Add redo logs group in RAC 12c database

1) Check the status of redo logs

SQL> select group#,thread#,members,status from v$log;

    GROUP#    THREAD#    MEMBERS STATUS
---------- ---------- ---------- ----------------
         1          1          2 INACTIVE
         2          1          2 CURRENT
         3          2          2 CURRENT
         4          2          2 INACTIVE


2) Add the redo log Group 5 and 6

SQL> alter database add logfile thread 1 group 5 ('+DATA','+FRA') size 1024M;

Database altered.

SQL>

SQL> alter database add logfile thread 1 group 6 ('+DATA','+FRA') size 1024M;

Database altered.

SQL>

SQL> select group#,thread#,members,status from v$log;

    GROUP#    THREAD#    MEMBERS STATUS
---------- ---------- ---------- ----------------
         1          1          2 INACTIVE
         2          1          2 CURRENT
         3          2          2 CURRENT
         4          2          2 INACTIVE
         5          1          2 UNUSED
         6          1          2 UNUSED

6 rows selected.

Note : You can drop inactive redo log group but not CURRENT and ACTIVE.

SQL> Alter database drop logfile group 1;

Database altered.

SQL> alter database add logfile thread 2 group 7 ('+DATA','+FRA') size 1024M;

Database altered.

SQL> alter database add logfile thread 2 group 8 ('+DATA','+FRA') size 1024M;

Database altered.