Add Synchronous Replication

After you have promoted the backup group leader to group leader, you can set up synchronous replication on it.

NOTE: Make sure the upstream and downstream replication partners share a common snapshot.

Make sure the arrays are in-sync by entering the group --status command.

When the arrays are in-sync, you can modify the volume collection and configure synchronous replication.
Set the upstream volume to offline:

The steps to remove synchronous replication (see ) disassociate the downstream volume, which allows it to become available to host. However, the upstream volume remains unavailable.

When the arrays are in-sync again, you can move the upstream volume to offline by entering the following command:
```
NimbleOS $ vol --offline <volume_name> --pool <pool_name>
```
Remove upstream volume from the volume collection by entering the following command:
```
NimbleOS $ vol --dissoc <volume_name> --pool <pool_name>
```

Set up synchronous replication between the two replication partners by entering the following commands to edit the schedule and set the replication direction:

NimbleOS $ volcoll --editsched <volume_collection_name> --schedule Minimum 
--num_retain_replica <number_of_replicas> --retain <number_retained> 
--repeat <number_repetions> --repeat_unit <time_value> 
--replicate_to <downstream_pool_partner>

Associate the volume back to the volume collection. by entering the following command:

NimbleOS $ vol --assoc <volume_name> --volcoll 
<volume_collection_name> --pool <pool_name>

Confirm that the replication partners are in-sync by entering the following command:
```
NimbleOS $ volcoll --info <volume_collection_name>
```
Check the values for Synchronous Replication State and Synchronous Replication Last. They should be in_sync and now respectively:
```
Synchronous Replication State: in_sync    
Synchronous Replication Last In Sync: now  
```

You should perform a handover operation to return the original replication direction. For information about handovers, see Handover Overview. For the steps to perform a handover, see Perform a Handover.