SQL> select * from v$logfile;
GROUP# STATUS TYPE MEMBER IS_
---------- ------- ------- --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ---
1 ONLINE /u03/oracle/11.2/sachin/redo_01/sachin_redo01.log NO
2 ONLINE /u05/oracle/11.2/sachin/redo_02/sachin_redo02.log NO
3 ONLINE /u04/oracle/11.2/sachin/sachin_redo03.log
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES BLOCKSIZE MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIME NEXT_CHANGE# NEXT_TIME
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- ------------------ ------------ ------------------
1 1 40 52428800 512 1 YES INACTIVE 1124953 11-JUL-16 1173375 12-JUL-16
2 1 41 52428800 512 1 YES INACTIVE 1173375 12-JUL-16 1220390 13-JUL-16
3 1 42 52428800 512 1 NO CURRENT 1220390 13-JUL-16 2.8147E+14
SQL> alter database add logfile member '/u03/oracle/11.2/sachin/redo_01/sachin_redo01B.log' to group 1;
Database altered.
SQL> alter database add logfile member '/u03/oracle/11.2/sachin/redo_01/sachin_redo02B.log' to group 2;
Database altered.
SQL> alter database add logfile member '/u03/oracle/11.2/sachin/redo_01/sachin_redo03B.log' to group 3;
Database altered.
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES BLOCKSIZE MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIME NEXT_CHANGE# NEXT_TIME
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- ------------------ ------------ ------------------
1 1 40 52428800 512 2 YES INACTIVE 1124953 11-JUL-16 1173375 12-JUL-16
2 1 41 52428800 512 2 YES INACTIVE 1173375 12-JUL-16 1220390 13-JUL-16
3 1 42 52428800 512 2 NO CURRENT 1220390 13-JUL-16 2.8147E+14
SQL> select * from v$logfile;
GROUP# STATUS TYPE MEMBER IS_
---------- ------- ------- --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ---
1 ONLINE /u03/oracle/11.2/sachin/redo_01/sachin_redo01.log NO
2 ONLINE /u05/oracle/11.2/sachin/redo_02/sachin_redo02.log NO
3 ONLINE /u04/oracle/11.2/sachin/sachin_redo03.log NO
1 INVALID ONLINE /u03/oracle/11.2/sachin/redo_01/sachin_redo01B.log NO
2 INVALID ONLINE /u03/oracle/11.2/sachin/redo_01/sachin_redo02B.log NO
3 INVALID ONLINE /u03/oracle/11.2/sachin/redo_01/sachin_redo03B.log NO
6 rows selected.
SQL>
Member provide the redundancy for logfile if one logfile will crash the it will recover from redundancy and db will not stop.