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Unpowered SSDs slowly lose data

xda-developers.com

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Re: Unpowered SSDs slowly lose data

#71

Post by userbinator »

sevensor wrote: post #3

Flash is programmed by increasing the probability that electrons will tunnel onto the floating gate and erased by increasing the probability they will tunnel back off. Those probabilities are never zero. Multiply that by time and the number of cells, and the probability you don’t end up with bit errors gets quite low. The difference between slc and mlc is just that mlc has four different program voltages instead of t…

I do wonder why there’s no way to operate qlc as if it were mlc, other than the manufacturer not wanting to allow it.

There is a way to turn QLC into SLC: https://news.ycombinator.com/item?id=40405578

Re: Unpowered SSDs slowly lose data

#72

Post by Izkata »

gruez wrote: post #49
Izkata wrote: post #10

Earlier quoted context omitted.

Huh. I wonder if this is why I'd sometimes get random corruption on my laptop's SSD. I'd reboot after a while and fsck would find issues in random files I haven't touched in a long time.

If you're getting random corruption like that, you should replace the SSD. SSDs (and also hard drives) already have built-in ECC, so if you're getting errors on top, it not just random cosmic rays. It's your SSD being extra broken, and doesn't bode too well for the health of the SSD as a whole.

I bought a replacement but never bothered swapping it. The weird thing is the random corruption stopped happening a few years ago (confirmed against old backups, so it's not like I'm just not noticing).

Re: Unpowered SSDs slowly lose data

#74

Post by nixpulvis »

testartr wrote: post #25

what is the exact protocol to "recharge" an ssd which was offline for months? do I just plug it in and let the computer on for a few minutes? does it needs to stay on for hours? do I need to run a special command or TRIM it?

I too wonder about this. I'd love to see someone build a simulated "fast decay" SSD which can show how various firmware actually behaves.

Re: Unpowered SSDs slowly lose data

#75

Post by Izkata »

formerly_proven wrote: post #12
Izkata wrote: post #10

Earlier quoted context omitted.

Huh. I wonder if this is why I'd sometimes get random corruption on my laptop's SSD. I'd reboot after a while and fsck would find issues in random files I haven't touched in a long time.

Unless your setup is a very odd Linux box, fsck will never check the consistency of file contents.

It found problems in the tree - lost files, wrong node counts, other stuff - which led to me finding files that didn't match previous backups (and when opened were obviously corrupted, like the bottom half of an image being just noise). Once I found this was a problem I've also caught ones that couldn't be read (IOError) that fsck would delete on the next run.

I may not have noticed had fsck not alerted me something was wrong.

Re: Unpowered SSDs slowly lose data

#76

Post by dboreham »

Quick note to not store any valuable data on a single drive. And when you store it on two drives, don't use the same kind of drive. (Speaking from bitter experience using spinning drives in servers that had a firmware bug where they all died at the time number of seconds of power-on time).

Re: Unpowered SSDs slowly lose data

#77

Post by userbinator »

One key point about retention which is not often mentioned, and indeed neither does this article, is that retention is inversely proportional to program/erase cycles and decreases exponentially with increasing temperature. Hence why retention specs are usually X amount of time after Y cycles at Z temperature. Even a QLC SSD that has only been written to once, and kept in a freezer at -40, may hold data for several decades.

Manufacturers have been playing this game with DWPD/TBW numbers too --- by reducing the retention spec, they can advertise a drive as having a higher endurance with the exact same flash. But if you compare the numbers over the years, it's clear that NAND flash has gotten significantly worse; the only thing that has gone up, multiplicatively, is capacity, while endurance and rentention have both gone down by a few orders of magnitude.

For a long time, 10 years after 100K cycles was the gold standard of SLC flash.

Now we are down to several months after less than 1K cycles for QLC.

Re: Unpowered SSDs slowly lose data

#78

Post by dboreham »

JensenTorp wrote: post #56
tzs wrote: post #47

What about powered SSDs that contain files that are rarely read? My desktop computer is generally powered except when there is a power failure, but among the million+ files on its SSD there are certainly some that I do not read or write for years. Does the SSD controller automatically look for used blocks that need to have their charge refreshed and do so, or do I need to periodically do something like "find / -type…

I also need an answer to this.

It's fine. But the whole drive can turn to dust at any time, of course.

Re: Unpowered SSDs slowly lose data

#79

Post by markhahn »

jcynix wrote: post #57

Hmm, so what about these modern high density hard drives which store track parameters for their servos in on-board flash (aka OptiNAND)? Do we get "spinning rust" which might loose the information where exactly it stored the data? https://blog.westerndigital.com/optinand-explained/

shouldn't really be a problem, since the capacity required for this use is so low.

the real issue here is QLC in which the flash cell's margins are being squeezed enthusiastically...

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