I run linux for everything, the nice thing is everything is a file so I use rsync to backup all my configs for physical servers. I can do a clean install, run my setup script, then rsync over the config files, reboot and everyone's happy.

For the actual data I also rsync from my main server to others. Each server has a schedule for when they get rsynced to so I have a history of about 3 weeks.

For virtual servers I just use the proxmox built in backup system which works great.

Very important files get encrypted and sent to the cloud as well, but out of dozens of TB this only accounts for a few gigs.

I've also never thrown out a disk or USB stick in my life and use them for archiving, even if the drive is half dead as long as it'll accept data I shove a copy of something on it, label and document it. There's so many copies of everything that it can all be rebuild if needed even if half these drives end up not working. I keep most of these off-site. At some point I'll have to physically destroy the oldest ones like the few 13 GB IDE disks that just make no sense to bother with.