Compaq ProLiant 6000 Software Manual page 5

ECG052.0897
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(cont.)
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For example, in any system there will be bursts of activity due to coincidence, when more users
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than usual initiate actions at nearly the same time. These bursts can be random in nature or a
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consequence of scheduled events that affect many users on the same server, such as when a large
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meeting adjourns. Additionally, the near-real-time notification mechanisms built into Microsoft
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Exchange Server may contribute to the quantum effect. Users on the same server are notified that
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a new message has arrived at essentially the same time. If the message was sent to a large number
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of users, a burst of activity may occur as many of those users read the message immediately upon
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. . receipt.
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Fortunately, the quantum effect becomes less and less significant as the number of users hosted
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per server increases. Because of the large number of users Microsoft Exchange Server can
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typically host, even on small servers, only the largest variations in user activity are typically
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noticeable by the server. From the user's perspective, however, the quantum effect is still
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noticeable if the server is under load. The sudden increase in server load affects the delay between
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the initiation of an action by the user and the server's response to it.
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LoadSim
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. . The main tool used in generating the performance data contained in this paper was the Microsoft
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Exchange Server User Load Simulation utility called LoadSim. As its name implies, LoadSim is a
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tool for simulating a client user load on an Exchange Server. Its purpose is to enable a single
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Windows NT machine—called a LoadSim client—to simulate multiple Microsoft Exchange client
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users. The current version of LoadSim not only provides simulation of MAPI protocol clients but
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also provides support for POP3, NNTP, LDAP, and HTTP client protocols.
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The operation of LoadSim users is governed by a LoadSim profile. This profile controls factors
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. . such as how long a LoadSim 'day' is, how many email messages to send in a day's time, how
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many times to open and read existing email, whether to use distribution lists, whether to use
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public folders, etc.
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LoadSim is a simulator and therefore not a perfect image of real-world activity. Because of the
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nature of the product and the quantum effect discussed previously, it is impossible to fully emulate
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a client. Thus there are two points to remember when considering this data: First, the LoadSim
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results do not properly address users' logging on and off. When a test is run, all users log on
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sequentially. Once this process is complete, users begin their tasks. If users typically log on and
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off multiple times during the day, the NT logon can have an impact on server and network rates
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. . of utilization, especially when many users log on simultaneously. Based on your organization's
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implementation, these factors could pose important considerations in addition to those presented
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in this paper. The second point to remember is that the response numbers generated by LoadSim
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are based on server response to clients and do not account for strictly client-side actions such as
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rendering rich text once a message is received.
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LoadSim, despite possible shortcomings, creates a highly accurate simulation of reality. It mimics
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the full Microsoft Exchange Client in many respects. First, it uses .MSG files, the same format
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. . used by the Exchange Client. This guarantees that messages generated by LoadSim have the same
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properties as those sent by real users of the Exchange Client. Second, LoadSim uses the same
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remote procedure call (RPC) semantics as those used by the Client. Third, LoadSim registers
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MAPI change notifications in the same manner as they are registered by the Client. Finally,
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LoadSim even emulates the Microsoft Exchange Client list-box cache, which the Client uses for
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folder and message panes in the viewer when a user browses and selects messages on the server.
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