As your directory evolves, the service levels that must be supported might change. To raise the level of service after a system has been deployed can be difficult. Thus, the initial design must take future requirements into account.
When defining scalability requirements, consider the following:
Is there an anticipated increase in entry volume?
How many new users are expected within the next few years?
What is the expected growth rate, over the next few years, in terms of data, users, and client applications?
Are any new business processes expected?
Increase CPU estimates to make sure that your deployment does not have to be scaled prematurely. Look at the anticipated milestones for scaling and projected load increase over time to make sure that you allow enough latent capacity to reach the milestones.