由于一开始非正常关闭造成信息不一致，遇到此报错.
当重新打开数据库，使数据文件，控制文件，日志文件同步后，既可修改归档模式

[oracle@rac1 oracle]$ sqlplus /nolog

SQL*Plus: Release 11.2.0.3.0 Production on Thu Apr 17 07:00:37 2014

Copyright (c) 1982, 2011, Oracle.  All rights reserved.

SQL> connect / as sysdba
Connected.
SQL> shutdown abort
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.

Total System Global Area  630501376 bytes
Fixed Size                  2230992 bytes
Variable Size             209716528 bytes
Database Buffers          411041792 bytes
Redo Buffers                7512064 bytes
Database mounted.
SQL> alter database archivelog;
alter database archivelog
*
ERROR at line 1:
ORA-00265: instance recovery required, cannot set ARCHIVELOG mode

SQL> alter database archivelog;
alter database archivelog
*
ERROR at line 1:
ORA-00265: instance recovery required, cannot set ARCHIVELOG mode

SQL> alter database archivelog;
alter database archivelog
*
ERROR at line 1:
ORA-00265: instance recovery required, cannot set ARCHIVELOG mode

SQL> alter database archivelog;
alter database archivelog
*
ERROR at line 1:
ORA-00265: instance recovery required, cannot set ARCHIVELOG mode

SQL> alter database archivelog;
alter database archivelog
*
ERROR at line 1:
ORA-00265: instance recovery required, cannot set ARCHIVELOG mode

SQL> alter database archivelog;
alter database archivelog
*
ERROR at line 1:
ORA-00265: instance recovery required, cannot set ARCHIVELOG mode

SQL> alter database open
  2  ;

Database altered.

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.

Total System Global Area  630501376 bytes
Fixed Size                  2230992 bytes
Variable Size             213910832 bytes
Database Buffers          406847488 bytes
Redo Buffers                7512064 bytes
Database mounted.
SQL> alter database archivelog;

Database altered.