If you are going to host more than 300 domains or Web sites on your server, you should switch on support for piped logs in the Apache Web server. To do this, follow these steps:
/usr/local/psa/admin/sbin/websrvmng -a -v
This will allow to host about 900 domains/Web sites. If you need to host more than 900 domains/Web sites, then you will need to recompile Apache and some other system packages, as described in the online knowledge base article at http://kb.parallels.com/en/260.