Others can weigh in here…
But in my mind there are three data sets to worry about, and what your goal is.
- The entire system, so you can roll back or fix a broken system drive.
- All the interesting configuration files for reference, and all the user/app data
- Just the user/app data
What I’m not certain about is, whether you could boot of a different drive and rsync back your NAS to your boot drive and re-establish a working system. Also keeping in mind that rsync does not keep any history, but is always just the latest, possibly too recent to recover from a failure.
For full system recovery, an actual disk snapshot seems like a more foolproof way of doing that, rather than a filesystem level rsync.
That said, and rsync of your user’s home folder, plus any data drives you have mounted, maybe even the /opt file tree with all the apps is totally usable. In that case you quickly re-install a virgin OS and rsync all the non-OS data back in, and it should fit.
That leaves a gap with all the little changes we make to the OS (tweaks, mounts, etc.). While they may not rsync back cleanly, having a copy of files like /etc/fstab for reference so you don’t do it from scratch is super valuable. As snapshots are in-time, you could keep a few of thema round for different check points.
Mac TimeMachine is great for restoring a borked OS. But that’s because it’s tightly integrated with the recovery function in the boot loader. I’m not sure if there’s a good Rocky equivalent?
PS: Was looking more into that. I’ve come across a few articles that describe full system backup/recovery with rsync. However, it think they assume the OS lives on a single disk. My Rocky 8.7 seems seems to be split over 3 filesystems (root, home, and boot). So you would have to rsync them separately, or your system will look differently afterwards. You also have to restore the LVM config on the drives.
So yes, rsync might be able to do full system recovery on a straightforward single, non-LVM disk config.