Exchange Load Generator Debuts - 26 Feb 2007

With the advent of Exchange Server 2007, Microsoft decided to rebuild Microsoft Exchange Load Simulator (LoadSim). LoadSim simulates the work done by users running Outlook to measure the performance of a given hardware configuration and discover how many concurrent users it can support. In the rebuilding, one goal was to build a more accurate load generator that would more faithfully replicate the way Outlook 2007 and Outlook 2003 perform Messaging API (MAPI) operations. Another was to provide better reporting and a larger set of adjustable parameters so that testers could have more granular control over their test setup and behavior. The result of these efforts is the Exchange Load Generator (LoadGen).

LoadGen is designed to closely mimic the behavior of Outlook clients running on Exchange 2007 servers. It shares some operating similarities with LoadSim. For example, you can specify two timing parameters: how long to run the test and how long a simulated workday is. The workday interval controls how often client tasks are dispatched. There are tons of other adjustable parameters: You can control what percentage of messages should trigger common actions such as replies, deletions, or moves; you can specify how deeply folders should be nested; you can decide how many messages should be kept in mailboxes; and much more.

However, LoadGen differs significantly from LoadSim. My favorite new feature is stress mode. As you might expect, this feature’s job is to stress the target server by dispatching tasks to it as quickly as possible, ignoring the workday length parameter. For a recent set of benchmark tests, I set up a stress run with 300 mailboxes that quickly smoked out a serious performance problem with the target system by slamming it with 300 users’ worth of heavy mailbox usage. (You can configure multiple profiles with different levels of activity.) LoadGen is much more efficient at generating load; a single dual-processor server can easily simulate several thousand users (but if you set the concurrency percentage too high you won’t get the full benefit). You can use a single LoadGen instance to control load generation on multiple machines at the same time. The new LoadGen tool comes, interestingly, in both 32- and 64-bit versions, so you can use a 32-bit server or a 64-bit server to generate load against your 64-bit Exchange hardware.

With the advent of Exchange Server 2007, Microsoft decided to rebuild Microsoft Exchange Load Simulator (LoadSim). LoadSim simulates the work done by users running Outlook to measure the performance of a given hardware configuration and discover how many concurrent users it can support. In the rebuilding, one goal was to build a more accurate load generator that would more faithfully replicate the way Outlook 2007 and Outlook 2003 perform Messaging API (MAPI) operations. Another was to provide better reporting and a larger set of adjustable parameters so that testers could have more granular control over their test setup and behavior. The result of these efforts is the Exchange Load Generator (LoadGen).

LoadGen is designed to closely mimic the behavior of Outlook clients running on Exchange 2007 servers. It shares some operating similarities with LoadSim. For example, you can specify two timing parameters: how long to run the test and how long a simulated workday is. The workday interval controls how often client tasks are dispatched. There are tons of other adjustable parameters: You can control what percentage of messages should trigger common actions such as replies, deletions, or moves; you can specify how deeply folders should be nested; you can decide how many messages should be kept in mailboxes; and much more.

However, LoadGen differs significantly from LoadSim. My favorite new feature is stress mode. As you might expect, this feature’s job is to stress the target server by dispatching tasks to it as quickly as possible, ignoring the workday length parameter. For a recent set of benchmark tests, I set up a stress run with 300 mailboxes that quickly smoked out a serious performance problem with the target system by slamming it with 300 users’ worth of heavy mailbox usage. (You can configure multiple profiles with different levels of activity.) LoadGen is much more efficient at generating load; a single dual-processor server can easily simulate several thousand users (but if you set the concurrency percentage too high you won’t get the full benefit). You can use a single LoadGen instance to control load generation on multiple machines at the same time. The new LoadGen tool comes, interestingly, in both 32- and 64-bit versions, so you can use a 32-bit server or a 64-bit server to generate load against your 64-bit Exchange hardware.