John, The default mode is the slowest of the 3 WAL write modes available. The other two are OS buffered write "LOG_ONLY" and Ignite buffered write "BACKGROUND".
You might need some benchmarking in your real environment (hardware and software) with your specific task to understand if it is "slow". Often you can significantly speed the things up with native persistence performance tuning like adjusting page size, using separate disk for WAL, SSD over-provisioning, etc. Please read about some tricks here <https://apacheignite.readme.io/docs/durable-memory-tuning#section-native-persistence-related-tuning> .
