使用RMAN 备份 standby database  ,在主库出现数据文件丢失的时候对主库进行恢复.
  1) 在主库上对备库进行备份:( 注意使用 nocatalog)
   $: rman nocatalog target sys/oracle@clon (连接到备库)
      rman> run {
                  allocate channel c1 device type disk;
                  backup as compressed backupset
                  format '/u1/backup/db_stb_%T_%s_%p.dbf'
                  tag='db_stb'
                  database ;
                  backup as compressed backupset
                  format '/u1/backup/arc_stb_%T_%s_%p.dbf'
                  archivelog all delete input
                  tag='arc_stb';
                 }
 2) 将备库的备份集 copy 到主库的相同的目录下.
    $: scp /u1/backup/*  @test:/u1/backup
 3) 在主库上打开恢复目录数据库 rman ,然后同步备库的备份信息到恢复目录数据库里.
    $: rman catalog rman/rman@rman target sys/oracle@clon
      rman>  crosscheck backup;
      rman>  delete expired backup;
      rman>  resync catalog ;
      rman>  list backup summary;
 4) 在主库上做破坏,删除数据文件 users01.dbf (对应的数据文件号是 4)
    $:    rm users01.dbf
    sql>  select status from v$datafile ; ( 文件4是  ONLINE) 
    sql>  alter database datafile 4 offline;
    sql>  alter database datafile 4 online ;
    sql>  select status from v$datafile ; ( 文件4 是 RECOVERY)
 5) 同步主库的信息到恢复目录数据库里
    $: rman catalog rman/rman@rman  target sys/oracle@lmj
    rman>  crosscheck backup;
    rman>  delete expired backup;
    rman>  resynce catalog ;
 6) 进行主库的恢复:
   $:  rman catalog rman/rman@rman  target sys/oracle@lmj
       rman>  run {
                    allocate channel c1 device type disk;
                    restore datafile 4 ;
                    recover datafile 4 ;
                    sql " alter database datafile 4 online";
                   }