ORA-01184: logfile group 5 already exists

Command:  

ALTER DATABASE ADD LOGFILE THREAD 2 GROUP 11 (‘+DATA’) size 52428800;

Error:

ORA-01184: logfile group 5 already exists

Troubleshoot:

SYS> SELECT thread#, group#
FROM gv$log;

THREAD# GROUP#
———- ———-
1                 1
1                 2
1                 3
1                 4
1                 5
1                 6
1                 7
1                 8
1                 9
1                 10

As we see there are just 10 groups.

Check standby redo logs:

SYS> SELECT group#
FROM v$standby_log;

GROUP#
———-
11

So we have standby redo log with group id 11.

Solution: 

Add logfile group with number more than 11.

I prefer to save numbers for standby logs and add new log with number 22(10 redo log groups+(10+1) recommended number of standby logs+ 1)

SYS> ALTER DATABASE ADD LOGFILE THREAD 2 GROUP 22 (‘+DATA’) SIZE 52428800;

Database altered.