@Guido
When you create a data disk either during VM creation or after it is presented as an unformatted disk the disk needs to be formatted and mounted before it can be used. Instructions for that can be found here.
After the disk has been formatted and mounted and /etc/fstab updated the mount should persist on reboot. You can then create a managed image and future vms will have this data disk and home directory already mounted on boot.
Hope this helps! Let me know if you run into issues or still have questions.
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