What is Active Manager in Exchange Server ?

Microsoft Exchange Server includes a component called Active Manager, that manages the high availability platform, that includes the Database availability group (DAG) and mailbox database copies. It runs inside the Microsoft Exchange Replication service (MSExchangeRepl.exe) on all Mailbox servers.

Mailbox servers that aren't members of a DAG, there is a single Active Manager role: Standalone Active Manager.

Active Manager stores current mailbox database information (for example, active and passive data, and mounted data) in the cluster database (also known as the cluster registry). Although the information is stored directly in the cluster database, it isn't accessed directly by any other components.

Servers that are members of a DAG, there are two Active Manager Roles:

1) Primary Active Manager (PAM)
2) Standby Active Manager (SAM)

PAM

DAG member that holds the PAM role is always the member that currently owns the cluster quorum resource (default cluster group). If the server that owns the cluster quorum resource fails, the PAM role automatically moves to a surviving server that takes ownership of the cluster quorum resource. 

Below are the task taken care by the PAM:

• Decides which copies will be active and passive 
• Responsible for getting topology change notifications
• Reacting to server failures
• Controls all movement of the active designations between a database's copies
• Also performs the functions of the SAM role on the local system (detecting local database and local Information Store failures).

If you need to take the server that hosts the cluster quorum resource offline for maintenance or an upgrade, you must first move the PAM to another server in the DAG.

SAM

Provides information on which hosts the active copy of a mailbox database is to other components of Exchange Server that are running an Active Manager Client component (Exmp: CAS or Transport services).

Below are the task taken care by the SAM:

• Detects failures of local databases and the local Information Store
• Reacts to failures by asking the PAM to initiate a failover (if the database is replicated)
• SAM doesn't determine the target of failover
• It also does not update a database's location state in the PAM
• Access the active database copy location state to answer queries for the active copy of the database that it receives.