I have a git repository configured on my local NAS with documents sorted in folders based on information category. Electronic documents are copied, physical documents are scanned. The repository has an active-active backup that's updated daily through an rsync script. This repo is also cloned on multiples of my day-to-day devices. Such a workflow ensures the following:

1) Any machine I use is only a pull away from the latest

2) Having a repo lets me track history and use search functionality based on repo tags. It also provides versioning for documents.

3) Each clone on each machine acts as its own backup.

4) The NAS is mirrored, the active backup is also mirrored.