I try to make my external hard disk a permanant one on a Raspberry Pi 3 b+. After editing the fstab file, It was working. However I don't know why but some times the hard disk which name is DiskExt/ change to DiskExt_/. The OS that is install on the Raspberry is OSMC.
This often happens after an unclean eject incident. If you remove the disk without unmounting it (or the disk resets due to a power outrage), its original mount point may remains busy. When the disk is later replugged (or the power is restored), it will be mounted again. Many mount scripts are instructed to pick a different name, often by adding a suffix like
_, if the original mount point is already in use.