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Lesson 5Backup Strategies
Objective Describe the backup strategies available using the Backup Wizard.

Database Backup Strategies

The Backup Wizard within OEM provides the following two strategies for backing up a database:
  1. Predefined strategy
  2. Customized strategy

Within the predefined backup strategy, a complete backup of the database, including the archive log files, is performed. The user can choose the frequency, start, and location(s) of the backup. Within the customized strategy, the user specifies at each step how, when, and where the backup must be performed.

Predefined Backup Strategy

By selecting the predefined backup, the user eliminates the choice of elements to be backed up. The user only specifies the details for when and where the backup has to be done. The following panels appear when you choose a predefined backup strategy:
  1. Backup Wizard: Backup Frequency: The Backup Frequency page allows you to specify how often you want to perform a backup and on which day of the week.
  2. Backup Wizard: Backup Time: The Backup Time page allows you to specify the start time for performing the backup.
  3. Backup Wizard: Configuration: The Configuration page allows you to choose the configuration for backup and view the details that you have set up previously using the Create Backup Configuration option.
  4. Backup Wizard: Multiple Destination: The Multiple Destination page allows you to specify the destination database(s) to submit the job. You can choose from the list of databases shown on the Available Databases window.

Database running in ARCHIVELOG mode

If your database is running in ARCHIVELOG mode, the backup is taken when the database is open. When you run a database in ARCHIVELOG mode, you allow Oracle to archive the online redo log. You can either perform the archiving manually or enable automatic archiving. If the database is running in NOARCHIVELOG mode, the backup job closes the database, takes the backup, and then reopens the database. When you run your database in NOARCHIVELOG mode, you disable the archiving of the online redo log. The choice of whether to enable the archiving of filled groups of online redo log files depends on the availability and reliability requirements of the application running on the database.
  1. Customized backup strategy: A customized backup strategy allows you to select the information you want to backup and to determine the schedule for the execution of the backup.
  2. Backup Wizard: backup selection: Your database contains a wide variety of types of data. When developing your backup strategy, you must determine the information you want to backup. The basic principle you should use when deciding is to prioritize the data depending on its importance and the degree to which it changes.

Once you have prioritized the data to back up, you can choose from the following basic backup types:
  1. Entire database: The entire database backup contains the control file along with all the database files that belong to a database. Entire database backup is the most common type of backup. This option backs up the entire database at once. If you operate in ARCHIVELOG mode, you also have the option of backing up different parts of the database over a period of time, thereby constructing an entire database backup piece by piece.
  2. Tablespace: A tablespace backup is a backup of a subset of the database. Tablespace backups are valid only if the database is operating in ARCHIVELOG mode.
  3. Datafile: A datafile backup is a backup of a single datafile. Datafile backups, which are not as common as tablespace backups, are valid only if you run the database in ARCHIVELOG mode.
  4. Archived redo log: An archived redo log is an online redo log that Oracle has filled with redo entries, rendered inactive, and copied to one or more log archive destinations. Archive redo logs do not change, for example, but they are crucial for recovering your database, so you should maintain multiple copies if possible. This option is available only in ARCHIVELOG mode.

Backup Wizard: Backup Options

The Backup Options page allows you to choose from a full or an incremental backup.
  1. Full backup: A full backup backs up all blocks into the backup set, skipping only datafile blocks that have never been used. The server process does not skip blocks when backing up archived redo logs or control files. A full backup has no effect on subsequent incremental backups, which is why it is not considered part of the incremental strategy. In other words, a full backup does not affect which blocks are included within subsequent incremental backups.
  2. Incremental backup: Incremental backups are a method by which you only backup modified blocks. An incremental level 0 backup performs the same function as a full backup in that both backup all blocks that have never been used; except a level 0 will affect what blocks are copied out by subsequent incremental backups. Incremental backups of levels greater than 0 back up only blocks that have changed since previous incremental backups. Blocks that have not changed will not be backed up.
    1. Non-cumulative backup: A type of incremental backup in which you back up all blocks that have changed since the most recent backup at level n or lower. For example, in a differential level 2 backup, you back up all blocks modified since the last level 2, level 1, or level 0 backup. A non-cumulative backup copies less data, and therefore, takes a shorter time than the cumulative backup, but recovery time is longer.
    2. Cumulative backup: A type of incremental backup that allows you to back up all the blocks used since the most recent backup at level n-1 or lower. For example, within a cumulative level 2 backup, you back up all blocks used since the most recent level 1 or level 0 backup. A cumulative backup copies more data, and therefore, takes longer than the non-cumulative backup, but the recovery time is shorter.

Throughout this course we have emphasized how important it is to develop a solid backup plan. This lesson has illustrated the variety of backup options that Oracle provides. Now let us look at how we can implement them.
The next lesson configures and schedules a backup using Backup Wizard.

Oracle Backup and Recovery