kubernetes/vendor/go.etcd.io/etcd/client/pkg/v3/fileutil/sync_darwin.go

// Fsync on HFS/OSX flushes the data on to the physical drive but the drive
// may not write it to the persistent media for quite sometime and it may be
// written in out-of-order sequence. Using F_FULLFSYNC ensures that the
// physical drive's buffer will also get flushed to the media.
func Fsync(f *os.File) error { … }

// Fdatasync on darwin platform invokes fcntl(F_FULLFSYNC) for actual persistence
// on physical drive media.
func Fdatasync(f *os.File) error { … }