Explanation/Reference:
Explanation:
To determine how many Exchange servers are required to manage user load, use the following capacity planning tools:
Microsoft Exchange Jetstress

Microsoft Exchange Load Generator

Note:
The Jetstress tool is designed to simulate Exchange I/O at the database level by interacting directly with the database technology of the Extensible Storage Engine (ESE), also known as Jet, that Exchange is built on. Jetstress can be configured to test the maximum I/O throughput available to your disk subsystem within the required performance constraints of Exchange, or it can accept a desired profile of user count and I/Os per second per user and validate that the disk subsystem is capable of maintaining an acceptable level of performance with such a profile. Jetstress testing can be used to validate storage reliability and performance prior to the deployment of Exchange servers. You should run Jetstress if you are concerned about your storage subsystem performance or if you need to determine a system's I/O capacity.
The Load Generator (LoadGen) tool is designed to produce a simulated client workload against a test Exchange deployment. This workload can be used to evaluate how Exchange performs, and can also be used to analyze the effect of various configuration changes on Exchange behavior and performance while the system is under load
Use the output from these tests in the following ways:
Validate deployments

Calculate the client computer response time for the server configuration under client load

Estimate the number of users per server

Identify bottlenecks on the server

References: https://technet.microsoft.com/en-us/library/dd335108(v=exchg.141).aspx