MongoDB Documentation, Release 3.0.4 If you run rs.syncFrom() during initial sync, MongoDB produces no error messages, but the sync target will not change until after the initial sync operation. Persistence replSetSyncFrom and rs.syncFrom() provide a temporary override of default behavior. mongod will revert to the default sync behavior in the following situations: Changed in version 2.4: The sync target falls more than 30 seconds behind another member of the replica set; the mongod will revert to the default sync target. Target The member to sync from must be a valid source for data in the set. To sync from a member, the member must: If you attempt to replicate from a member that is more than 10 seconds behind the current member, mongod will log a warning but will still replicate from the lagging member. If you run replSetSyncFrom during initial sync, MongoDB produces no error messages, but the sync target will not change until after the initial sync operation. To use the replSetSyncFrom command in the mongo shell: To use the rs.syncFrom() helper in the mongo shell: This section describes common strategies for troubleshooting replica set deployments. To display the current state of the replica set and current state of each member, run the rs.status() method in a mongo shell connected to the replica set’s primary . For descriptions of the information displayed by rs.status() , see http://docs.mongodb.org/manual/reference/command/replSetGetStatus . Note: The rs.status() method is a wrapper that runs the replSetGetStatus database command. Chapter 9. Replication 646 Check Replica Set Status 9.3.4 Troubleshoot Replica Sets Procedure db.adminCommand( { replSetSyncFrom: "hostname<:port>" } ); rs.syncFrom("hostname<:port>"); • The mongod instance restarts. • The connection between the mongod and the sync target closes. • Have data. It cannot be an arbiter, in startup or recovering mode, and must be able to answer data queries. • Be accessible. • Be a member of the same set in the replica set configuration. • Build indexes with the buildIndexes setting. • A different member of the set, to prevent syncing from itself.