A setup of 2 shards (rs2 and rs1), each shard is a replicaset of 2 members primary and secondary, and an arbiter. Let's move a chunk from rs2 to rs1. In replicaset rs2, take the secondary member down. This is the balancer configuration in the config db: mongos> db.settings.find({_id: "balancer" }) { "_id" : "balancer" , "stopped" : true , "_secondaryThrottle" : false , "mode" : "off" } Run the moveChunk command: mongos> db.runCommand({moveChunk: "agent.pageloadHarEntries" , bounds:[{ _id: "a23036:108:1483038000:1483038060" },{ _id: "a23036:108:1483801200:1483801260" }], to: "rs1" , _secondaryThrottle: false }) { "code" : 96, "ok" : 0, "errmsg" : "moveChunk command failed on source shard. :: caused by :: WriteConcernFailed: waiting for replication timed out" } The logs in the primary member of rs2 shows tons of _transferMods commands until the migration is aborted with _recvChunkAbort. Attached you can find the logs of each primary. More info: I tried changing the _secondaryThrottle to true with writeConcern 1 so it only waits for the primary, but the same happens. If i start the secondary member, and repeat the moveChunk, it works. With the secondary member down, if i move the chunk the other way around, from rs1 to rs2, it works. Important: we had a small outage, caused by this because it probably entered in the critical section described here https://github.com/mongodb/mongo/wiki/Sharding-Internals#migration-protocol-summary