Exchange Server Sizing and Tuning


Topic Last Modified: 2006-08-16

To determine the number of Exchange servers you need to handle user load, use the following capacity planning tools:

  • Microsoft Exchange Server Load Simulation Tool (LoadSim.exe)

  • Exchange Stress and Performance (ESP) tool

  • Jetstress

Because some of these tools create accounts that have insecure passwords, these tools are intended for use in test environments, not in production environments.

With Microsoft Exchange LoadSim, you can simulate the load of MAPI clients against Exchange. You simulate the load by running LoadSim tests on client computers. These tests send messaging requests to the Exchange server, causing a load on the server.

Use the output from these tests in the following ways:

  • To calculate the client computer response time for the server configuration under client load

  • To estimate the number of users per server

  • To identify bottlenecks on the server

For more information about the LoadSim tool or to download LoadSim, see Exchange 2003: Load Simulator 2003 (LoadSim) (

The Exchange Stress and Performance tool (ESP) is a highly scalable stress and performance tool for Exchange. It simulates large numbers of client sessions by concurrently accessing one or more protocol services. Scripts control the actions each simulated user takes. The scripts contain the logic for communicating with the server. Test modules (DLLs) then run these scripts. Test modules connect to a server through Internet protocols, calls to application programming interfaces (APIs), or through interfaces like OLE DB.

ESP is modular and extensible and currently provides modules for most Internet protocols, including the following:

  • Web Distributed Authoring and Versioning (WebDAV)

  • Internet Message Access Protocol version 4rev1 (IMAP4)

  • Lightweight Directory Access Protocol (LDAP)

  • OLE DB

  • Post Office Protocol version 3 (POP3)

  • Simple Mail Transfer Protocol (SMTP)

For more information about the ESP tool or to download ESP, see the Microsoft Exchange 2003 Tools and Updates Web site (

Exchange 2003 is a disk-intensive application that requires a fast, reliable disk subsystem to function correctly. Jetstress (Jetstress.exe) is a tool in Exchange to help administrators verify the performance and stability of the disk subsystem prior to putting their Exchange server into production. For more information about Jetstress, see "Exchange Server 2003 Jetstress Tool" (

A server's virtual address space usage determines a mailbox server's overall performance and scalability. When virtual memory runs low, performance decreases dramatically. Although Exchange 2003 automatically optimizes usage for small- to medium-sized servers, additional tuning is necessary for servers with more than 1 GB of physical memory.

For more information about monitoring and optimizing memory usage on your servers, see Optimizing Memory Usage for Exchange Server 2003.