Online redo logs can be created in multiple disk groups, either implicitly in an initialization parameter file or explicitly in an ALTER DATABASE...ADD LOGFILE statement. Each online log should have one log member in multiple disk groups. The file names for log file members are automatically generated. All partially created redo log files, created because of a system error, are automatically deleted.
For example, if there are disk groups named data1 and data2, you can create a log file with a member in each disk group with the following SQL statement:
SQL> ALTER DATABASE ADD LOGFILE (+data1,+data2);
The following example creates a log file with a member in each of the disk groups data1 and data2. These parameter settings are included in the initialization parameter file:
DB_CREATE_ONLINE_LOG_DEST_1 = +data1 DB_CREATE_ONLINE_LOG_DEST_2 = +data2
The following statement can be run at the SQL prompt:
SQL> ALTER DATABASE ADD LOGFILE;