--allow-missing-source=true - what's goal of this?

I have a backup with one source like “S:\2018”, but disk S may be not mounted and I try to use “–allow-missing-source=true” parameter. I was in shocked when I knew that my files was deleted!

Why?))) And that goal of this parameter?

P.S. I use “–run-script-before-required” but it not better because it show me error every day (as I scheduled).

This github issue describes the function and purpose pretty well Backup error: The source folder does not exist, aborting backup · Issue #2760 · duplicati/duplicati · GitHub

Essentially the missing folders will just not be part of any snapshots where it wasn’t plugged in.

For an external drive I would recommend setting up a new job for just that backup and then either manually backing up that drive when it’s plugged in or scheduling it and ignoring the errors that job throws. Duplicati does not do disconnected drives that well currently.