It doesn't seem you can lose data even when you might otherwise expect to ;) I setup a small replica set using mongod --fork --logpath a.log --smallfiles --oplogSize 50 --port 27001 --dbpath data/z1 --replSet z mongod --fork --logpath b.log --smallfiles --oplogSize 50 --port 27002 --dbpath data/z2 --replSet z mongod --fork --logpath c.log --smallfiles --oplogSize 50 --port 27003 --dbpath data/z3 --replSet z And initalized it: > rs.initiate( { _id:'z', members:[ { _id:1, host:'localhost:27001' }, { _id:2, host:'localhost:27002' }, { _id:3, host:'localhost:27003' } ] } ); Then I killed all three processes: kill -9 25542 25496 25483 Next I brought one of them back up mongod --fork --logpath c.log --smallfiles --oplogSize 50 --port 27003 --dbpath data/z3 and inserted a doc > db.foo.insert({a:1}) Then I killed that process kill -9 25885 and brought the replica set back online using mongod --for