Puuh ... this was a tough piece of work.
When I reinstalled OMV 4.x, I disconnected (put cable off) all data-disks, only my system-M2 was already active ... installation was just fine, no problem. Then I reconnected all drives and then there was a bad surprise - grub was not loading my new installation; every time, I connected a data disk, a error similar like this (No init found. Try passing init=bootarg.) appeared: https://askubuntu.com/question…itramfs-error-during-boot
I found out, that my installation-USB-Stick was ! sda ! [wrong mount order] during installation, so grub put no boot-partition/-information on sda (my M2) after I removed the USB-Stick.
I found the solution (fix grub2) in this blog: https://dcandy.wordpress.com/2…ls-to-install-bootloader/
Finally, I looks quite fine to me ... OMV is reachable, data is already there ... hope this will last for a long time
Thank you for your support!