（1）手动模拟删除onlinelog状态为inactive。
sql> select * from v$log;
sql> alter database open;
alter database open
*
error at line 1:
ora-03113: end-of-file on communication channel
检查alert文件：
errors in file /u01/app/oracle/admin/racdb/bdump/racdb1_lgwr_24441.trc:
ora-00313: open failed for members of log group 1 of thread 1
ora-00312: online log 1 thread 1: '+rac_disk/racdb/onlinelog/group_1.260.795090071'
ora-17503: ksfdopn:2 failed to open file +rac_disk/racdb/onlinelog/group_1.260.795090071
ora-15012: asm file '+rac_disk/racdb/onlinelog/group_1.260.795090071' does not exist
ora-00312: online log 1 thread 1: '+rac_disk/racdb/onlinelog/group_1.261.795090069'
ora-17503: ksfdopn:2 failed to open file +rac_disk/racdb/onlinelog/group_1.261.795090069
ora-15012: asm file '+rac_disk/racdb/onlinelog/group_1.261.795090069' does not exist
thu sep 27 11:08:00 2012
arc0: starting arch processes
thu sep 27 11:08:00 2012
errors in file /u01/app/oracle/admin/racdb/udump/racdb1_ora_24735.trc:
ora-00313: open failed for members of log group 1 of thread 1
ora-00312: online log 1 thread 1: '+rac_disk/racdb/onlinelog/group_1.261.795090069'
ora-00312: online log 1 thread 1: '+rac_disk/racdb/onlinelog/group_1.260.795090071'
报错中显示找不到onlinelog。
（2）由于onlinelog必须存在2个组，，所以先增加新group，再删除丢失的group。
sql> alter database add logfile thread 1 group 5;
sql> alter database drop logfile group 1;
sql> alter database open;
sql> alter system switch logfile;