The Mirroring - State alarm is raised when the mirror database is not synchronized or is synchronizing.
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Mirroring alarms are disabled by default. It is important to configure alarm thresholds that are appropriate to your environment before enabling these alarms.

Use a Spotlight Client to Configure | Alarms. You can configure this alarm to ignore certain values. You can configure different alarm severities for specific mirror databases. The key for this alarm is the name of the mirror database.