OCP Files NotFoundException after setting datadir

The mount command return an error with the option for uid and gid, so I have to rule this out.

Sorry, but I’m not entirely sure of what you mean with this, and from the man page of mount I was unable to retrieve anything about it,

The USB disk is formatted in ext4, trying with NTFS was even worse.

That looked strange for me too, but I guess it was worth trying also that way just to be sure.