The one that went wrong was yesterday. I tried to copy some stuff from a share on a USB drive to the internal one. At some point it seems as if the USB drive disconnected leaving the shared folder pointing to /. So it started copying a lot of stuff from / to my internal NAS partition. But only reading, never writing.
The last rsync was an attempt to have deltacopy on Windows as server and pull from there.
rsync -avz mh@192.168.1.4::Downloads /media/UUID/Downloads
Ownership wrong?
Thanks for helping