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.
Look at setting up a SnapRAID drive for data redundancy. SnapRAID needs to be as big as or bigger than your largest data drive. It works best with data that isn't deleted or changed often. And if you do, then dual parity helps a lot in that regard.
But your best option is either using Drivepool duplication feature or just backup your data periodically to some external drive or cloud.
Kind of pointing out the obvious here but there are 20 and 22TB drives where you can back it up to.
As it was mentioned, you can implement SnapRAID for redundancy and better data availability. Since you are running your system on Windows, it might make some sense for you to use Backblaze personal as a cloud backup https://www.backblaze.com/cloud-backup/personal
Also, try to have a local backup somewhere (external drive or backup NAS)
Buy the cheapest $/TB drives you can find (still from reputable places). Give them a 1 or 2 full write cycles to check, especially when 2nd hand. And copy all the data to them. It is the easiest and cheapest solution for media or large picture libraries.
At least you have an offline copy that way. If possible store it also in a seperate building.
For documents and my very best pictures, I use OneDrive.