Immutable Nixos. My entire server deployment from partitioning to config is stored in git on all my machines.
Every time I boot all runtime changes are "wiped", which is really just BTRFS subvolume swapping.
Persistence is possible, but I'm forced to deal with it otherwise it will get wiped on boot.
I use LVM for mirrored volumes for local redundancy.
My persisted volumes are backed up automatically to B2 Backblaze using rclone. I don't backup everything. Stuff I can download again are skipped for example. I don't have anything currently that requires putting a process in "maint mode" like a database getting corrupt if I backup while its being written to. When I did, I'd either script gracefully shutting down the process or use any export functionality if the process supported it.