I use Arq Backup on my workstations, along with Resilio Sync. The NAS holds all our media/documents/music/whatever, and where possible, this gets auto uploaded

I use Arq Backup on my workstations, along with Resilio Sync. The NAS holds all our media/documents/music/whatever, and where possible, this gets auto uploaded from workstations to the NAS, mostly through Resilio Sync, but also ChronoSync. A local Raspberry Pi (different building) acts as a node in the Resilio Sync setup, adding more redundancy. The NAS backs up to a local USB drive nightly, as well as a remote (4km distance) Odroid HC2 with a WD Red drive. This device also runs Resilio Sync as a redundant node. All machines run Btrfs where possible, with smart monitoring, daily short smart tests, weekly long smart tests, monthly scrubs, and log monitoring emailed to my inbox every morning. Finally i make yearly archive discs (100GB M-Disc) with the data from the past 12 months. I burn these in 2 copies, one is stored locally, the other is stored remotely. Along with these drives, i also maintain a couple of 4TB USB3 drives, which i freshen (nondestructive badblocks) yearly, and update. Again, one is stored locally, the other remotely with the M-discs. Even with the above setup, there is a theoretical possibility of losing data, but as most data lives on both the NAS and the client machines, as well as a remote target, i would need to lose all 3 at the same time. The only irreplaceable data would be our family photos, and those are also stored on optical and magnetic media (spending 360/365 days powered off), adding at least a couple more layers of redundancy to the equation.