NetVault Plug-in for Oracle 7.1

An RMAN Full Backup is a backup of a datafile that includes every allocated block in the file being backed up. A full backup of a datafile can be an image copy, in which case every data block is backed up. You can also store it in a backup set, in which case datafile blocks not in use may be skipped. An RMAN Full Backup cannot be part of an Incremental Backup strategy, that is, it cannot be the parent or base of a subsequent Incremental Backup.

Incremental Backup

An Incremental Backup of a datafile captures images of blocks in the datafile that have changed since a specific point in time, usually the time of a previous Incremental Backup. Incremental backups are generally smaller than full datafile backups, unless every block in the datafile is changed. RMAN Incremental Backups are only available for datafiles.

During media recovery, RMAN uses the block images from Incremental Backups to update changed blocks to their contents at the SCN where the block was created, and it does this in a single step. Without Incremental Backups, all changes must be applied one at a time from the archived redo logs. To reduce downtime, RMAN will always choose an Incremental Backup over reapplying individual changes stored in archived redo logs.

Multilevel Incremental Backups

RMAN’s Incremental Backups are multilevel. Each incremental level is denoted by a value of 0 or 1.

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Level 0 Incremental Backup – A Level 0 Incremental Backup, which is the base for subsequent Incremental Backups, copies all blocks containing data, backing up the datafile into a backup set just as a full backup would.

The only difference between a Level 0 Incremental Backup and a full backup is that a full backup cannot be included in an incremental strategy.

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Level 1 Incremental Backup – A Level 1 Incremental Backup can be either of the following types:

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Cumulative Incremental Backup – In a Cumulative Incremental Backup, RMAN backs up all the blocks used since the most recent Level 0 Incremental Backup. Cumulative Incremental Backups speed up restores by reducing the number of Incremental Backups that need to be included in the recovery process. Cumulative Backups require more space and time than Differential Backups because they duplicate the work done by previous backups at the same level.

Cumulative Backups are preferred over Differential Backups when recovery time is more important than disk space, because fewer Incremental Backups need to be applied during recovery.

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Differential Incremental Backup – In a Differential Incremental Backup, RMAN backs up all blocks that have changed since the most recent Cumulative or Differential Incremental Backup, whether at Level 1 or Level 0.

RMAN determines which Level 1 backup occurred most recently and backs up all blocks modified since that backup. If no Level 1 is available, RMAN copies all blocks changed since the Level 0 backup.

Differential Incremental Backups lead to longer restores because multiple Incremental Backups must be applied during recovery.

Archive Log backup

Archived redo logs are important for PIT Recovery and must be backed up regularly. You can back up the archive logs separately or together with the datafiles and other supported files. The plug-in also provides the option to force an additional log switch before backing up the archive logs and the option to delete the archive logs from the disk after backing them up to the backup sets.

Reviewing the Control File backup types

Protecting the Control File is critical in many recovery situations. Plug‑in for Oracle provides two methods for protecting the Control File: Manual Backups and Autobackups. However, when using the RMAN method, you can perform either Control File Autobackups or Manual Backups but not both. When the Control File Autobackups are enabled for a database, Manual Control File Backups are not available.

Manual Backups of Control File

Manual Backup of the Control File is supported by both the User Managed and RMAN backup methods.

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Manual Backup of Control File with User Managed backup method – With the User Managed backup method, the plug-in does not use the active Control File for backup and restore. During backup, the plug-in first saves a snapshot of the Control File to the user-specified Control File Save Filename (Full Path), and then backs up this copy of the Control File. This ensures that a consistent copy of the Control File is protected. During restoration, the plug-in restores the Control File to the Control File Save Filename (Full Path) to ensure that the active Control File is not inadvertently overwritten. You must manually copy this file to the original location as required. To make sure that a recent copy of the Control File is always available, include it with each User Managed backup.

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Manual Backup of Control File with RMAN backup method – When Control File Autobackups are disabled and the Control File node is explicitly selected on the NetVault Backup Selections page, the plug-in uses RMAN’s BACKUP CURRENT CONTROLFILE to back up the Control Files. To make sure that a recent copy of the Control File is always available, include it with each RMAN backup.

Autobackups of Control File

An Autobackup of the Control File also includes the SPFILE. The Autobackups are made after every RMAN-based backup or after making structural changes to the database such as adding a tablespace, altering the state of a tablespace or datafile, adding an online redo log, renaming a file, adding a redo thread, and so on.

Manual vs. Autobackups

A Manual Control File backup lets you restore a specific copy of a Control File and is ideal when data corruption has occurred and you need to restore the version most recently saved prior to data corruption. You are responsible for ensuring that the Control File is backed up with every RMAN-based backup and after every database structural change. While Manual Control File backups offer the ability to restore specific Control File backups, they cannot be used during disaster recovery or in multi-instance RAC environments.

Control File Autobackups provide the most reliability to ensure that there is always a recent backup of the Control File. In addition, they are required for disaster recovery and in multi-instance RAC environments.

Reviewing the other backup types

Other backup types include:

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Duplicate Database backup

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Flash Recovery Area (FRA) backups

Duplicate Database backup

A Duplicate Database backup lets the DBA create a duplicate or clone of a source database for special purposes that must not affect the overall backup and restore procedures for the source database. RMAN supports duplicating databases to increase a DBA’s flexibility when performing the following tasks:

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Testing backup and recovery procedures.

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Testing an upgrade to a new release of Oracle Database.

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Testing the effect of applications on database performance.

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Generating reports.

For example, you can duplicate the production database on hostA to hostB, and then use the duplicate database on hostB to practice restoring and recovering this database while the production database on hostA operates as usual.

The plug-in’s support for Oracle’s Database Duplication is backup-based duplication. For additional information on Oracle’s Duplicate Database functionality, refer to Duplicating a Database in the Oracle Database Backup and Recovery User’s Guide.