Topic Last Modified: 2005-12-15

The Microsoft® Exchange Server Analyzer Tool queries the Exchange_PublicFolder Microsoft Windows® Management Instrumentation (WMI) class under the root\MicrosoftExchangeV2 namespace to determine the number of entries in the ReplicaList key. The number of entries represents the number of free/busy replicas that are present in each administrative group.

The Exchange Server Analyzer also queries the Active Directory® directory service to determine the count of the entries listed in the homeMDBBL attribute of each mailbox store. The count of this attribute represents the number of mailboxes on the mailbox store.

If the Exchange Server Analyzer finds that only a single free/busy replica exists in an administrative group that contains more than 10,000 mailboxes, the Exchange Server Analyzer displays an error.

It is generally recommended that more than one replica of the free/busy folder exist in each administrative group. Sometimes multiple free/busy replicas can increase performance and resilience. In large Exchange organizations, a single replica of free/busy data may become overloaded. In all Exchange organizations, a single replica of the free/busy data is a single point of failure.

It is recommended that multiple replicas be used despite the following considerations:

At a minimum, there should be one replica for every 10,000 mailboxes.

For more information about free/busy folders and publishing free/busy information, see "Working with Exchange Server 2003 Stores" (