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datahoarder
Who are we?
We are digital librarians. Among us are represented the various reasons to keep data -- legal requirements, competitive requirements, uncertainty of permanence of cloud services, distaste for transmitting your data externally (e.g. government or corporate espionage), cultural and familial archivists, internet collapse preppers, and people who do it themselves so they're sure it's done right. Everyone has their reasons for curating the data they have decided to keep (either forever or For A Damn Long Time). Along the way we have sought out like-minded individuals to exchange strategies, war stories, and cautionary tales of failures.
We are one. We are legion. And we're trying really hard not to forget.
-- 5-4-3-2-1-bang from this thread
I believe you're approaching this from the wrong angle - this isn't a tech problem, this is a people problem.
Instead of trying to get media that can last 200+ years, just teach your kids and grandkids the importance of keeping your family legacy alive. This will be way more effective than any medium you can come up it. Storage technologies change but the data remains the same, the future generations should be able to gradually upgrade storage mediums as necessary so the information keeps existing.