what is the best way to monitor bandwidth on virtualhosts?

there is no good way, you have to use several methods including mrtg, access logs, statistics such as webalizer, using server-status.

The only way to get a good picture is if you use one ip per domain.

Hy,

for the apache we're using a special log file (our traffic log). This file is parsed every 2 hours and the data is imported into a SQL Database for faster querys.

In this log file we only log the virtual_host, the month, the year and the bytes from the request.

This is not perfect but i think a good way to handle multiple vhosts on one ip.

Greetings
Oliver