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Oracle® Database Backup and Recovery Advanced User's Guide 10g Release 2 (10.2) Part Number B14191-02 |
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# Configuring the Flash Recovery Area: Advanced Topics

To take maximum advantage of the flash recovery area, it should be used to store and manage as many different types of file as possible: online redo logs, archived redo logs, control files and RMAN's own working files for backup and restore operations.

This section contains the following topics:

- Configuring Online Redo Log Creation in the Flash Recovery Area

- Configuring Control File Creation in the Flash Recovery Area

- Archived Redo Log Creation in the Flash Recovery Area

- RMAN File Creation in the Flash Recovery Area

## Configuring Online Redo Log Creation in the Flash Recovery Area

The following statements can create online redo logs in the flash recovery area:

- `CREATE DATABASE`

- `ALTER DATABASE ADD LOGFILE`

- `ALTER DATABASE ADD STANDBY LOGFILE`

- `ALTER DATABASE OPEN RESETLOGS`

The default size of an online log created in the flash recovery area is 100 MB. The log member filenames are automatically generated by the database.

The initialization parameters that determine where online redo log files are created are `DB_CREATE_ONLINE_LOG_DEST_``n`, `DB_RECOVERY_FILE_DEST` and `DB_CREATE_FILE_DEST`. Details of the effect of various combinations of these parameters on online redo log creation can be found inOracle Database SQL Reference in the description of the `LOGFILE` clause of the `CREATE` `DATABASE` statement.

## Configuring Control File Creation in the Flash Recovery Area

The initialization parameters `CONTROL_FILES`, `DB_CREATE_ONLINE_LOG_DEST_``n`, `DB_RECOVERY_FILE_DEST`, and `DB_CREATE_FILE_DEST` all interact to determine the location where the database control files are created.

For a full description of how these parameters interact, see the "Semantics" section of the description of `CREATE CONTROLFILE` in Oracle Database SQL Reference.

If the database creates an Oracle managed control file, and if the database uses a server parameter file, then the database sets the `CONTROL_FILES` initialization parameter in the server parameter file. If the database uses a client-side initialization parameter file, then you must set the `CONTROL_FILES` initialization parameter manually in the initialization parameter file.

## Archived Redo Log Creation in the Flash Recovery Area

It is recommended that you the use flash recovery area as an archived log location because the archived logs are automatically managed by the database. Whatever archiving scheme you choose, it is always advisable to create multiple copies of archived logs.

You have the following basic options, listed from most to least recommended:

1. Enable archiving to the flash recovery area only and use disk mirroring to create the redundancy needed to protect the archived redo logs.

2. Enable archiving to the flash recovery area and set other `LOG_ARCHIVE_DEST_``n` initialization parameter to locations outside the flash recovery area.

3. Set `LOG_ARCHIVE_DEST_``n` initialization parameters to archive only to non-flash recovery area locations.

If you want to use the flash recovery area, you cannot use the `LOG_ARCHIVE_DEST` and `LOG_ARCHIVE_DUPLEX_DEST` initialization parameters. You must use instead the `LOG_ARCHIVE_DEST_``n` parameters, which have somewhat different semantics. Once your database is using `LOG_ARCHIVE_DEST_``n`, you can configure a flash recovery area.

### Rules for Initialization Parameters Affecting Redo Log File Destinations

The interactions among different initialization parameters affecting redo log archiving desintations are as follows:

- If `LOG_ARCHIVE_DEST` (and, optionally, `LOG_ARCHIVE_DUPLEX_DEST`) is set, these parameters will specify the only redo log archiving destinations.

- If `DB_RECOVERY_FILE_DEST` is specified (that is, if a flash recovery area is configured) and no `LOG_ARCHIVE_DEST_``n` is specified, then `LOG_ARCHIVE_DEST_10` is implicitly set to the flash recovery area. (You can override this behavior by explicitly setting `LOG_ARCHIVE_DEST_10` to an empty string.)

- If you set any local destinations for `LOG_ARCHIVE_DEST_``n`, then archived redo logs are stored only in the destinations you specify using those parameters. In this case, redo log files are not archived in the flash recovery area by default. If you have a flash recovery area configured, you can explicitly add the flash recovery area to the set of archiving destinations by setting one of the `LOG_ARCHIVE_DEST_``n` parameters to `LOCATION=USE_DB_RECOVERY_FILE_DEST` (note that this does not have to be `LOG_ARCHIVE_DEST_10`).

- If you do not set any value for `LOG_ARCHIVE_DEST`, `LOG_ARCHIVE_DEST_``n`, or `DB_RECOVERY_FILE_DEST`, then the redo logs are archived to a default location that is platform-specific. On Solaris, for example, the default is `?/dbs.`

### Filenames for Archived Redo Log Files in the Flash Recovery Area

The generated filenames for the archived redo logs in the flash recovery area are Oracle Manged Filenames and are not determined by `LOG_ARCHIVE_FORMAT`.

## RMAN File Creation in the Flash Recovery Area

This section describes RMAN commands or implicit actions (such as control file autobackup) that can create files in the flash recovery area, and how to control whether a specific command creates files there or in some other destination. The assumption in all cases is that a flash recovery area has already been configured for your database. The commands are:

- `BACKUP`

  Do not specify a `FORMAT` option to the `BACKUP` command, and do not configure a `FORMAT` option for disk backups. In such a case, RMAN creates backup pieces and image copies in the flash recovery area, with names in Oracle Managed Files name format.

- Control File Autobackup

  RMAN can create control file autobackups in the flash recovery area. Use the RMAN command `CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK CLEAR` to clear any configured format option for the control file autobackup location on disk. Control file autobackups will be placed in the flash recovery area when no other destination is configured.

- `RESTORE ARCHIVELOG`

  Explicitly or implicitly (as in the case of ), set one of the `LOG_ARCHIVE_DEST_n`) parameters to '`LOCATION=USE_DB_RECOVERY_FILE_DEST`'. If you do not specify SET ARCHIVELOG DESTINATION to override this behavior, then restored archived redo log files will be stored in the flash recovery area.

- `RECOVER DATABASE` or `TABLESPACE`, `BLOCKRECOVER`, and `FLASHBACK DATABASE`

  These commands restore archived redo logs from backup for use during media recovery, as required by the command. RMAN restores any redo log files needed during these operations to the flash recovery area, and delete them once they are applied during media recovery.

  To direct the restored archived redo logs to the flash recovery area, set one of the `LOG_ARCHIVE_DEST_``n` parameters to '`LOCATION=USE_DB_RECOVERY_FILE_DEST`", and make sure you are not using `SET ARCHIVELOG DESTINATION` to direct restored archived logs to some other destination.