三个参数对 redo、control文件位置…

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.


NOTE:
DB_CREATE_ONLINE_LOG_DEST_n (where n = 1, 2, 3, ... 5) specifiesthe default
location for Oracle-managed control files and online redo logs. Ifmore than one
DB_CREATE_ONLINE_LOG_DEST_n parameter is specified, then thecontrol file or online
redo log is multiplexed across the locations of the other
DB_CREATE_ONLINE_LOG_DEST_n parameters. One member of each onlineredo log is
created in each location, and one control file is created in eachlocation.
Specifying at least two parameters provides greater fault tolerancefor the
control files and online redo logs if one of the locations shouldfail.
If a file system directory is specified as the default location,then the
directory must already exist; Oracle does not create it. Thedirectory must have
appropriate permissions that allow Oracle to create 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、rman backups、archivedlogs、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！！




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！
3. 如果三个参数指定相同的值会怎样？自己猜吧 ：）

4. omf 文件的命名规则
<_dest_参数路径>/<db_unique_name_or_db_name>/<datafile>/o1_mf_%t_%u_.dbf