Expected life with NAND based devices *unpowered*

[Elixer]

Long story short, one lady had 5 USB flash devices from all different makers (kingston, sandisk, OM brand, OD brand, Staples brand) 3 microSD cards, 2 SD cards, and a DVD+R and those were all in a safe deposit box for 17 months.
When she went to access them, only 2 of the USB flash devices had anything on them, the rest were 'raw'. Two microSD and two SD cards were fine, as was the DVR+R.
I cloned them, and tried to find any data, and it was just some random garbage, nothing that could be pieced together again without some serious dedication in trying to recover anything that even resembles the source.
Heck, lots of the data was gibberish, no file headers, no known file markers, just one big piles of bits.
She had tax records (pdfs), tons of pictures, and other video & audio recordings.
The ones that were OK were Kingston, and the Staples branded USB flash drive, 1 Toshiba & 1 Canon branded SD cards, 1 Sandisk & 1 PNY microSD.
Now, by OK, I mean they still could be accessed.
As she was looking as some pictures, some of them were slightly corrupted.

I know it was said before the NAND devices are supposed to keep their data in an unpowered state for a few (5+?) years, but it seems degradation of data is going on in as little as 17 months.
I can verify that the source images were intact and the time though, they didn't make hashes of the files.

For the stuff that is still good, I now have made full PAR2 recovery information on those, and those are burned to 8 DVDs, as well as a 2.5" HD.

Anyone else experience anything like this before?
Somehow, I don't think this is a rare case, and more and more people who have these devices stored away someplace are going to see that they have degraded on them.

 

[Matthiasa]

Yeah I've had similar happen to on of my flash drives, nothing important was on it however. They aren't really designed for long term data storage, and need to be powered on every so often to prevent data loss.

 

[BSim500]

I haven't experienced it myself but it's far from rare and there is a woeful lack of serious testing on unpowered data retention of flash / SSD's by tech sites in general.

Usual advice applies : Don't make "a" backup, make at least 2-3. Likewise, mechanical HDD's & optical discs are far from dead for reliable backups intended to last more than 1 year. I have a 17 year old CD-R somewhere which can be read just fine.

 

[Hellhammer]

The typical cheap USB drives and SD cards use garbage-grade NAND to put it bluntly, and the controllers also lack proper ECC to correct a high number of errors. In other words, data retention may actually be much shorter compared to SSDs that use much higher quality NAND.