How do you do that? My naive idea: Download 100 TB every 3 month to a 2nd device, create a list of files restored, validate checksums with the original machine

How do you do that? My naive idea: Download 100 TB every 3 month to a 2nd device, create a list of files restored, validate checksums with the original machine, make a list of files differing and missing, check which ones are supposed to be missing? That sounds like a full time job.