Most Oracle installations do not maintain the default redo log file
organization because it becomes a single point of failure. If one of your redo log files becomes corrupted, the system stops working. To address this problem, Oracle provides you with a way to multiplex redo log files.
Multiplexed redo log files
The following diagram explains multiplex redo log files.
Let us take the above example and add a new redo log group. There are two init.ora parameters that you should be aware of. First, you need to make sure MAXLOGFILES is set so that you can add a new log file group. If we have a third disk drive and want to add a third member to each group, we must check MAXLOGMEMBERS. So let’s add a third redo log group. We will use Server Manager to do this.
svrmgr> alter database add logfile group 3