How to recover from a loss of all redo log members of an INACTIVE group

Let's simulate a loss of all redo log members of an inactive group.
If you have completely lost one redo log group your database won't be able to open.
Next thing is to know the STATUS of the lost redo log group (we know it because we are simulating the loss, but...) and, just because this information is on V$LOG view, try to get also the ARCHIVED column.
Now if the redo log group lost was INACTIVE and archived (YES value) we can simply recreate all members with the "alter database clear logfile" command;
if it was INACTIVE and not archived (NO value) we'll execute the "alter database clear unarchived logfile" command.

Let's look at the example. Here is my redo log group state

SQL> select member, a.group#, a.status, b.status, a.archived  from v$log a, v$logfile b where  a.group# = b.group# order by a.group#, member;

MEMBER                                                           GROUP# STATUS           STATUS  ARC
------------------------------------------------------------ ---------- ---------------- ------- ---
/home/oracle/app/oracle/oradata/orcl/redo01.log                       1 INACTIVE                 YES
/home/oracle/app/oracle/oradata/orcl/redo01b.log                      1 INACTIVE                 YES
/home/oracle/app/oracle/oradata/orcl/redo02.log                       2 CURRENT                  NO
/home/oracle/app/oracle/oradata/orcl/redo02b.log                      2 CURRENT                  NO
/home/oracle/app/oracle/oradata/orcl/redo03.log                       3 INACTIVE                 YES
/home/oracle/app/oracle/oradata/orcl/redo03b.log                      3 INACTIVE                 YES

Delete all members of redo log group 1 and kill your instance.

[oracle@localhost ~]$ rm /home/oracle/app/oracle/oradata/orcl/redo01*
[oracle@localhost ~]$ ps -ef |grep smon
oracle    8176     1  0 06:44 ?        00:00:03 ora_smon_orcl
oracle    9057  3164  0 08:10 pts/5    00:00:00 grep smon
[oracle@localhost ~]$ kill -9 8176

Try to open your database ...

SQL> startup
ORACLE instance started.

Total System Global Area  456146944 bytes
Fixed Size                  1344840 bytes
Variable Size             385878712 bytes
Database Buffers           62914560 bytes
Redo Buffers                6008832 bytes
Database mounted.
ORA-03113: end-of-file on communication channel
Process ID: 9184
Session ID: 17 Serial number: 7

... and look at your alert log

...
ORA-00313: open failed for members of log group 1 of thread 
ORA-00312: online log 1 thread 1: '/home/oracle/app/oracle/oradata/orcl/redo01.log'
ORA-00312: online log 1 thread 1: '/home/oracle/app/oracle/oradata/orcl/redo01b.log'
USER (ospid: 9184): terminating the instance due to error 313
...

Start your database in MOUNT mode

SQL> startup mount
ORACLE instance started.

Total System Global Area  456146944 bytes
Fixed Size                  1344840 bytes
Variable Size             385878712 bytes
Database Buffers           62914560 bytes
Redo Buffers                6008832 bytes
Database mounted.

Query the V$LOG view

SQL> select member, a.group#, a.status, b.status, a.archived  from v$log a, v$logfile b where  a.group# = b.group# order by a.group#, member;

MEMBER                                                           GROUP# STATUS           STATUS  ARC
------------------------------------------------------------ ---------- ---------------- ------- ---
/home/oracle/app/oracle/oradata/orcl/redo01.log                       1 INACTIVE                 YES
/home/oracle/app/oracle/oradata/orcl/redo01b.log                      1 INACTIVE                 YES
/home/oracle/app/oracle/oradata/orcl/redo02.log                       2 CURRENT                  NO
/home/oracle/app/oracle/oradata/orcl/redo02b.log                      2 CURRENT                  NO
/home/oracle/app/oracle/oradata/orcl/redo03.log                       3 INACTIVE                 YES
/home/oracle/app/oracle/oradata/orcl/redo03b.log                      3 INACTIVE                 YES

The redo log group 1 is INACTIVE and ARCHIVED so simply issue the following command:

SQL> alter database clear logfile group 1;

Database altered.

Open your database

SQL> alter database open;

Database altered.

If you are in the situation to have lost an INACTIVE and NOT already ARCHIVED redo log group then your command should be the following:

SQL> alter database clear unarchived logfile group 1;

Database altered.

Next step is to perform a complete backup

RMAN> backup database;

That's all.