Ok, seems /var/log/ was also included into this quota calculation.
Is it true, that quota recognize any file (on whole file structure) that is “owned” by “root”?
Yes, files “owned” by a user, including the root user, are attributed to that user’s disk usage. If a quota is set for the root user (which is uncommon, as root often needs unrestricted access to ensure system functionality), then files owned by root would count towards root 's quota.
There wasn’t add a quota for my root-user, but the disc was full.
I’ve seen that a huge amout of filesize are assigend to “root” user in the backend overview in webmin.
And after checking /root I just wonder where those huge amount of used space are regarding to…
… know I know, thanks.
Found in /var/log/fail2ban a file > 21 GB which was the cause.