Monitoring Benefit
The Active Preference check reports whether active database copies are running on the servers you nominated to host them.
This matters more than it first appears. After a failover, Exchange does not move active copies back to their preferred servers on its own. The original fault gets fixed, everything reports healthy, and the environment quietly stays unbalanced — often with more active databases on one server than it was sized for. This check is what tells you that has happened.
How do we verify the monitoring test results?
1. See where the active copies actually are. From the Exchange Management Shell on one of the Exchange servers:
cd $exscripts
.\RedistributeActiveDatabases.ps1 -DagName "<your DAG name>" -ShowDatabaseCurrentActivesThe output shows which server currently hosts each active copy, and will align with what the monitoring page presents.
2. Decide whether it matters. A copy being off its preferred server is not a fault in itself — it means a failover happened and has not been reversed. The question is whether the current distribution leaves any server carrying more load than it should.
3. Rebalance when you are ready. The same script redistributes copies back to preference. Do it during a maintenance window: moving active databases briefly disconnects the clients using them.
Common warning or error results, and potential solutions
| Result | Potential solution |
| One or more databases not on their preferred server | Expected after a failover. Confirm the original cause has been resolved, then rebalance with RedistributeActiveDatabases.ps1 during a maintenance window. |
| Databases drift off preference repeatedly | Something is still causing failovers. Check Replication Health and the cluster and storage event logs on the servers losing their active copies — rebalancing alone will not stop it recurring. |
| Everything reports healthy but users report slowness | Check this indicator before anything else. A server hosting several times its intended number of active databases will perform poorly while reporting no errors at all. |
| Preference is set but appears to be ignored | Confirm the activation preference values on the database copies are what you expect. Preference is a property of each copy, and it can be changed without anyone noticing. |
| Results are stale rather than failing | If several unrelated checks stopped updating at the same moment, look at the ENow SQL database connection rather than at the DAG. |
Monitoring page. The detail behind this indicator is served by the ENow web server at:
http://localhost:20080/MailscapeWeb/DAG/DAGActivePreference.aspx?server=<SERVER>Replace localhost with the web server's host name if you are browsing from elsewhere, 20080 with your own port if it was changed at installation, and <SERVER> with the monitored server you are investigating.
See also. Exchange Server - Namespace DAG Status for an overview of all the DAG checks and how they relate.
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