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Unpowered SSDs slowly lose data

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Re: Unpowered SSDs slowly lose data

#141

Post by spoaceman7777 »

fsckboy wrote: post #123
spoaceman7777 wrote: post #120

A solution I haven't yet seen in this thread is to buy multiple drives, and sacrifice the capacity of one of those drives to maintain single parity via a raidz1 configuration with zfs. (raidz2 or raidz3 are likely better, as you can guard against full drive failures as well, but you'd need to increase the number of drives' capacity that you're using for parity.) zfs in these filesystem-specific parity-raid implementa…

this is about drives that are not plugged in. are you saying parity would let you simply detect that the data had gone bad? increasing the number of drives would increase the decay rate, more possibilities for a first one to expire. if your parity drive expired first, you would think you had errors when you didn't yet.

No, I'm talking about parity raid (raidz1/z2/z3, or, more familiarly, raid 5 and 6).

In a raidz1, you save one of the n drives' worth of space to store parity data. As long as you don't lose that same piece of data on more than one drive, you can reconstruct it when it's brought back online.

And, since the odds of losing the same piece of data on more than one drive is much lower than the odds of losing any piece of data at all, it's safer. Upping it to two drives worth of data, and you can even suffer a complete drive failure, in addition to sporadic data loss.

Re: Unpowered SSDs slowly lose data

#142

Post by karczex »

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.

Re: Unpowered SSDs slowly lose data

#143

Post by octorian »

markhahn wrote: post #80
canadiantim wrote: post #73

What is the best way to store data for a long time then?

all the major players say "tape". (but that's partly for practical issues like scaling and history)

And yet nobody wants to actually offer a tape-based solution that's practical, easy to get, holds enough data, and doesn't cost a blithering fortune.

Even if you are willing to spend that small fortune, good luck actually getting all the parts together without enterprise contracts.

Re: Unpowered SSDs slowly lose data

#144

Post by kasabali »

gruez wrote: post #53
zozbot234 wrote: post #51

Earlier quoted context omitted.

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.

Cheap DRAM-less controllers usually wait until the drive is almost full to start folding. And then they'll only be folding just enough to free up some space. Most benchmark results are consistent with this behavior.

Re: Unpowered SSDs slowly lose data

#145

Post by lofaszvanitt »

ziml77 wrote: post #129
nirui wrote: post #118

Earlier quoted context omitted.

The simplest trick is just don't use SSD for long term backup, use a normal magnetic hard drive instead, those thing way lasts _longer_ (but not forever, even in human timescale). I have a HDD that was 17+ years since it last powered on. I dug it out recently to re-establish some memories, and discovered that it still reads. But of course you need to take care of them well, put them in an Anti-Static Bag or something…

I'm seeing threads where even for HDDs people are recommending you mount them yearly to do a full check of the data and to ensure that everything keeps moving freely.

Superstition....

Re: Unpowered SSDs slowly lose data

#147

Post by userbinator »

lotrjohn wrote: post #108
RachelF wrote: post #83

Earlier quoted context omitted.

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.

Completely anecdotal, and mostly unrelated, but my NES from 1990 is still going strong. Two PS3’s that I have owned simply broke. CRTs from 1994 and 2002 still going strong. LCD tvs from 2012 and 2022 just went kaput for no reason. Old hardware rocks.

LCD tvs from 2012 and 2022 just went kaput for no reason.

Most likely bad capacitors. The https://en.wikipedia.org/wiki/Capacitor_plague may have passed, but electrolytic capacitors are still the major life-limiting component in electronics.

Re: Unpowered SSDs slowly lose data

#148

Post by danparsonson »

spoaceman7777 wrote: post #140
fweimer wrote: post #122

Earlier quoted context omitted.

How would this work? Wouldn't all these drives start loosing data at roughly at the same time?

Yes, but different pieces of data. The stored parity allows you to reconstruct any piece of data as long as it is only lost on one of the drives (in the single parity scenario). The odds of losing the same piece of data on multiple drives is much lower than losing any piece of data at all.

But the data is not disappearing, it's corrupted - so how do you know which bits are good and which are not?

Re: Unpowered SSDs slowly lose data

#150

Post by Springtime »

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…

In the longer JEDEC overview document[1] it explains that in the ideal 'direct' testing method retention testing is only performed after the endurance testing. Which is only after the drive has had its max spec'd TBW written to it.

While if the endurance testing would exceed 1000 hours an extrapolated approach can be used to stress below the TBW but using accelerated techniques (including capping the max writable blocks to increase wear on the same areas).

Which is less dramatic than the retention values seem at first and than what gets communicated in articles I've seen. Even in the OP's linked article it takes a comment to also highlight this, while the article itself only cites its own articles that contain no outside links or citations.

[1] https://www.jedec.org/sites/default/files/Alvin_Cox%20%5BCom...

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