[wtallis]

> because flash memory loses data over time if it's powered-off.

That's a red herring; the magnitude of this effect is usually greatly exaggerated, and in reality never comes close to being as important as the fact that flash memory is simply too expensive to use for cold storage.

And of course, the very idea of cold storage is dangerous: if you really want to ensure your data lasts for decades, you should be verifying your backups at least annually and making plans to migrate your data off any media that is obsolete and at risk of becoming hard to read using commodity hardware. This also entirely eliminates the above flash memory data retention concerns.

[throw0101b]

> That's a red herring; the magnitude of this effect is usually greatly exaggerated […]

Per JEDEC, Client SSDs have to retain data for 1 year at 30C, and Enterprise SSDs have to retain data for 3 months at 40C:

* https://www.jedec.org/sites/default/files/Alvin_Cox%20[Compa...

I'm sure most last longer, but as a CYA I wouldn't want to rely on that.

[wtallis]

That's the standard for drives that are at end of life, having exhausted their rated write endurance. Those aren't the drives anyone would use for a cold storage backup system. Drives that have only been written to a few times will retain data much longer.

[gymbeaux]

I remember reading something somewhere about a guy doing tests on "3D" NAND and other TLC/MLC NAND SSDs and finding that data was lost well before the "10 years or so" that we have come to assume unpowered SSDs can retain data for. I can't locate that article at the moment but it isn't unreasonable to expect faster degradation on denser NAND.

[wtallis]

The 3D in 3D NAND doesn't belong in scare quotes; the physical arrangement of the memory cells really is three-dimensional and it isn't just a marketing term. The transition from planar NAND to 3D NAND turned back the clock by several years in terms of shrinking memory cell volume and charge differences between adjacent data states.

The SSDs that caught the most flak for poor retention characteristics were using the last generation of planar NAND, in a three bit per cell configuration, which in hindsight was a bit of an overreach. But even then, the worst symptoms that could be reliably reproduced were poor performance reading back stale data, a result of the drives having to use higher levels of ECC to recover the data. (More recent SSDs have vastly more powerful controllers capable of running LDPC calculations much faster.) That's not quite the same as losing data.