[HN Gopher] Unpowered SSDs slowly lose data
___________________________________________________________________
Unpowered SSDs slowly lose data
Author : amichail
Score : 43 points
Date : 2025-11-24 19:25 UTC (3 hours ago)
(HTM) web link (www.xda-developers.com)
(TXT) w3m dump (www.xda-developers.com)
| paulkrush wrote:
| 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.
| dpoloncsak wrote:
| I could be wrong, but I believe the general consensus is along
| the lines of "SSDs for in-use data, it's quicker and wants to
| be powered on often. HDDs for long-term storage, as they don't
| degrade when not in use nearly as fast as SSDs do.
| joezydeco wrote:
| I've been going through stack of external USB drives with
| laptop disks in them. They're all failing in some form or
| another. I'm going to have to migrate it all to a NAS with
| server-class drives I guess
| pluralmonad wrote:
| I learned this when both my old laptops would no longer boot
| after extended off power time (couple years). They were both
| stored in a working state and later both had SSDs that were
| totally dead.
| gosub100 wrote:
| or you could power them on 1-2x /year.
| sevensor wrote:
| 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 two, so reading back the
| data you have to distinguish between charge levels that are
| closer together. Same basic cell design. Honestly I can't quite
| believe mlc works at all, let alone qlc. 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.
| Someone wrote:
| > 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.
| brian-armstrong wrote:
| 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.
| Izkata wrote:
| 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.
| formerly_proven wrote:
| Unless your setup is a very odd Linux box, fsck will never
| check the consistency of file contents.
| brian-armstrong wrote:
| 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.
| formerly_proven wrote:
| > 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 find it:
| https://advdownload.advantech.com/productfile/PIS/96FD25-S2T...
| Meanwhile the data retention spec for enterprise SSDs is at the
| end of their rated life, which is usually a DPWD/TBW intensity
| you won't reach in actual use anyway - that's where numbers like
| "3 months @ 50 degC" or whatever come from.
|
| In practice, SSDs don't tend to loose data over realistic time
| frames. Don't hope for a "guaranteed by design" spec on that
| though, some pieces of silicon are more equal than others.
| bossyTeacher wrote:
| 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.
| traceroute66 wrote:
| 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..
| .
___________________________________________________________________
(page generated 2025-11-24 23:00 UTC)