MongoDB Documentation, Release 3.0.4 } } ] You could add tag sets to the members of this replica set with the following command sequence in the mongo shell: After this operation the output of rs.conf() would resemble the following: conf = rs.conf() conf.members[0].tags = { "dc": "east", "use": "production" } conf.members[1].tags = { "dc": "east", "use": "reporting" } conf.members[2].tags = { "use": "production" } rs.reconfig(conf) { "_id" : "rs0", "version" : 2, "members" : [ { "_id" : 0, "host" : "mongodb0.example.net:27017", "tags" : { "dc": "east", "use": "production" } }, { "_id" : 1, "host" : "mongodb1.example.net:27017", "tags" : { "dc": "east", "use": "reporting" } }, { "_id" : 2, "host" : "mongodb2.example.net:27017", "tags" : { "use": "production" } } ] } Important: In tag sets, all tag values must be strings. Given a five member replica set with members in two data centers: Create a custom write concern to require confirmation from two data centers using replica set tags, using the following sequence of operations in the mongo shell: Custom Multi-Datacenter Write Concerns 1. a facility VA tagged dc.va 2. a facility GTO tagged dc.gto 1. Create a replica set configuration JavaScript object conf : Chapter 9. Replication 636