XADM: LoadSim, Microsoft Exchange Server Load Simulation Tool

• Microsoft Exchange Server, version 4.0

SUMMARY

This article describes what the Microsoft Exchange Server Load Simulation Tool, LoadSim.exe, was designed to do and what it's software and hardware requirements are. For more information, please see the documentation on the Microsoft Exchange Server CD, Support\LoadSim\LoadSim.doc, and the MS Exchange Performance: Concurrent Users Per Server whitepaper available on the Microsoft TechNet CD.

MORE INFORMATION

As a performance tool, LoadSim is primarily used to help answer the question: How many users per server does a Microsoft Exchange Server Support? This tool can be used to generate a graph of perceived client response time as a function of the number of active users.

LoadSim was designed to provide a realistic load on a Microsoft Exchange Server by simulating the behavior of multiple Microsoft Exchange clients. LoadSim takes advantage of the multithreading, multiprocessing, and shared memory features in Windows NT to create and manage up to several hundred simulated users on a single client computer. However, if you want to run a large test (several hundred users or more), you'll need multiple LoadSim client computers.

Tests

You can use LoadSim to specify and run three kinds of tests:

   1. User Initialization, creates folders and messages in user mailboxes.
   2. Public Folder Initialization, sets up the Public Folder hierarchy.
   3. Load Simulation, simulates multiple users performing a wide variety
      of client actions including, reading mail, sending mail, Schedule+
      actions, and use of Public Folders. This test can be set to simulate
      low, medium, and heavy client usage.

You can specify many different test configuration options in LoadSim to simulate the type of activity you expect to see in production and you can save each configuration to a separate .SIM file. This allows you to run a particular configuration multiple times and to use LoadSim in automated mode from the command-line.

Software Requirements

LoadSim should be run on Windows NT 3.51 or later. For demonstration purposes, you can run LoadSim on Windows 95. However, if you are going to run large tests, gather performance timing results, or perform directory import, you need to use Windows NT. In addition, you must have a Microsoft Exchange client installed on the computer running LoadSim.

Hardware Requirements

If you use LoadSim for performance analysis, you need to make sure that your client hardware won't adversely affect performance results. The response times reported by LoadSim for user actions should be based primarily on server load, not client hardware bottlenecks. To gather accurate performance timing data, your client computer should have at least 32 Mb of physical RAM. The number of simulated clients that can be reasonably supported on one physical computer will vary with the nature of users chosen. If, for example, you use the Medium default user setting, a 32 Mb client computer should support 100 simulated users with little or no degradation in client response time.

There are several limiting factors that affect the capability of a particular computer to support a particular type and number of LoadSim users, the effects of these factors vary depending on your topology, your hardware, and your user definitions; Some important considerations are:

1. Network bandwidth. One of the differences between 100 real users and 100 LoadSim users is that you can run all 100 LoadSim users on one computer. You should make sure the network hardware on your client computer(s) can handle the number of users per computer that you want to simulate.

2. Memory and pagefile size. Each LoadSim process, and, to a lesser degree, each thread in each LoadSim process uses some amount of system memory on its client computer, both in physical RAM and virtual memory. You can use the Windows NT Performance Monitor to make sure that your LoadSim users aren't using too much system memory or causing excessive pagefile activity on your client computer(s).

3. Disk I/O capacity. Some LoadSim user actions require disk access on the client computer. You should verify that your LoadSim users aren't exceeding the capacity of the I/O subsystem on each client computer.