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Unpowered SSDs slowly lose data

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Re: Unpowered SSDs slowly lose data

#51

Post by zozbot234 »

dale_glass wrote: post #46

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,…

Typically unused empty space is a good thing, as it will allow drives to run in MLC or SLC mode instead of their native QLC. (At least, this seems to be the obvious implication from performance testing, given the better performance of SLC/MLC compared to QLC.) And the data remanence of SLC/MLC can be expected to be significantly better than QLC.

Re: Unpowered SSDs slowly lose data

#52

Post by unsnap_biceps »

PaulKeeble wrote: post #36
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?

We really don't know. One thing I wish some of these sites would do is actually test how long it takes for the drives to decay and also do a retest after they have been left powered for say 10 minutes to an hour, read completely, written to a bit etc and see if they can determine what a likely requirement is. The problem is the test will take years, be out of date by the time its released and new controllers will be…

There was one guy who tested this

https://www.tomshardware.com/pc-components/storage/unpowered...

    The data on this SSD, which hadn't been used or powered up for two years, was 100% good on initial inspection. All the data hashes verified, but it was noted that the verification time took a smidgen longer than two years previously. HD Sentinel tests also showed good, consistent performance for a SATA SSD.
    Digging deeper, all isn't well, though. Firing up Crystal Disk Info, HTWingNut noted that this SSD had a Hardware ECC Recovered value of over 400. In other words, the disk's error correction had to step in to fix hundreds of data-based parity bits.
    ...
    As the worn SSD's data was being verified, there were already signs of performance degradation. The hashing audit eventually revealed that four files were corrupt (hash not matching). Looking at the elapsed time, it was observed that this operation astonishingly took over 4x longer, up from 10 minutes and 3 seconds to 42 minutes and 43 seconds.
    Further investigations in HD Sentinel showed that three out of 10,000 sectors were bad and performance was 'spiky.' Returning to Crystal Disk Info, things look even worse. HTWingNut notes that the uncorrectable sectors count went from 0 to 12 on this drive, and the hardware ECC recovered value went from 11,745 before to 201,273 after tests on the day.

Re: Unpowered SSDs slowly lose data

#53

Post by gruez »

zozbot234 wrote: post #51
dale_glass wrote: post #46

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,…

Typically unused empty space is a good thing, as it will allow drives to run in MLC or SLC mode instead of their native QLC. (At least, this seems to be the obvious implication from performance testing, given the better performance of SLC/MLC compared to QLC.) And the data remanence of SLC/MLC can be expected to be significantly better than QLC.

>as it will allow drives to run in MLC or SLC mode instead of their native QLC

That depends on the SSD controller implementation, specifically whether it proactively moves stuff from the SLC cache to the TLC/QLC area. I expect most controllers to do this, given that if they don't, the drive will quickly lose performance as it fills up. There's basically no reason not proactively move stuff over.

Re: Unpowered SSDs slowly lose data

#54

Post by fairfeather »

dale_glass wrote: post #46

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,…

SSD firmware engineer here. I work on enterprise stuff, so ymmv on consumer grade internals.

Generally, the data refresh will all happen in the background when the system is powered (depending on the power state). Performance is probably throttled during those operations, so you just see a slightly slower copy while this is happening behind the scenes.

The unused space decaying is probably not an issue, since the internal filesystem data is typically stored on a more robust area of media (an SLC location) which is less susceptible to data loss over time.

As far as how a user is supposed to manage it, maybe do an fsck every month or something? Using an SSD like that is probably ok most of the time, but might not be super great as a cold storage backup.

Re: Unpowered SSDs slowly lose data

#55

Post by zozbot234 »

unsnap_biceps wrote: post #52
PaulKeeble wrote: post #36

Earlier quoted context omitted.

We really don't know. One thing I wish some of these sites would do is actually test how long it takes for the drives to decay and also do a retest after they have been left powered for say 10 minutes to an hour, read completely, written to a bit etc and see if they can determine what a likely requirement is. The problem is the test will take years, be out of date by the time its released and new controllers will be…

There was one guy who tested this https://www.tomshardware.com/pc-components/storage/unpowered... The data on this SSD, which hadn't been used or powered up for two years, was 100% good on initial inspection. All the data hashes verified, but it was noted that the verification time took a smidgen longer than two years previously. HD Sentinel tests also showed good, consistent performance for a SATA SSD. Digging deepe…

Note that the SSD that showed corrupted files was the one that had been worn out well beyond the manufacturer's max TBW rating (4× the TBW or so). There was a difference of two-to-three orders of magnitude in the ECC count between the "fresh" and the worn-out SSD; I'd call that very significant. It will be interesting to see if there's any update for late 2025.

Re: Unpowered SSDs slowly lose data

#56

Post by JensenTorp »

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.

Re: Unpowered SSDs slowly lose data

#58

Post by gruez »

fairfeather wrote: post #54
dale_glass wrote: post #46

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,…

SSD firmware engineer here. I work on enterprise stuff, so ymmv on consumer grade internals. Generally, the data refresh will all happen in the background when the system is powered (depending on the power state). Performance is probably throttled during those operations, so you just see a slightly slower copy while this is happening behind the scenes. The unused space decaying is probably not an issue, since the int…

>Generally, the data refresh will all happen in the background when the system is powered (depending on the power state).

How does the SSD know when to run the refresh job? AFAIK SSDs don't have an internal clock so it can't tell how long it's been powered off. Moreover does doing a read generate some sort of telemetry to the controller indicating how strong/weak the signal is, thereby informing whether it should refresh? Or does it blindly refresh on some sort of timer?

Re: Unpowered SSDs slowly lose data

#59

Post by binaryturtle »

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/

I wonder too. I don't trust SSDs/ flash for my archives, hence I'm stuck on max. 18TB drives atm.

Re: Unpowered SSDs slowly lose data

#60

Post by seg_lol »

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…

You should absolutely be doing a full block read of your disk, dd if=/dev/disk of=/dev/null every couple weeks
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