Microsoft KB Archive/298879

= Exchange Server 2007, Exchange Server 2003, and Exchange 2000 Server may experience performance problems when the PDC emulator is used for DSAccess =

Article ID: 298879

Article Last Modified on 10/25/2007

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APPLIES TO


 * Microsoft Exchange Server 2003 Enterprise Edition
 * Microsoft Exchange Server 2003 Standard Edition
 * Microsoft Exchange 2000 Server Standard Edition
 * Microsoft Exchange Server 2007 Enterprise Edition
 * Microsoft Exchange Server 2007 Standard Edition

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This article was previously published under Q298879



Important This article contains information about how to modify the registry. Make sure that you back up the registry before you modify it. Make sure that you know how to restore the registry if a problem occurs. For more information about how to back up, restore, and modify the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows registry



SYMPTOMS
By default, DSAccess chooses the primary domain controller (PDC) emulator operations master role computer to handle requests in Microsoft Exchange. This action may result in poor performance if other non-Exchange programs are making heavy use of the PDC emulator.



RESOLUTION
To resolve this problem, add the MinUserDC registry value to exclude the PDC emulator from the server list that Exchange can use.

Note For Exchange Server 2007, we recommend that you use a cmdlet to configure the DSAccess component to exclude a particular domain controller or a list of domain controllers from use. For more information about how to do this, see the &quot;More Information&quot; section.

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

To add the MinUserDC registry value:  Start Registry Editor (Regedt32.exe). Locate and click the following key in the registry:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeDSAccess\Profiles\Default

Note In Exchange Server 2007, locate the  subkey instead of the   subkey. On the Edit menu, click Add Value, and then add the following registry value:

Value name: MinUserDC

Data type: REG_DWORD

Value data:  

Note The MinUserDC value determines how many total user domain controllers must be available for PDC emulator exclusion to turn on. 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 four domain controllers are available. When this condition is met, the PDC emulator is excluded from use, and DSAccess communicates only with the remaining three domain controllers.

 Exit Registry Editor.

Notes
 * You have to apply the registry change that this article describes regardless of the service pack that is installed.
 * In Exchange Server 2007, Exchange Server 2003, and Exchange 2000 Server Enterprise Edition, the  key and the   key are unavailable. You must create these keys in Exchange Server 2003 and in Exchange 2000 Server Enterprise Edition.
 * When you determine a value for MinUserDC, consider the equation n - 1, where n is equal to the total number of domain controllers in the site. This number includes the PDC emulator. Subtract 1 from this number, and the sum should be the value that you enter for MinUserDC.



STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the &quot;Applies to&quot; section.



MORE INFORMATION
In Exchange Server 2007, you can use a cmdlet to configure the DSAccess component to exclude a particular domain controller or a list of domain controllers from use. To do this, use the Set-ExchangeServer command together with the StaticExcludedDomainControllers option.

For more information about the Set-ExchangeServer command, visit the following Microsoft Web site:

http://technet.microsoft.com/en-us/library/8e8d3fca-59b3-4355-a637-28bf5e5ca4cf.aspx

Example
The following example illustrates how to use the Set-ExchangeServer command to exclude one or more domain controllers from use. Additionally, this example describes how to verify the status of the Exchange environment after you run the Set-ExchangeServer command.

The following table describes the servers that this example uses.

To use the Set-ExchangeServer command to exclude the three domain controllers that are listed in this table from use for the DSAccess component, follow these steps:  Start the Exchange Management Shell. To do this, click Start, point to All Programs, point to Microsoft Exchange Server 2007, and then click Exchange Management Shell.</li> At the command prompt, type the following command, and then press ENTER:

Set-ExchangeServer -identity E2K7-1.contoso.com -StaticExcludedDomainControllers:dc-1.contoso.com,dc-2.contoso.com,dc-3.contoso.com

This command excludes DC-1, DC-2, and DC-2 from use by the server that is named E2K7-1.

Note In this command, specify the fully qualified domain names of the individual domain controllers by using a comma-separated list that does not contain spaces between each entry.</li> To verify the list of excluded domain controllers, type the following command, and then press ENTER:

Get-ExchangeServer -identity E2K7-1.contoso.com -status | fl Name, StaticExcludedDomainControllers

</li></ol>

Note If you want to remove the changes that you have made, and revert to the default behavior of Exchange, type the following command at the Exchange Management Shell prompt, and then press ENTER:

Set-ExchangeServer -identity E2K7-1.contoso.com -StaticExcludedDomainControllers:$null

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