building a high traffic web portal

i am building a web portal using codeigniter.
would like to know the traffic it can handle and which areas need to be improvised or taken care of.
also any hardware specs as i am expecting 1-10 million visitors after successful launch.
any lights or suggestions would be helpful .

TIA

The first thing you can do is run a Apache AB test on it.

http://httpd.apache.org/docs/2.2/programs/ab.html

Hit a few different urls and compare the results.

Secondly you want to look into a siege test

http://www.joedog.org/siege-home/

That thing can really put a hurting on your server(s).

Finally, remember PHP is a shared nothing language. You can always fire up another box and put a load balancers in front of them.

https://github.com/ProjectOrangeBox / https://github.com/dmyers2004