Ohhh, that’s new for me, that btrfs advantages are not compatible with VBox. Thank you for your quick and engaged reply!
Before I am going to invest too much time in a non functioning experiment, I want to ask:
If I keep VBox software on my BTRFS based Manjaro and then add an additional harddisk which is ext4 formatted and will contain all my *.vdi images, do you think, that VBox can work with these VMs?
Or is it strictly necessary, that not only the VMx but also VirtualBox Software must run on another FS than BTRFS?