DB_CREATE_ONLINE_LOG_DEST_n

官方地址：http://docs.oracle.com/cd/B19306_01/server.102/b14237/initparams045.htm#REFRN10035

DB_CREATE_ONLINE_LOG_DEST_n

Property	Description
Parameter type	String
Syntax	DB_CREATE_ONLINE_LOG_DEST_[1 | 2 | 3 | 4 | 5] = directory | diskgroup
Default value	There is no defaultvalue.
Modifiable	ALTERSESSION , ALTER SYSTEM
Basic	Yes

DB_CREATE_ONLINE_LOG_DEST_n (where n = 1, 2, 3, ... 5) specifiesthe default location for Oracle-managed control files and onlineredo logs. If more than one DB_CREATE_ONLINE_LOG_DEST_n parameteris specified, then the control file or online
redo log ismultiplexed across the locations of the otherDB_CREATE_ONLINE_LOG_DEST_n parameters. One member of each onlineredo log is created in each location, and one control file iscreated in each location. Specifying at least two parametersprovides greater
fault tolerance for the control files and onlineredo logs if one of the locations should fail.Ifa file system directory is specified as the default location, thenthe directory must already exist; Oracle does not create it. Thedirectory must have appropriate
permissions that allow Oracle tocreate files in it. Oracle generates

unique names for the files, and a file thus created is anOracle-managed file.db_recovery_file_dest 参数启用redo、control、rmanbackups、archived logs、flashback logs 文件的omf管理,类似的db_create_online_log_dest_n 参数启用redo、control的omf管理,从中我们也可以看出redo、control 文件的重要性！！这三个参数对redo、control

文件位置的影响：

1.位置优先级：【control_files 初始化参数】 >db_create_online_log_dest_n >db_recovery_file_dest>= db_create_file_dest

此处的等于号比较有意思：如果没有db_create_online_log_dest_n,而存在

db_create_file_dest 时，db_recovery_file_dest 就相当

db_create_online_log_dest_2，db_create_file_dest 则相当于

db_create_online_log_dest_1

2.redo 文件的多路复用

通常应该通过指定db_create_online_log_dest_n 来达到该目的！