I wanted to know if anyone had any suggestion on a tool that I can monitor spikes in the server's traffic usage with many virtual hosts setup.
I want something I can look at many hrs or days later to see where the spike occurred or which vhost etc..
I'd like to also be able to see how much bandwidth and hits a website is getting.

I don't know if you've heard about Awstats but it does all of that by monitoring the web server logs. I've used it with Apache with great success.

It can tell you the bandwidth used by any domain configured per day and has totals, averages, etc. It also shows hits, unique visitors, pages, visits, etc.

It's far from perfect (as are most other traffic analysing tools), but it gets the job done for me. If you want to monitor traffic that passes outside of the web server you'll have to use another tool.

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Working well now thanks