DSAccess tuning values in the Instance0 registry subkey are deleted when you configure Directory Access to automatically discover the configuration domain controller in Exchange 2000 Server

On your Microsoft Exchange 2000 Server, DSAccess cache tuning values that you manually configured in the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeDSAccess\Instance0 registry subkey no longer have any performance effect. When you try to view the registry subkey, you notice that the Instance0 subkey that held the tuning values no longer exists.

This problem occurs if you enable the Automatically discover servers option for Directory Access to automatically discover the configuration domain controller. When you enable the Automatically discover servers option for the configuration domain controller, the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeDSAccess\Instance0 registry subkey is unexpectedly deleted.

The ConfigDCHostName registry entry and the ConfigDCPortNumber registry entry in the Instance0 subkey are used to statically map the Configuration Domain Controller value. Instead of removing only the ConfigDCHostName and ConfigDCPortNumber registry entries as you expect, when the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeDSAccess\Instance0 registry subkey is deleted any manually entered DSAccess tuning values that you configured by using the Instance0 subkey are lost.

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, submit a request to Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.
The English version of this hotfix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.
Note Because of file dependencies, this update requires Exchange 2000 Server Service Pack 3 (SP3). For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

To work around this problem, back up the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeDSAccess\Instance0 subkey before you enable the Automatically discover servers option for Directory Access to automatically discover the configuration domain controller. After you enable the Automatically discover servers option, restore the registry subkey. To preserve the enabled Automatically discover servers setting, you must edit the registry file before you restore it. To do so, follow these steps.

Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

1. Start Registry Editor. To do so:
   1. Click Start, and then click Run.
   2. In the Open box, type regedit, and then click OK.
2. Locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeDSAccess\Instance0
3. On the Registry menu, click Export Registry File.
4. Type a file name in the File name box, and then click Save.
5. Right-click the registry file that you saved in step 4, and then click Edit.
6. Remove the "ConfigDCPortNumber"=value and the "ConfigDCHostName"="hostname" lines.
   
   Note This step preserves the Automatically discover servers setting when you enable the setting in step 7. If you do not delete these two lines, the Automatically discover servers option will be disabled when you restore the registry subkey.
7. Save the edited registry file.
8. After you enable the Automatically discover servers option for the configuration domain controller, double-click the registry file that you saved in step 4, and then click Yes to restore the information to the registry.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section of this article.

To locate the Automatically discover servers check box for the configuration domain controller, follow these steps:

1. In Exchange System Manager, expand Servers, right-click your Exchange 2000 server name, and then click Properties.
2. Click the Directory Access tab.
3. In the Show list, click Configuration Domain Controller. The Automatically discover servers check box appears at the bottom of the Directory Access tab.

For additional information about DSAccess, click the following article numbers to view the articles in the Microsoft Knowledge Base: For more information about DSAccess performance tuning, visit the following Microsoft Web site, and then click the Tuning Exchange 2000 Performance hyperlink: For additional information about the standard terminology that is used in Microsoft software updates, click the following article number to view the article in the Microsoft Knowledge Base: