All the drivers default to FSYNC_SAFE? Maybe the Java one didn't get the memo. It's set to ACKNOWLEDGED by default. https://github.com/mongodb/mongo-java-drive

All the drivers default to FSYNC_SAFE? Maybe the Java one didn't get the memo. It's set to ACKNOWLEDGED by default. https://github.com/mongodb/mongo-java-driver/blob/master/src/main/com/mongodb/MongoClientOptions.java#L56 https://github.com/mongodb/mongo-java-driver/blob/master/src... I like Mongo. And until I really learned about it, I got bitten by the default a few times. Personally I use REPLICA_ACKNOWLEDGED when running in a cluster and FSYNC when writing to a single node.