The image maxav005.gif shows the LGWR SYNC operation.
The primary site contains an online redo log and the log writer (LGWR) process. The standby site contains a remote file server (RFS) and a standby redo log.
On the primary site, a write request arrives at LGWR, which sends it to the online redo log. The online redo log sends a reply back to LGWR. LGWR passes the reply back and also sends the write request to RFS on the standby site.
RFS sends the write request to the standby redo log, which sends a reply back to RFS. RFS sends the reply back to LGWR.
End of image description.