have 10 nodes in a replication set iwth only 1 primary. have node 11 on standby (ready to add to set) allowChaining must be true perform large update on primary followed immediately by updating replication set config to add node 11. some secondaries that sync to other secondaries will fail with "Restarting oplog query due to error: ExceededTimeLimit: Operation timed out, request was RemoteCommand..." the longer the chain of secondary->secondary->secondary...->primary the more likely sync will hang.