I initially stored my ownCloud data on an external NTFS hard disk. (Yes, this was not a good idea at all.) After some time now I wanted to move the files to a bigger ext4 drive on the same machine. Unluckily there are many posts and articles that are really irritating on the Internet, such as: 1, 2, 3, 4. At least I found some promising hints at the official GitHub forums (this and that) and gave it a try: