Tuning Recovery - Expert Oracle RAC Performance Diagnostics and Tuning - page 330

■ underscore parameters are undocumented and should be set or modified only with prior approval from
oracle support. prior to oracle Database 11g release 2, _BACKUP_FILE_BUFCNT was called _BACKUP_KSFQ_BUFCNT , and
_BACKUP_FILE_BUFSZ was called _BACKUP_KSFQ_BUFSZ . 1

Caution

Fast Recovery Area
The fast recovery area (called flash recovery area in earlier versions of Oracle) is an Oracle-managed directory, file
system, or ASM diskgroup that provides a centralized disk location for backup and recovery files. All the files you need
to completely recover a database from a media failure are part of the fast recovery area.
Some of the recovery-related files stored in the fast recovery area include the following:

• Current control file

• Online redo logs

• Archived redo logs

• Flashback logs

• Control file autobackups

• Datafile and control file copies

• Backup pieces

Implementing the FRA (flash recovery area) feature involves configuring two important parameters.

DB_RECOVERY_FILE_DEST_SIZE specifies the maximum storage in bytes of data to be used by
the FRA for this database. Note, however, that this value does not include certain kinds of disk
overhead: Block 0 or the OS block header of each Oracle file is not included in this size. Allow
an extra 10% for this data when computing the actual disk usage required for the FRA.

•

DB_RECOVERY_FILE_DEST_SIZE does not indicate the real size occupied on disk when the
underlying file system is mirrored, compressed, or in some other way affected by overhead
not known to Oracle. For example, if you can configure the fast recovery area on a normal
redundancy (two-way mirrored) ASM disk group, each file of X bytes occupies 2X bytes on
the ASM disk group. In such a case, DB_RECOVERY_FILE_DEST_SIZE must be set to no more
than 1/2 the size of the disks for the ASM diskgroup. Likewise, when using a high redundancy
(three-way mirrored) ASM diskgroup, DB_RECOVERY_FILE_DEST_SIZE must be no more than
1/3 the size of the disks in the disk group, and so on.

•

As with any feature that requires storage space, the first step in the process is to size the storage area that would
contain the FRA data. Sizing should be based on what kind of files and to what retention level the files will be saved in

1 Chien, Timothy and Greg Green, “Recovery Manager (RMAN) Configuration and Performance Tuning Best Practices.” Oracle Open
World, 2010.