My PCs always have 2 identical sized drives in them and I periodically clone Drive C (the only one used) to Drive D. If anything ever goes wrong, it's just a quick reboot to the 2nd drive and I'm back up and running until I figure out what happened to the C Drive. I used Acronis TrueImage and set it clone when I go to sleep, but even for near full 1TB drives, it only takes a couple of hours to clone a drive. I love that program.
I don't do the cloning as often as I should though, it might be 3 months between doing it again, so recently I started using a file sync program for just a few directories like documents, Calibre library, and my photos, and I sync those nightly across my LAN. After trying out quite a few programs, the one I like the best is
FreeFileSync. Not only is it free, but it's easy to use, you can have it constantly monitor certain directories and sync them constantly, or run it when you want, or what I do is have it set as a Windows Task to do nightly. It can sync just from one PC to others (my main use), or sync both ways between 2 PCs. Here's 2 sites that give good explanations how to use the program:
Automatic Backup with FreeFileSync
Replace SyncToy with FreeFileSync