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The 3-2-1 rule
(alien.top)
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 (tm) ). Along the way we have sought out like-minded individuals to exchange strategies, war stories, and cautionary tales of failures.
I do main data at home, external HD as backup offsite (I update maybe 1-2x a year otherwise it's turned off/unplugged), and any new files not on the backup are in cloud storage + local HD, separate from main data.
If either drive failed I'd just order a new one since the odds of both failing within a couple days would be low.