Various different ways for various different types of files.

Anything important is shared between my desktop PC's, servers and my phone through Syncthing. Those syncthing folders are all also shared with two separate servers (in two separate locations) with hourly, daily, weekly, monthly volume snapshotting. Think your financial administration, work files, anything you produce, write, your main music collection, etc... It's also a great way to keep your music in sync between your desktop PC and your phone.

Servers have their configuration files, /etc, /var/log, /root, etc... rsynced every 15 minutes to the same two backup servers, also to snapshotted volumes. That way, should any one server burn down, I can rebuild it in a trivial amount of time. This also goes for user profiles, document directories, ProgramData, and anything non-synced on windows PC's.

Specific data sets, like database backups, repositories and such are also generally rsynced regularly, some to snapshotted volumes, some to regulars, depending on the size and volatility of the data.

Bigger file shares, like movies, tv-shows, etc... I don't backup, but they're stored on a distributed GlusterFS, so if any one server goes down, that doesn't lose me everything just yet.

Hardware will fail, sooner or later. You should see any one device as essentially disposable, and have anything of worth synced and archived automatically.