I also came across M-Disc but iirc there is no real verification of the longevity claims outside of marketing from the manufacturer. >The second choice is usin

I also came across M-Disc but iirc there is no real verification of the longevity claims outside of marketing from the manufacturer. >The second choice is using hard drives (easily available) and every so often power them up and copy data to new drives. I suppose the question is whether doing so could remain under the error correction threshold indefinitely, since there will be errors accumulating both during copying and over time in cold storage. If manufacture of new drives stops, it also isn't clear to me if only the data stored on them has a 30 year life or if the medium itself decays regardless of whether it is in use or not. In theory I imaging keeping an unused NAND or even magnetic drive in cool dry storage should preserve it's physical integrity indefinitely...