Unpowered SSDs slowly lose data • Hacker News Board

Re: Unpowered SSDs slowly lose data

#11

Post by Someone » Mon, Nov 24, 2025, 10:51 PM UTC

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.

You can run an error-correcting code on top of the regular blocks of memory, storing, for example (really an example; I don’t know how large the ‘blocks’ that you can erase are in flash memory), 4096 bits in every 8192 bits of memory, and recovering those 4096 bits from each block of 8192 bits that you read in the disk driver. I think that would be better than a simple “map low levels to 0, high levels to 1” scheme.

Re: Unpowered SSDs slowly lose data

#12

Post by formerly_proven » Mon, Nov 24, 2025, 10:53 PM UTC

Izkata wrote: post #10

brian-armstrong wrote: post #6

Powering the SSD on isn't enough. You need to read every bit occasionally in order to recharge the cell. If you have them in a NAS, then using a monthly full volume check is probably sufficient.

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.

Re: Unpowered SSDs slowly lose data

#13

Post by gosub100 » Mon, Nov 24, 2025, 10:54 PM UTC

paulkrush wrote: post #2

I had to search around and feel like a dork not knowing this. I have my data backed up, but I keep the SSDs because it's nice to have the OS running like it was... I guess I need to be cloning the drives to ISOs and storing on spinning rust.

or you could power them on 1-2x /year.

Re: Unpowered SSDs slowly lose data

#14

Post by brian-armstrong » Mon, Nov 24, 2025, 10:54 PM UTC

Izkata wrote: post #10

brian-armstrong wrote: post #6

Powering the SSD on isn't enough. You need to read every bit occasionally in order to recharge the cell. If you have them in a NAS, then using a monthly full volume check is probably sufficient.

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.

It's quite possible. Some SSDs are worse offenders for this than others. I have some Samsung 870 EVOs that lost data the way you described. Samsung knew about the issue and quietly swept it under the rug with a firmware update, but once the data was lost, it was gone for good.

Re: Unpowered SSDs slowly lose data

#15

Post by traceroute66 » Mon, Nov 24, 2025, 10:56 PM UTC

I assume this blog is a re-hash of the JDEC retention standards[1].

The more interesting thing to note from those standards is that the required retention period differs between "Client" and "Enterprise" category.

Enterprise category only has power-off retention requirement of 3 months.

Client category has power-off retention requirement of 1 year.

Of course there are two sides to every story...

Enterprise category standard has a power-on active use of 24 hours/day, but Client category only intended for 8 hours/day.

As with many things in tech.... its up to the user to pick which side they compromise on.

[1]https://files.futurememorystorage.com/proceedings/2011/20110...

Re: Unpowered SSDs slowly lose data

#16

Post by derkades » Mon, Nov 24, 2025, 10:58 PM UTC

brian-armstrong wrote: post #6

Powering the SSD on isn't enough. You need to read every bit occasionally in order to recharge the cell. If you have them in a NAS, then using a monthly full volume check is probably sufficient.

Isn't that the SSD controller's job?

Re: Unpowered SSDs slowly lose data

#17

Post by Yokolos » Mon, Nov 24, 2025, 10:59 PM UTC

formerly_proven wrote: post #8

> Even the cheapest SSDs, say those with QLC NAND, can safely store data for about a year of being completely unpowered. More expensive TLC NAND can retain data for up to 3 years, while MLC and SLC NAND are good for 5 years and 10 years of unpowered storage, respectively. This is somewhat confused writing. Consumer SSDs usually do not have a data retention spec, even in this very detailed Micron datasheet you won't f…

Any given TBW/DWPD values are irrelevant for unpowered data retention. Afaik, nobody gives these values in their datasheet and I'm wondering where their numbers are from, because I've never seen anything official. At this point I'd need to be convinced that the manufacturers even know themselves internally, because it's never been mentioned by them and it seems to be outside the intended use cases for SSDs

Re: Unpowered SSDs slowly lose data

#18

Post by bobmcnamara » Mon, Nov 24, 2025, 11:02 PM UTC

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.

Loads of drives do this(or SLC) internally. Though it would be handy if a physical format could change the provisioning at the kernel accessible layer.

Re: Unpowered SSDs slowly lose data

#19

Post by loloquwowndueo » Mon, Nov 24, 2025, 11:03 PM UTC

bossyTeacher wrote: post #9

This is why I would rather pay someone a couple of dollars per year to handle all this for me. If need be pay two providers to have a backup.

Who do you pay for this? (To rephrase : which cloud storage vendors do you use?) interested in the $2/month price point :)

Re: Unpowered SSDs slowly lose data

#20

Post by brian-armstrong » Mon, Nov 24, 2025, 11:03 PM UTC

derkades wrote: post #16

brian-armstrong wrote: post #6

Powering the SSD on isn't enough. You need to read every bit occasionally in order to recharge the cell. If you have them in a NAS, then using a monthly full volume check is probably sufficient.

Isn't that the SSD controller's job?

It would surely depend on the SSD and the firmware it's running. I don't think you can entirely count on it. Even if it were working perfectly, and your strategy was to power the SSD on periodicially to refresh the cells, how would you know when it had finished?