XCON: Low MDB USERS Registry Entry Causes Slow Connector Performance (176076)

IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedit32.exe.

SYMPTOMS

Abnormally slow performance on an Exchange Server computer that has multiple connectors. You may see this problem in an organization with a large directory. To verify this, check the value for the Performance Monitor on Object = MSExchangeDS, Counter = ExDS Reads/sec. You should not see a result much greater than 10.

CAUSE

When a server's function is designated to be a Multiserver or a Connector/Directory Import server, it should be configured take into account the number of users in the organization, though it does not, itself, host these users. Currently, the Exchange Server Optimization Wizard, which is used to designate the function of the server in the Type of Server option, does not do this and assigns a default value of 25 for the number of users. This value is registered in the Windows NT registry at the location HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeMTA \Parameters as MDB Users.

Microsoft has confirmed this to be a problem in Exchange Server 5.0 for Windows NT.

WORKAROUND

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys and Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it.

If you have verified that the server's ExDS Reads/sec is greater than 10, increase the registry setting HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeMTA \Parameters\MDB USERS to 25 percent of the total number of users in the organization (not to exceed five thousand).