IIRC, the writers for M-DISCs are special, but the reader can be any DVD or Blu-ray drive.

Honestly, I think the biggest consideration for digital archival media isn't so much the longevity of the media, but the future availability of equipment to read it.

That's one of the biggest benefits of paper, IMHO. Besides being very well-understood material, nearly everyone is born with the necessary reading equipment and the decoding software is very common.

[Citation needed]

https://en.wikipedia.org/wiki/Literacy

There you go.

Because some people can’t read. Har har har :)

>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...

TL;DR: The CD-R's didn't survive the process, but the M-discs did, with their data intact.

Are they still produced?

Thanks!