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Comment by Robotbeat | Hacker News Reader

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.

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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?

It's essentially charging a cell to a level on write and measuring the voltage on read.

So technically it's up to firmware to decide, assuming the hardware have stuff (ADC/DAC etc.) to handle it would be possible.

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.

2.5" hard drives are usually very robust when powered down. That comes from the age when they were expected to be used in laptops.

I was about to say “the age? You mean today” and realized 2.5” “laptop” hard drives aren’t really used in laptops anymore, even the low-end ones. Damn.

Funny, I thought the exact same thing. I still think of SSD's as "fancy" like it's still 2008 or something.

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.

Yep, an unpowered hard disk will be rated to something like 250 g's of shock and -40C to +70C temperatures. You could put it in a sealed pyrex container with some silica desiccant and some foam padding. Just keep it from sliding around loose, and it should physically survive anything but direct impact in a collision.

I’m not sure either would be great… An untested backup is a backup that may as well never have happened, make sure to test your backups!

This is very much a backup option of last resort. I maintain a real backup solution inside my house, but basically nowhere to keep something off-site. I do not consider the cloud acceptable. For my top tier priority data (low total file size), I really want something stored elsewhere.

Given the non-ideal state of the car, I think the plan would be to just replace that drive on an annual basis.

It's still very valuable to have a reasonably robust backup even if you skimp on maintenance, though. No one's going to smash your hard disk with a hammer to punish you for being lazy. 90% isn't much different than 99% in an exceptional circumstance.

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?

Yes, it does precisely that.

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.

And yet there are still people who will post about the good old days and the evils of MLC, as if current SSDs were not demonstrably better in every way.

They aren't. Write endurance is significantly lower than SLC, it's just compensated for by lots of write leveling.

More precisely, endurance and retention become exponentially lower with each additional bit stored per cell, while capacity only increases multiplicatively.

They are better. SLC is improving as much as MLC. The ratio of speed, durability, and capacity is the same between SLC/MLC/TLC, but modern MLC is faster and more durable than 5-year-old SLC.

Exactly. And I do not care what the low-level bit performance is if the device-level performance is better.

>modern MLC is faster and more durable than 5-year-old SLC

great April fools joke

You are probably writing this from a computer using a TLC SSD. Outside of applications that need extreme latency, pure SLC has almost completely disappeared from the storage world. From materials science to management algorithms, a lot has advanced in flash technology in terms of durability.

It's true that TLC and MLC have for good reason displaced SLC. However, in no way are they even anywhere near the old SLC in durability. ~5 years old SLC literally had 100 times more write endurance (as in, how many times you can rewrite each bit, not total amount of writes in the drive) than typical modern TLC.

That is pretty much true, and it's pretty much the only stat that hasn't improved. However, write endurance isn't really a factor in terms of data durability. It has to do more with the drive's ability to continue being written than with the safety of data that has already been written. If your drive goes read-only or loses capacity, that has to do with write endurance. Neither of those involve data loss.

Citation needed

I still remember the bubble memory system that would someday replace HDD back in the 80s

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.

They do operate reliably in the same environment; what you're talking about is operating in ideal environments.

When we're talking ideals, it shouldn't come as a surprise that two fundamentally different things desire two fundamentally different ideal environments.

I appreciate your distinction, but I still think my point stands. As the technology is iterated on and refined based on years of feedback from real world use, I would expect the ideal environment for a given class of technology to converge on the typical operating environment. Decisions will be made that shift the physical properties one way or another. Silicon will be doped with different impurities. Transistors will be made with different sizes and geometries. Different metals and plastics will be used. Different voltages will be applied.

People desire practical technological solutions to serve their needs. A box of "spinning rust" doesn't desire much of anything. A CPU is just a rock that's better at arithmetic than another rock.

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).

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