could you try to use "-x" with the "du" command to limit the calculation to the "/" filesystem like: "du -hx /z" to check how much space below /z is on the / filesystem and not on the drives mounted below. Example: I have /boot/efi on a separate FS (like probably most that run UEFI) # du -sh /boot 106M /boot (this was /boot + /boot/efi) # du -shx /boot 100M /boot # du -sh /boot/efi/ 5,3M /boot/efi/