Topic Last Modified: 2007-01-09
The Microsoft® Exchange Server Analyzer Tool queries the Exchange_DSAccess Microsoft Windows® Management Instrumentation (WMI) class in the root\MicrosoftExchangeV2 namespace to determine the number of global catalog servers present in the topology. The number of global catalog servers is determined by counting the number of entries for the DSAccessNameGC WMI key. If the Exchange Server Analyzer finds that only one global catalog server exists in the topology, the Exchange Server Analyzer displays a best practice recommendation.
For fault tolerance, it is a best practice to have at least two global catalog servers available to service Exchange Servers and users. A single global catalog server represents a single point of failure. Exchange 2000 Server, Exchange Server 2003, and Exchange Server 2007 depend on global catalog servers for a variety of functions. If a global catalog server is not available, mail delivery can become slow or stop completely. Also, if a global catalog server is not available, Exchange Server services may not start. If Exchange Server services do not start, users cannot access their mailboxes.
For scalability and for fault tolerance, it is recommended that you configure at least two global catalog servers in each Active Directory® directory service site. If a site spans multiple domains, it is recommended that you configure a global catalog for each domain where Exchange 2000 Server computers, Exchange Server 2003 computers, or Exchange Server 2007 computers and clients reside. Also, it is recommended that you deploy one global catalog server for every four Exchange Server computer processors.
For details about how to create additional global catalog servers, see the Microsoft Knowledge Base article 313994, "How To Create or Move a Global Catalog in Windows 2000" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=313994).
For more information about global catalog server placement and availability as it relates to Exchange Server, see the following Knowledge Base articles:
- 875427, "Global catalog server placement and ratios in an
Exchange 2000 Server organization or in an Exchange
Server 2003 organization" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=875427)
- 322801, "Exchange System Attendant Does Not Start, and You
Receive a 'Global Catalog Servers Not Responding' Error Message"
- 829361, "Exchange Server 2003 Computer Takes Longer Than
You Expect to Shut Down" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=829361)
- 304403, "Exchange Considerations for Promoting a Domain
Controller to a Global Catalog Server" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=304403)
- 305065, "Exchange Server-Related Considerations for Demoting a
Global Catalog Server to a Domain Controller" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=305065)