when the laptop is on.
Right, but through which mechanism does that maKe a difference? Does controller periodically rewrite all contents? In other words how, does being powered-on increase retention of static data?
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Also all of these are minimum requirements. They don't actually imply much, except about the state of technology when the statement was written. Flash has been improving very quickly on all axes.
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I cool my server to 30°-35° HDD temperatures, because that's supposed to increase their life. However, all my SSDs are then at 23-27° [1]. I think I saw some long endurance tests and they pointed out that failure rates for SSDs increase slightly below 25°. Tricky tradeoff.
[1]: https://i.ibb.co/dtt6dwj/ssd-hdd-tmp.png
HDDs and SSDs operate on fundamentally different technologies, so it shouldn't be a surprise that they desire vastly different environments to reside in.
I would think that over many years of iteration by engineers, both would converge on functioning reliably in the same environment. They're both intended to be integrated into computer systems after all.
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Yeah, it's interesting because I think some parts of the SSD want cooler temperatures but writing to the flash might actually do less damage to the cells if you're writing at higher temperatures (higher charge mobility in silicon).