ClusterLogSize Environment Variable is Non-default

[This topic is intended to address a specific issue called out by the Exchange Server Analyzer Tool. You should apply it only to systems that have had the Exchange Server Analyzer Tool run against them and are experiencing that specific issue. The Exchange Server Analyzer Tool, available as a free download, remotely collects configuration data from each server in the topology and automatically analyzes the data. The resulting report details important configuration issues, potential problems, and nondefault product settings. By following these recommendations, you can achieve better performance, scalability, reliability, and uptime. For more information about the tool or to download the latest versions, see "Microsoft Exchange Analyzers" at]  

Topic Last Modified: 2008-01-16

The Microsoft Exchange Server Analyzer Tool reads the following registry entry to determine whether the ClusterLogSize parameter has been set: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Session Manager\Environment\

If the Exchange Server Analyzer finds that the ClusterLogSize environment variable is set to a value other than the default value of 32 megabytes (MB) on a computer that is running Exchange Server 2007, the Exchange Analyzer displays a best practices message.

On a busy cluster, the cluster.log file wraps around so quickly that entries may be lost when you troubleshoot failover situations if the following conditions are true:

  • Troubleshooting requires a detailed review of the cluster log file.

  • The cluster is managing many resources.

Therefore, when troubleshooting requires use of the cluster.log file, increase the size to at least the default value of 32 megabytes (MB).


This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore the registry if a problem occurs. For information about how to restore the registry, view the "Restore the Registry" Help topic in Regedit.exe or Regedt32.exe.

To modify the default size of the cluster.log file

  1. Open a registry editor, such as Regedit.exe or Regedt32.exe.

  2. Navigate to: HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Environment.

  3. Right-click ClusterLogSize, and then click Modify.

  4. Modify the ClusterLogSize Value data to the new log file size. For example, modify the ClusterLogSize value to 32 and then press ENTER.

  5. Quit Registry Editor.

Before you edit the registry, and for information about how to edit the registry, see Microsoft Knowledge Base article 256986, "Windows registry information for advanced users" (

For more information about cluster logging in Microsoft Cluster Server, see Microsoft Knowledge Base article 168801, "How to Turn on Cluster Logging in Microsoft Cluster Server" (