jeffatrackaid - 6:31 pm on Jan 28, 2009 (gmt 0)

You will want to use sysstat to start tracking disk/cpu/memory metrics. Then have an external tool poll certain pages on your site to generate a baseline of response. This way you can clearly track your progress.

I typically start with MySQL.

There is a tool called mysqltuner.pl that can give you some initial indications of problems but it is no substitute for having handle on MySQL tuning.

Sysstat is very useful in spotting hardware resource limits and depending on the limits being hit, there are different tuning paths.