Comment by Springtime 10 days ago
While I think common digital media outlasting analog forms in terms of integrity over long periods of time is unrealistic I do have 40 year old CDs from 1984 that are still bit perfect as of just a couple years ago (verified against online checksum databases for the same releases), so it'll be interesting seeing how long they last.
There was a period of time where pressed CDs were manufactured poorly, with the aluminum layer inside exposed to the outside, resulting in corrosion over time and loss of readability on those CDs.
Overall, though, properly-made CDs, handled carefully, have been excellent at storing data long-term.
But while this is nice enough I guess for storing individual musical albums long-term, it's not practical for storing truly large volumes of arbitrary data. CD-Rs and CD-RWs have not had the same durability demonstrated at all (quite the opposite in fact). DVDs are better at almost 4GB per disc, but here again only the factory ones are actually durable, and 4GB isn't going to store much these days, perhaps one movie with high lossy compression.
While my comment wasn't about the feasibility of pressed CDs for a mass blackout event but just an example of long-term integrity of existing digital media, it's unfortunate that a forum (MyCE) dedicated to tracking integrity of user-writable optical discs unexpectedly closed a couple years ago due to the webmaster pulling the plug.
It had users who carefully performed benchmarks on media for more than a decade to see which types and makes held up best over time, along with best practices. Few have the interest or patience for such things so it's unfortunate to just have such info vanish.
I will add though that what's missing from the discussion is Blu-Ray, which allows up to 128GB per disc. (I only vaguely recall reading some critique of BD DL discs so can't say how it might compare long term though, apart from the greater cost at such capacities.)
Somehow it seems ironic that a forum dedicated to understanding the long-term viability of data storage, an important topic lately because of the unreliability of 3rd-party providers (like cloud companies), itself became a victim of the unreliability of its own webmaster.
128GB BD-R discs do exist, but at $219 on Amazon for 25 discs, that's about $0.07/GB. It would be MUCH cheaper to just buy a stack of refurbished enterprise-class HDDs and store your data on those, in triplicate, with a filesystem that has error correction (like ZFS). Personally, I would bet on HDDs used this way still being readable and not having bit-rot after 50 years over 4-layer BD-R discs.
Pressed CDs are pretty good in terms of durability, but how are you gonna get one produced in a single day? (Per the prompt, the Internet disappears tomorrow, not in a couple of weeks.)