As discussed previously, the replica is a copy of state data and code of your application. When you deploy a partitioned stateful service, replicas of each partition form a replica set. Each replica in a replica set takes one of the following roles:

1. Primary: This replica caters to all the write requests. A replica set can have only one primary replica. Whenever the state data is created or modified, the change is communicated to the secondary replicas that needs to be acknowledged by them. The primary replica waits for acknowledgements from a quorum of replicas to commit the change.
2. Active secondary: The replicas in active secondary participate in the write quorum. All participant active secondaries in the write quorum must acknowledge the change in state after committing the change to their own storage.
3. Idle secondary: The idle secondaries receive update from the primary but do not participate in the write quorum. In case an active secondary instance fails, an instance of idle secondary will be promoted to the status of active secondary.
4. None: A replica with this state does not hold any state. A replica that is being decommissioned holds this state.

You can view the replica states in Service Fabric Explorer by drilling down to the replica level.