A flash recovery area is a location in which Oracle Database can store and manage files
related to backup and recovery. It is distinct from the database area, which is a location
for the Oracle-managed current database files (datafiles, control files, and online redo
logs).

You specify a flash recovery area with the following initialization parameters:
■ DB_RECOVERY_FILE_DEST: Location of the flash recovery area. This can be a
directory, file system, or Automatic Storage Management (ASM) disk group. It
cannot be a raw file system.
In a RAC environment, this location must be on a cluster file system, ASM disk
group, or a shared directory configured through NFS.
■ DB_RECOVERY_FILE_DEST_SIZE: Specifies the maximum total bytes to be used
by the flash recovery area. This initialization parameter must be specified before
DB_RECOVERY_FILE_DEST is enabled.
In a RAC environment, the settings for these two parameters must be the same on all
instances.

You cannot enable these parameters if you have set values for the
LOG_ARCHIVE_DEST and LOG_ARCHIVE_DUPLEX_DEST parameters. You must
disable those parameters before setting up the flash recovery area. You can instead set
values for the LOG_ARCHIVE_DEST_n parameters. If you do not set values for local
LOG_ARCHIVE_DEST_n, then setting up the flash recovery area will implicitly set
LOG_ARCHIVE_DEST_10 to the flash recovery area.

Oracle recommends using a flash recovery area, because it can simplify backup and
recovery operations for your database.

指定闪回恢复区
1. DB_RECOVERY_FILE_DEST : 闪回恢复区的路径
2. DB_RECOVERY_FILE_DEST_SIZE : 闪回恢复区的大小
3. 当指定了LOG_ARCHIVE_DEST , LOG_ARCHIVE_DUPLEX_DEST参数时, 不能设置闪回恢复区的值