In Chapter https://docs.linuxmuster.net/de/v7.3/installation/install-from-scratch/basis_server.html#speicher-des-systems while configuring the storage layout the documentation recommends to leave the second partition configured.
In Chapter https://docs.linuxmuster.net/de/v7.3/installation/install-from-scratch/basis_file_server.html the installation of ubuntu should be done like in chapter basis_server. The instructions assume that the second partition is already configured. This causes confusion. See here: https://ask.linuxmuster.net/t/lmn-7-3-fileserver-nachtraeglich-einbinden/11822/5