Direct mode does not support RAC.YOU can connect only to one fixed server
in RAC.
ODAC 控件中的Direct模式不支持Oracle RAC,只能够链接一个确定的RAC实例。
如果要使用ODAC控件连接Oracle RAC,则需要Oracel安装客户端，并且不使用Direct模式，
链接方式与ADO连接Oracle一致。

根据说明，安装Oracle客户端，安装好之后，查找tnsnames.ora文件
在文件增加

DMSII=
 (DESCRIPTION =
 (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.73)(PORT = 1521))
              (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.74)(PORT = 1521))
               (LOAD_BALANCE = ON)
              (FAILOVER = ON)
             (CONNECT_DATA =
                      (SERVICE_NAME = DMSII)
                      (FAILOVER_MODE =
                              (TYPE = select)
                               (METHOD = BASIC)
                             (RETRIES = 30)
                              (DELAY = 5)
                      )
             )
       )
注意，DMSII前不能有空格
程序代码修改
  orsn1.Username:=UserName;
  orsn1.Password:=PassWord;
  orsn1.Server:=服务名;
  orsn1.Connect;
链接即可。