Thanks for the quick reply.
yes, I rebooted and I can see the additional spave already.
So I changed the policy to most free space, but it still does not work.
Do I need to create the folders I have merged with my unionfs manually?
Example: I have a shared folder "Movies", which exists on the older two drives. Do I need to create this fold on the new HDD manually - and do I need to set the permissions manually?
Thanks for your help.