I think im getting closer and closer to the cause.
So i got this:
1.1G    /home/speedservi
1.2G    /home/bmdzuid/domains/bmdzuid.nl/public_html/wp-content
1.3G    /home/bmdzuid
1.3G    /home/bmdzuid/domains
1.3G    /home/bmdzuid/domains/bmdzuid.nl
1.3G    /home/bmdzuid/domains/bmdzuid.nl/public_html
1.4G    /home/qupra/domains/qupra.nl/logs
1.8G    /home/qupra
1.8G    /home/qupra/domains
1.8G    /home/qupra/domains/qupra.nl
2.5G    /usr
6.1G    /home
9G     /
Then i start backup for all domains one by one and nothing strange happens untill i backup especially this one site. 
www.speedservice.nl
Then i get this:
1.1G    /home/speedservi
1.2G    /home/bmdzuid/domains/bmdzuid.nl/public_html/wp-content
1.3G    /home/bmdzuid
1.3G    /home/bmdzuid/domains
1.3G    /home/bmdzuid/domains/bmdzuid.nl
1.3G    /home/bmdzuid/domains/bmdzuid.nl/public_html
1.4G    /home/qupra/domains/qupra.nl/logs
1.8G    /home/qupra
1.8G    /home/qupra/domains
1.8G    /home/qupra/domains/qupra.nl
2.5G    /usr
5.8G    /var/log/httpd
5.8G    /var/log/httpd/domains
5.9G    /var/log
6.1G    /home
6.4G    /var
16G     /
So when the domain 
www.speedservice.nl is going to be used. The server created insane log files.
This site is just a plain and simple WordPress site. Me myself manage the site aswell and there are no plugins that i don't use at other sites that cause this.
Can logging files be disabled ??