Oracle可以设置备用归档路径，如果首要归档路径不可用，可以自动切换到备用路径，而平时备用路径不启用，这在一些对高可用要求比较高的环境中还是有实用价值，无法正确归档将会导致数据库挂起。启用该特性需要配置的参数如下：
log_archive_dest_1='location=/arc/archive/test alternate=log_archive_dest_2 noreopen'
log_archive_dest_2='location=/arc1/archive/test'
log_archive_dest_state_1=enable
log_archive_dest_state_2=alternate
log_archive_dest_1需要设置noreopen或者reopen=0属性，否则无法迅速切换到备用路径，可能导致数据库无法归档。
此时归档路径状态如下：
SQL> select dest_name,destination,status,error from v$archive_dest;
DEST_NAME DESTINATION STATUS ERROR
-------------------- ------------------ ---------- ---------------------
LOG_ARCHIVE_DEST_1 /arc/archive/test VALID
LOG_ARCHIVE_DEST_2 /arc1/archive/test ALTERNATE
LOG_ARCHIVE_DEST_3 standby VALID
LOG_ARCHIVE_DEST_4 INACTIVE
LOG_ARCHIVE_DEST_5 INACTIVE
LOG_ARCHIVE_DEST_6 INACTIVE
LOG_ARCHIVE_DEST_7 INACTIVE
LOG_ARCHIVE_DEST_8 INACTIVE
LOG_ARCHIVE_DEST_9 INACTIVE
LOG_ARCHIVE_DEST_10 INACTIVE
正常情况下，数据库会归档到/arc/archive/test目录下，如果/arc/archive/test目录不可用，则归档会报一次错，然后会切换到第二个备用路径/arc1/archive/test。
SQL> alter system archive log current;
alter system archive log current
*
ERROR at line 1:
ORA-16038: log 5 sequence# 2496 cannot be archived
ORA-19504: failed to create file ""
ORA-00312: online log 5 thread 1: '/u01/oracle/oradata/ningoo/redo05_01.dbf'
ORA-00312: online log 5 thread 1: '/u01/oracle/oradata/ningoo/redo05_02.dbf'
SQL> alter system archive log current;
System altered.
此时再看归档目标的状态，可以发现oracle自动做了修改，第一个失效路径被diable，而第二个备用路径被enable：
SQL> select dest_name,destination,status,error from v$archive_dest;
DEST_NAME DESTINATION STATUS ERROR
------------------- ------------------- ---------- -------------------------------------
LOG_ARCHIVE_DEST_1 /arc/archive/test DISABLED ORA-19504: failed to create file ""
LOG_ARCHIVE_DEST_2 /arc1/archive/test VALID
LOG_ARCHIVE_DEST_3 standby VALID
LOG_ARCHIVE_DEST_4 INACTIVE
LOG_ARCHIVE_DEST_5 INACTIVE
LOG_ARCHIVE_DEST_6 INACTIVE
LOG_ARCHIVE_DEST_7 INACTIVE
LOG_ARCHIVE_DEST_8 INACTIVE
LOG_ARCHIVE_DEST_9 INACTIVE
LOG_ARCHIVE_DEST_10 INACTIVE
注意，即使现在第一个归档路径恢复正常，也不会再自动切换回去，需要手工重新修改路径状态参数
log_archive_dest_state_1=enable
log_archive_dest_state_2=alternate
如果第一个主要归档目的地是NFS，则NFS主机down或者网络down的时候，在os上ls或者df都会hang住，但Oracle依然可以实现切换到备用归档路径，只是需要的时间稍长，在我的测试中大概花了10s左右才成功归档，并且alert会报错：
Errors in file /u01/oracle/admin/test/udump/test_ora_192654.trc:
ORA-07286: sksagdi: cannot obtain device information.
IBM AIX RISC System/6000 Error: 78: Connection timed out
切换成功后查看归档路径的状态如下：
SQL>select dest_name,destination,status,error from v$archive_dest;
DEST_NAME DESTINATION STATUS ERROR
-------------------- --------------------- ---------- -----------------------------------
LOG_ARCHIVE_DEST_1 /arc/test/test DISABLED ORA-16032: parameter destination
string cannot be translated
LOG_ARCHIVE_DEST_2 /arc1/archive/test VALID
LOG_ARCHIVE_DEST_3 standby VALID
LOG_ARCHIVE_DEST_4 INACTIVE
LOG_ARCHIVE_DEST_5 INACTIVE
LOG_ARCHIVE_DEST_6 INACTIVE
LOG_ARCHIVE_DEST_7 INACTIVE
LOG_ARCHIVE_DEST_8 INACTIVE
LOG_ARCHIVE_DEST_9 INACTIVE
LOG_ARCHIVE_DEST_10 INACTIVE
另外，设置归档路径到NFS，AIX会报错：
ORA-27054: NFS file system where the file is created or resides is not mounted with correct options
这是bug，设置event=’10298 trace name context forever, level 32′可以绕过NFS的mount选项检查。Note:420582.1上说将mount信息写到/etc/filesystems可以避过，但在我的测试中无效。
