When I worked at CNN.com (96-01), we never found a way that was even close to simulating what production traffic did to our web farm. Our most important number that we knew for our web servers was that tip over point.

We actually kept track of two things: the red line point, if you will – which at the time was about 20,000 hits per minute/server – and what a box could really do. Back before CNN had load balancers, we would put multiple IPs onto a box – load it up – to see what it could do. And we were very quick to move traffic to other boxes when a box started to fail.

Later when I moved to EarthLink, I was unpleasantly surprised to find out what the engineers did not know these numbers for the various servers. Knowing that number makes planning easier, and it makes justifying new purchases easier: “See this graph of our traffic? And see how it compares to our capacity?”