Mirroring with Backup (Oracle)


You can use mirrored disks to reduce the time taken for an offline backup with the Oracle database. If mirror disks are used, you can still do online and offline backups in the normal way, but there are additional aspects discussed in this section that you need to be aware of.

The method described here has the disadvantage that the database is not mirrored during the backup. If you must have disk mirroring all the time (for protection against disk failures) this method can be safely deployed if three-way mirroring is used.


  1. If you want to perform offline backups in a mirrored disk environment, proceed as follows:
    1. Shut down the database and split the disk mirror.
    2. Restart the database on one disk set and perform offline backup on the other disk set.

You can perform offline backups while the database is online. You have to first shut down the database, then split the disk mirror and then you can restart the database on just one disk set. Next, you usually mount the split-off disk set on another system and perform an offline backup.

The downtime for this method is the time taken to shut down the database, split the mirror, and then restart the database.

  1. If you want to perform online backups in a mirrored disk environment, proceed as follows:
    1. Put the tablespaces in backup mode and split the disk mirror.
    2. End backup mode and perform the backup on the split-off disk set.

If the split-off disk set is mounted on another system – possible for both the approaches outlined above – the backup processing load is removed from the production system, so there is no performance loss during backup.

  1. After the backup is finished, resynchronize the two disk sets. It can take a long time to resynchronize, leading to severe performance loss.

Use BRBACKUP with mirrored disks

BRBACKUP supports backup for mirrored disks, using the backup_types offline_split and online_split . BRBACKUP records information about backups in the database. For mirrored disks, BRBACKUP writes the information about the backup to the database running with the active disk set, while it backs up the files from the split-off disk set to tape.


You have reduced the downtime for an Oracle offline backup or reduced performance loss during an Oracle online backup.