No. If you don't call fsync(), there's no guarantee that your data will _ever_ be written to disk. Some file systems with some settings may write data to hardw

No. If you don't call fsync(), there's no guarantee that your data will _ever_ be written to disk. Some file systems with some settings may write data to hardware after some delay or periodically, but others may not. fsync() "performs" e.g. an ATA FLUSH command on the underlying hardware.