I have 3 layers:
Online: A big BTRFS "raid 1" (block-based mirroring) array. This is what Plex runs off of. If I lose a drive, I just replace it and rebalance. I run btrfs scrubs weekly.
Offline: I have a WD external hdd with a plain old ext4 hdd that I rsync all files to weekly. If my btrfs array shits itself, I just copy back over from this hdd.
Emergency: If the above process doesn't work (say: the external hdd is dead when I go to restore from it, or I can't physically find it, or my house floods and everything in the basement is lost, etc), then my fallback is:
I sync all truly critical stuff that can't be replaced (so, basically just family pics and videos) to S3 as deep archive storage class. Costs pennies. I don't do any fancy tar/archiving, encrypting, or compressing (since video and image files are generally already compressed). I figure the risk of people snooping at our family pics is smaller than the risk of me needing to restore from a backup and not being able to because of stupid reasons (lost gpg key, some kind of problem with tar, etc).
This is small, since most of my disk use is from things like rips I've made of BluRay/DVD's, FLACs from bandcamp or rips of music CD's, etc. Things I can recover with appropriate effort.