How to Set the MinUserDC Registry Value
A primary domain controller (PDC) emulator is an Active Directory operations master role computer that processes replication requests from Microsoft® Windows NT® 4.0 backup domain controllers and processes all password updates for clients that are not running Active Directory–enabled client software. PDC emulators are also domain controllers, and are therefore available for use by applications such as Exchange.
Directory Service Access (DSAccess) is an internal component in Exchange 2000 Server and Exchange Server 2003 that controls how all Exchange components access Active Directory. The primary function of DSAccess is to maintain information about various directory-related events and operations. For example, DSAccess discovers the Active Directory topology and detects if domain controllers and global catalog servers are available and responding to queries.
By default, DSAccess includes the PDC emulator computer in its list of available and usable domain controllers. If non-Exchange programs are making heavy use of the PDC emulator, using the PDC emulator by DSAccess could cause performance problems on the PDC emulator computer, as well as on the Exchange server and the non-Exchange program computer.
To prevent such performance issues, the MinUserDC registry value can be added to the registry on an Exchange server to force DSAccess to query all other available domain controllers before querying the domain controller that holds the PDC emulator operations master role.
Before You Begin
Before you perform the procedure in this topic, be aware that the procedure contains information about editing the registry.
Warning
Incorrectly editing the registry can cause serious problems that may require you to reinstall your operating system. Problems resulting from editing the registry incorrectly may not be able to be resolved. Before editing the registry, back up any valuable data.
Procedure
To set the MinUserDC registry value
Open a registry editor, such as Regedit.exe or Regedt32.exe.
Navigate to HKLM\System\CurrentControlSet\Services\MSExchangeDSAccess\Profiles\Default
Locate the MinUserDC value and make any required changes. If this DWORD value does not exist, you can manually create it.
The value data that is configured for the MinUserDC registry entry is the maximum number of domain controllers to contact before contacting the PDC emulator. For example, setting MinUserDC to 4 configures DSAccess to exclude the PDC emulator only when a total of 4 domain controllers are available. When this condition is met, the PDC emulator is excluded from use and DSAccess communicates only with the remaining 3 domain controllers.
For More Information
For more information about using the MinUserDC registry entry, see Microsoft Knowledge Base article, 298879, "Exchange Server 2003 and Exchange 2000 Server may experience performance problems when the PDC emulator is used for DSAccess," (https://go.microsoft.com/fwlink/?linkid=3052&kbid=298879).
For information about how to edit the registry, see Microsoft Knowledge Base article 256986, "Description of the Microsoft Windows Registry" (https://go.microsoft.com/fwlink/?linkid=3052&kbid=256986).