For simplicity, the run shown in Screen 1 simulates only five LoadSim users. The fourth through eighth lines show LoadSim creating messaging profiles for those five users because they weren't already in the Registry. The next time you run LoadSim, this step won't be necessary.
The next five lines show the five LoadSim users successfully logging on to the Exchange server. This display shows up in every run so that you can see the users are logged on. As the users log on, LoadSim increments the number beside the Users field at the top of the screen.
In the final five lines, you see LoadSim user activity. Each line shows the activity detail for a LoadSim user. For example, in the last entry, you see the date and time of the activity, followed by the LoadSim user name and the activity detail. In this entry, at 23:28:41, user arrakis-exch2 browsed the Deleted Items folder for existing messages and found none.
This information tells me I need to run Initialize Database, which I'll cover in part three of the series. If the database is initialized properly, LoadSim won't find empty folders.
By default, LoadSim writes all this data to the loadsim.sum, loadsim.out, and loadsim.log log files. A utility that comes with LoadSim, LSLOG, lets you analyze the scores from a LoadSim log. LSLOG parses all the data that LoadSim collects and spits out the summarized results, which you can use for creating a users-per-server graph. I will cover details about LSLOG in part four of this series.
LoadSim User Profiles
LoadSim works with user profiles. User profiles determine how much load a simulated user places on Exchange Server. LoadSim comes with three default user profiles—Light, Medium, and Heavy—that represent three classes of users in LoadSim.
Table 1, page 166, lists the default LoadSim user profiles and their attributes. Don't let all the attributes and their associated values confuse you. If you don't know what an entry means, don't worry; the meaning will become evident later. You need each attribute to properly simulate an Exchange user. The Approximate Message Traffic values at the bottom of the table are based on the other values in the table. For example, if you increase the amount of new mail sent per day, the calculated numbers go up accordingly.
The three user profiles give you an idea of the different loads you can place on Exchange Server with LoadSim. More important, you can now analyze these user loads and determine which one best fits your organization.
The Heavy profile is most useful as a stress test rather than as a user test. It does not represent a realistic user profile, because the load is so intense. However, if you need to pound on your server to test its limits or to see whether software breaks, the Heavy profile is useful.
The Medium profile most closely reflects users who rely on email, such as a Fortune 500 corporate email user who depends on email as a regular, integral part of corporate communications. The Medium profile is a practical upper limit or worst-case scenario for estimating the number of users Exchange Server can support. In other words, if the Exchange server being tested can support 300 Medium users with acceptable client response time and server performance, you can plan to support approximately 300 real users on that server.
The Light profile most closely reflects users who employ email infrequently or irregularly. A good example is a user at a small company or at a company that has just started using email. The users do not rely heavily on email yet, so their usage pattern is light. Light represents a practical best-case scenario for many circumstances.
Of course, you aren't stuck with the three profiles LoadSim provides. The three profiles exist to get you started and to provide a common frame of reference for comparing sets of LoadSim data. You can configure LoadSim user profiles to mirror your particular users.
How Many Users Can I Simulate?
Your next question might be, "How many users can I simulate?" This question has two answers.
First, the limit to the total number of users you can simulate depends on the number of LoadSim clients you have and the number of users Exchange Server supports. You can, for example, simulate 20,000 users if you have enough LoadSim machines and a powerful enough Exchange Server.
Second, the number of users one LoadSim client can simulate depends on the class of hardware the client is running on and the profile you choose. Because you have to be running NT, you need to factor in that requirement. Table 2 shows some typical hardware recommendations for a LoadSim client. The estimates are conservative, but I don't recommend exceeding these numbers of simulated users per LoadSim client if you want to produce a valid user load on the Exchange Server computer.
Furthermore, when using MAPI, if you plan to rely on the score that a particular LoadSim client produces, do not simulate more than 100 users of any profile on that client. If you stay within the guidelines listed in Table 2, the user load you place on the server will be accurate.
If you attempt more users, however, your score will likely be skewed higher than it should be. The higher score will make Exchange Server appear as though it is performing worse than it really is. The result? Although the score on the LoadSim client might be inaccurate, the Exchange Server performance data remains valid. In fact, this approach is one way to squeeze more simulated users out of fewer machines. I'll cover this concept in detail in part four.
When you simulate a significantly higher number of LoadSim users—for example, 300 or more—on one client, the LoadSim client will eventually bottleneck. In this case, LoadSim will not produce the intended load on the Exchange Server computer. Both the LoadSim score and the Exchange Server performance data will be completely unusable.
What to Look for in a LoadSim Run?
Look for two items from a LoadSim run against Exchange Server: the load placed on Exchange Server and the response time (score) of the LoadSim client. The more complex item is observing the load on Exchange Server.
NT Performance Monitor (PerfMon) is the best tool to accomplish this task. Some PerfMon objects and counters are generic to NT and others are specific to Exchange Server. But all the counters together tell a large part of the story about how your server is faring under the load.
Of course, you don't have to run LoadSim to monitor PerfMon counters, which are also useful for observing a server under a real user load. Some preconfigured PerfMon workspaces are installed with Exchange Server. If you need to keep an eye on things, become familiar with the counters in these workspaces because they might be helpful.
The second task is to analyze the score on the LoadSim client. The score represents LoadSim's main performance metric. The score simply represents the average LoadSim client response time in milliseconds. I'll cover this issue in part four of the series.
I've introduced LoadSim and how you can use it to simulate the load on an Exchange Server. In part two, I'll review the basic steps to configure LoadSim. In part three, I'll describe customizing the LoadSim parameters. In the fourth installment, I'll explain initializing the Exchange database, running the test, and collecting and analyzing the data.