Group Metrics is a collection of the following data about distribution groups and dynamic distribution groups in Exchange 2010.
- Number of members in the group.
- Number of members who are external users.
This information is needed for the MailTips to display “large audience” and “external recipients” information when a user composes an email. “Large audience” MailTip is displayed when a sender adds a distribution group whose membership count is considered a large audience as configured in your organization. “External Recipients” MailTip is displayed when a sender adds a distribution group that has members who are external to your organization.
The question is how the group metrics work in Exchange 2010? By default, the mailbox server which is responsible for generating OAB generates the group metrics as well. It stores the information in a “.bin” file in Exchange ServerV14Client AccessGroup Metrics on the mailbox server.
The .bin file is the main group metrics data file. It contains the membership and external members count for all distribution groups and dynamic distribution groups in your organization. The XML file contains information about the mailbox server configured to generate the group metrics data. This file is required by the Exchange File Distribution service and it points to the binary file that needs to be distributed. ChangedGroups.txt file contains the list of groups that were updated the last time group metrics data was generated.
The Mailbox server generates full group metrics data for all distribution groups and dynamic distribution groups every sunday and incremental updates for any groups that were modified since the last full generation. The day of the full group metrics data generation is fixed, but you can configure the time it is generated daily. By default, group metrics data is generated daily at a random time within two hours of midnight.
Run the following command to change the time at which group metrics is generated.
Set-MailboxServer –Identity “servername” -GroupMetricsGenerationTime 01:00
The group metrics data that is generated on the designated mailbox servers (OAB generation server by default) is copied to Client Access servers using the Exchange File Distribution Service every 8 hours. The File Distribution service queries Active Directory for the list of mailbox servers that have group metrics generation enabled and then copies the group metrics data from the closest mailbox server. The process is similar to OAB generation and distribution.
Either restart the File Distribution service or run the command below if you want to force CAS server to copy the group metrics data.
Update-FileDistributionService –identity “servername” –type GM
If the “type” parameter is not used, all data for OAB, group metrics and UM are reloaded.
The copied files are placed in Exchange ServerV14Client AccessGroup Metrics on the CAS server, from which it is distributed to clients.
The entire process is similar to OAB generation and distribution, explained here.