You cannot used named write concerns (eg: MAJORITY, W1, ACKNOWLEDGED) - as you must set the w value as per: https://www.mongodb.com/docs/manual/reference/write-concern/ 1. What would you like to communicate to the user about this feature? "majority": Requests acknowledgment that write operations have propagated to the calculated majority of the data-bearing voting members (i.e. primary and secondaries with members [n] .votes greater than 0). <number> : Requests acknowledgment that the write operation has propagated to the specified number of mongod instances. <custom write concern name> Requests acknowledgment that the write operations have propagated to tagged members that satisfy the custom write concern defined in settings.getLastErrorModes