Microsoft has dedicated resources for hosting services using IIS, but these recommendations may apply to any organization running larger numbers of websites on its servers. IIS 8.0 has been tested with thousands of websites per server and scales out well, assuming that adequate hardware resources are available. In general, most hosting companies have a target percentage of sites that will receive requests at any point in time. Microsoft assumes a 90 percent idle factor. This means that only 10 percent of sites will be receiving requests during normal operations. You will probably want to monitor your site activity to balance the ratio for your specific circumstances.
Hosting operations have normally developed a strategy for managing application pools, account access, storage locations, and management environments, but if you are looking for a starting point, Microsoft recommends the following:
This means that you will have at least three pieces of equipment: