I have backed up my Pi a number of times with the SD Copier utility with both the Pi running and while it's running weewx. I always test the backup SD after creating it and it's never failed. Perhaps backing up an operational system "live" isn't the wisest thing to do, but it worked for me 5-6 times or more.
I do have daily cron jobs backing up any custom scripts, config files, etc. and the database to a NAS, but that's just in case I mess them up with an edit mistake, etc. The SD Copier is, I'm pretty sure, a bit-per-bit dd backup of the SD card and probably only needs to be done after major upgrades. My thought process is that if the operational SD card gets corrupted, you can swap in SD Copier created backup, restore weewx.sdb from "yesterday" and be back in operation on less than 30 minutes.
- Paul VE1DX