Umar DBA: RMAN and Flash Recovery Area

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PURPOSE

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  This article is about how RMAN uses the Flash Recovery Area incase

  of a backup and restore.

SCOPE & APPLICATION

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  New Feature in oracle 10G and for DBAs, support

OVERVIEW

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Once a Flash Recovery Area is configured, RMAN will than use the Flash Recovery Area

to store backups; thus, RMAN backups are stored initialy on disk and not on tape.

Space management of the Flash Recovery Area is descibed in :

  Note 315098.1 How is the space pressure managed in the Flash Recovery Area

The Flash Recovery Area can be a filesystem or a directory, however alternatively,

it can be an Automatic Storage Management (ASM) diskgroup.

In that case, the Flash Recovery Area is specified by:

SQL> alter system set db_recovery_file_dest = '+dskgrp1';

Consequently, using ASM and RMAN in combination, you can build a

highly scaleable, fault-tolerant storage system using cheap disks

such as Serial ATA or SCSI drives, with no additional software required

This approach not only makes the backup process much faster but also cheap

enough to compete with the tape-based approach. An additional benefit is

protection against user errors. Because ASM files are not true filesystems,

they are less likely to be corrupted accidentally by DBAs and sysadmins.

Files Created by RMAN Commands in the Flash Recovery Area

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RMAN commands or implicit actions (such as controlfile autobackup)

can create files in the Flash Recovery Area.

Other files which are stored in the Flash Recovery Area, but out of the

control of RMAN, are :

   - Flashback logs

   - Archived redologs

   - Data-, redolog- and controlfiles

The related RMAN commands are:

- BACKUP

  Per default a backuppiece is created in the Flash Recovery Area unless

  it is overruled by using the FORMAT-clause.

  The FORMAT-clause can be specified in the BACKUP command or configured

  in the persistent configuration, by using CONFIGURE command.

  The default name of a backuppiece will be in Oracle Managed Files name format.

- Controlfile Autobackup

  RMAN can enable controlfile autobackups.

  RMAN> configure controlfile autobackup on;

  Like with normal backup, the Controlfile autobackup will be stored in the

  Flash Recovery Area unless the location is overruled by the FORMAT for

  the autobackup.

  RMAN> configure controlfile autobackup format for device type disk to <....>;

- RESTORE ARCHIVELOG

  Per default RMAN restores the archived redologs in the LOG_ARCHIVE_DEST_n

  location.  If one of the LOG_ARCHIVE_DEST_n parameters is set to

  "LOCATION=USE_DB_RECOVERY_FILE_DEST" then restored archived

  redo log files will be stored in the Flash Recovery Area.

  This can be overrulled by using the RMAN command :

  RMAN> SET ARCHIVELOG DESTINATION <....>;

- RECOVER DATABASE or TABLESPACE, BLOCKRECOVER & FLASHBACK DATABASE

  These commands restore archived redologs from the backup to be used for

  the media recovery, as required by the command. RMAN restores the needed

  archived redologs and deletes them once they are applied during media recovery.

  The location of the restored archived redolog is handle as if it is

  a explicit RESTORE ARCHIVELOG as described above.

REFERENCE

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Note 305817.1 FAQ - Flash Recovery Area feature of 10G

Umar DBA