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Unpowered SSDs slowly lose data

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Re: Unpowered SSDs slowly lose data

#151

Post by dachris »

pbmonster wrote: post #133
hxorr wrote: post #92

Earlier quoted context omitted.

I also seem to remember reading retention is proportional to temperature at time of write. Ie, best case scenario = write data when drive is hot, and store in freezer. Would be happy if someone can confirm or deny this.

I know we're talking theoretical optimums here, but: don't put your SSDs in the freezer. Water ingress because of condensation will kill your data much quicker than NAND bit rot at room temperature.

Would an airtight container and liberal addition of dessicants help?

Re: Unpowered SSDs slowly lose data

#152

Post by geokon »

gblargg wrote: post #136
easygenes wrote: post #62

Earlier quoted context omitted.

So say I have a 4TB USB SSD from a few years ago, that's been sitting unpowered in a drawer most of that time. How long would it need to be powered on (ballpark) for the full disk refresh to complete? Assume fully idle. (As a note: I do have a 4TB USB SSD which did sit in a drawer without being touched for a couple of years. The data was all fine when I plugged it back in. Of course, this was a new drive with very lo…

More certain to just do a full read of the drive to force error correction and updating of any weakening data.

noob question... how do i force a full read?

Re: Unpowered SSDs slowly lose data

#153

Post by bullen »

karczex wrote: post #142
userbinator wrote: post #77

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 de…

That's how it has to work. To increase capacity you have to make smaller cells where charge may easier diffuse from one cell to another. Also to make drive faster, stored charge has to be smaller, which also decrease endurance. With SLC and QLC comparison is even worse as QLC is basically clever hack to store 4 times more data in the same number physical cells - it's tradeoff.

Yes, but that tradeoff comes with a hidden cost: complexity!

I much rather have 64GB of SLC at 100K WpB than 4TB of MLC at less than 10K WpB.

The spread functions that move bits around to even the writes or caches will also fail.

The best compromise is of course to use both kinds for different purposes: SLC for small main OS (that will inevitably have logs and other writes) and MLC for slowly changing large data like a user database or files.

The problem is now you cannot choose because the factories/machines that make SLC are all gone.

Re: Unpowered SSDs slowly lose data

#154

Post by bullen »

RachelF wrote: post #83
userbinator wrote: post #77

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 de…

Endurance going down is hardly a surprise given that the feature size has gone down too. The same goes for logic and DRAM memory. I suspect that 2035 years time, hardware from 2010 will work, while that from 2020 will be less reliable.

I concur; in my experience ALL my 24/7 drives from 2009-2013 still work today and ALL my 2014+ are dead, started dying after 5 years, last one died 9 years later. Around 10 drives in each group. All older drives are below 100GB (SLC) all never are above 200GB (MLC). I reverted back to older drives for all my machines in 2021 after scoring 30x unused X25-E on ebay.

The only MLC I use today are Samsungs best industrial drives and they work sort of... but no promises. And SanDisc SD cards that if you buy the cheapest ones last a surprising amount of time. 32GB lasted 11-12 years for me. Now I mostly install 500GB-1TB ones (recently = only been running for 2-3 years) after installing some 200-400GB ones that work still after 7 years.

Re: Unpowered SSDs slowly lose data

#155

Post by londons_explore »

userbinator wrote: post #77

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 de…

I'm sad that drives don't have a 'shutdown' command which writes a few extra bytes of ECC data per page into otherwise empty flash cells.

It turns out that a few extra bytes can turn a 1 year endurance into a 100 year endurance.

Re: Unpowered SSDs slowly lose data

#156

Post by fainpul »

geokon wrote: post #152
gblargg wrote: post #136

Earlier quoted context omitted.

More certain to just do a full read of the drive to force error correction and updating of any weakening data.

noob question... how do i force a full read?

On macOS / Linux you can use `dd` to "copy" everything from /dev/yourssd to /dev/null. Just be careful not to do it the other way!

https://www.man7.org/linux/man-pages/man1/dd.1.html

I have no idea if forcing a read is good / the right way. I'm just answering how to do it.

Re: Unpowered SSDs slowly lose data

#157

Post by breput »

The spinrite[0] user group has noticed some of these effects, even on in-service drives.

The theory is that operating system files, which rarely change, are written and almost never re-written. So the charges begin to decay over time and while they might not be unreadable, reads for these blocks require additional error correction, which reduces performance.

There have been a significant number of (anecdotal) reports that a full rewrite of the drive, which does put wear on the cells, greatly increases the overall performance. I haven't personally experienced this yet, but I do think a "every other year" refresh of data on SSDs makes sense.

[0] https://www.grc.com/sr/spinrite.htm

Re: Unpowered SSDs slowly lose data

#158

Post by homebrewer »

geokon wrote: post #152
gblargg wrote: post #136

Earlier quoted context omitted.

More certain to just do a full read of the drive to force error correction and updating of any weakening data.

noob question... how do i force a full read?

the most basic solution that will work for every filesystem and every type of block device without even mounting anything, but won't actually check much except device-level checksums:

  sudo pv -X /dev/sda
or even just:

  sudo cat /dev/sda >/dev/null
and it's pretty inefficient if the device doesn't actually have much data, because it also reads (and discards) empty space.

for copy-on-write filesystems that store checksums along with the data, you can request proper integrity checks and also get the nicely formatted report about how well that went.

for btrfs:

  sudo btrfs scrub start -B /
or zfs:

  sudo zpool scrub -a -w
for classic (non-copy-on-write) filesystems that mostly consist of empty space I sometimes do this:

  sudo tar -cf - / | cat >/dev/null
the `cat` and redirection to /dev/null is necessary because GNU tar contains an optimization that doesn't actually read anything when it detects /dev/null as the target.

Re: Unpowered SSDs slowly lose data

#160

Post by bullen »

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…

Ok, so all bits have to be rotated, even when powered on, to not loose their state?

Edit: found this below: "Powering the SSD on isn't enough. You need to read every bit occasionally in order to recharge the cell."

Hm, so does the firmware have a "read bits to refersh them" logic?

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