Sorry for my delay. Meanwhile I’m in my easter holidays:grinning:.
This evening I solved my problem by the assistance of the following support article: Resize LVM on UCS
After entering the command lsblk I saw that there is indeed a 100G disk and I had to extend the lvm group.
root@owncloud-01:/usr/bin# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
fd0 2:0 1 4K 0 disk
sda 8:0 0 **100G** 0 disk
├─sda2 8:2 0 1K 0 part
├─sda5 8:5 0 49,5G 0 part
│ ├─vg_ucs-swap_1 254:1 0 2G 0 lvm [SWAP]
│ └─vg_ucs-root 254:0 0 47,5G 0 lvm /
└─sda1 8:1 0 487M 0 part /boot
root@owncloud-01:
Thanks for your support.