Well, I've now hung up the backup hard drive. That is the only one that is addressed by the rsync job. Then my / srv looks like this:
I cannot say whether there is a swap file in the root directory of 5.1GB. I have deliberately not set anything corresponding. Should have been preset if that.
The Size of the Harddisk is 64GB, system show 50GB.
This is the output of du -xhd1 /var: