Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Unpowered SSDs slowly lose data

xda-developers.com

Post reply on HN
Print view View original

41–50 of 341 posts

Re: Unpowered SSDs slowly lose data

#41

Post by tcfhgj »

testartr wrote: post #26
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…

the market demands mostly higher capacity tlc/qlc works just fine, it's really difficult to consume the erase cycles unless you really are writing 24/7 to the disk at hundred of megabytes a second

I have a MLC SSD with TBW/GB much higher than the specified TBW/GB guarantee of usual qlc SSDs

Re: Unpowered SSDs slowly lose data

#43

Post by ethin »

brian-armstrong wrote: post #14
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.

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.

I ran into this firmware bug with the two drives in my computer. They randomly failed after a while -- and by "a while" I mean less than a year of usage. Took two replacements before I finally realized that I should check for an fw update

Re: Unpowered SSDs slowly lose data

#44

Post by [deleted] »

tcfhgj wrote: post #35
traceroute66 wrote: post #15

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 s…

With 1 year power-off retention you still loose data, so still a compromise on data retention

[deleted]

Re: Unpowered SSDs slowly lose data

#45

Post by antisthenes »

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 would run something like CHKDSK, or write a script to calculate a hash of every file on disk.

No idea if that's enough, but it seems like a reasonable place to start.

Re: Unpowered SSDs slowly lose data

#46

Post by dale_glass »

So on the off-chance that there's a firmware engineer in here, how does this actually work?

Like does a SSD do some sort of refresh on power-on, or every N hours, or you have to access the specific block, or...? What if you interrupt the process, eg, having a NVMe in an external case that you just plug once a month for a few minutes to just use it as a huge flash drive, is that a problem?

What about the unused space, is a 4 TB drive used to transport 1 GB of stuff going to suffer anything from the unused space decaying?

It's all very unclear about what all of this means in practice and how's an user supposed to manage it.

Re: Unpowered SSDs slowly lose data

#47

Post by tzs »

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 f -print0 | xargs -0 cat > /dev/null" to make sure every file gets read occasionally?

Re: Unpowered SSDs slowly lose data

#48

Post by 55873445216111 »

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…

All the big 3D NAND makers have already switched from floating gate to charge trapping. Basically the same as what you describe but basically the electrons get stuck in a non-conductive region instead of on an insulated gate.

Re: Unpowered SSDs slowly lose data

#49

Post by gruez »

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.

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.

Re: Unpowered SSDs slowly lose data

#50

Post by zozbot234 »

BaardFigur wrote: post #39

I don't use my drive much. I still boot it up snd write some data, just not the long term one. Am I in risk?

AIUI, informal tests have demonstrated quite a bit of data corruption in Flash drives that are literally so worn out that they might as well be about to fail altogether - well beyond any manufacturer's actual TBW specs - but not otherwise, least of all in new drives that are only written once over for the test. It seems that if you don't wear out your drive all that much you'll have far less to worry about.
Post reply on HN