Backing Up Your Database

Full Backups of Datafiles

A full backup of a datafile is a backup that includes all used blocks of the datafile. This backup can be either an image copy backup, which is an exact copy of the datafile as if copied with a host operating system file copy command, or a backup set created by RMAN. Regardless of the form in which the backup is stored, the entire datafile is backed up, even if only a few blocks have changed.

Incremental Backups of Datafiles

Incremental backups capture only those blocks that change between backups in each datafile. In a typical incremental backup strategy, a level 0 incremental backup is used as a starting point. A level 0 backup captures all blocks in the datafile.

Subsequent level 1 incremental backups, typically made at regular intervals such as once each day, capture images of each block in a datafile that changed. Level 1 backups can be cumulative, in which case all blocks changed since the most recent level 0 backup are included, or differential, in which case only those blocks changed since the most recent level 0 or level 1 incremental backup are included.

Recovering changed blocks from incremental backups is used to improve media recovery performance. Because an incremental level 1 backup captures the final contents of all datafile blocks changed during the period covered by the incremental, the recovery process can skip reapplying individual updates from the redo logs of that period and simply update each block with its final contents. The redo logs are only used for changes from the period not covered by level 1 incremental backups.

Incrementally Updated Backups: Rolling Forward Image Copies of Datafiles

The incrementally updated backups feature of Oracle lets you use one or more level 1 incremental backups with an older image copy backup of your datafiles. You can roll the old copy forward to the point in time of the last level 1 incremental backup. All blocks changed since the image copy was created are overwritten with their new contents as of the time of the last level 1 incremental backup. The effect is to roll the file forward in time, so that its contents are equivalent, for the purposes of database recovery, to an image copy full datafile backup made at the time of the last incremental level 1 backup.

Incorporating incrementally updated backups into your backup strategy shortens expected recovery times. The reason is that media recovery to the present time or a point in time in the recent past can begin at the time of the last level 1 backup applied rather than the time of the last full database backup. The Oracle-Suggested Strategy for backups is based upon incrementally updated backups.

Using Tags to Identify Backups

All RMAN backups, including incremental backups, can be labelled with a tag. A tag is a text string identifying that backup, either uniquely or as part of a group of backups. For instance, if you performed a weekly full database backup on Saturday nights, you could use the tag FULL_SATURDAY to identify all such backups. You can use these tags for referring to specific backups in RMAN commands; for example, you could issue a command to move the latest FULL_SATURDAY backup to tape.

Because you can use tags to refer to different groups of backups, you can create different routines in your overall backup strategy that do not interfere with each other. When you schedule a backup job and give the job a name, the job name is used to tag the backup.

Performing a Whole Database Backup with Oracle Enterprise Manager

Whole backups of a database are based on backing up the entire contents of the database at the time of backup. Full backups of all datafiles are created. The results may be stored as image copies or as backup sets, but in either case the complete contents of all datafiles of the database are represented in the backup, as well as the control file, archived redo log, and server parameter file. With this set of files, you can perform complete recovery of the database.

While whole database backups can be an important element in your overall backup strategy, they are also a required step in some situations, such as when you switch ARCHIVELOG mode on or off (see "Configuring ARCHIVELOG Mode For the Database").

To perform a whole database backup, follow these steps:

1. In the Backup/Recovery section of the Maintenance page, click Schedule Backup.

   The Schedule Backup page appears, as shown in .

   Figure 9-1 Schedule Backup Page

   
   Description of "Figure 9-1 Schedule Backup Page"
   
   

   The following sections of this page are important:

   • The Oracle-Suggested Backup section, where you can click Schedule Oracle-Suggested Backup to choose among backup strategies recommended by the database

   • The Customized Backup section, where you can schedule a one-time or repeated backup of database objects you select.

2. In the Customized Backup section, select Whole Database to make a full backup of your database immediately or schedule one as part of a user-designed backup strategy. Make sure the Username and Password fields are correct in the Host Credentials section and then click Schedule Customized Backup.

   The Schedule Customized Backup: Options page appears. In this page you specify the options for this whole database backup.

3. In the Backup Type section, select Full Backup. In the Backup Mode section, select either Online Backup or Offline Backup. Typically, you will want to perform online backups to maximize database availability.

   
   

   Note: As explained in "Configuring Your Database for Basic Backup and Recovery", you can only use online backups if your database is set up to run in ARCHIVELOG mode. In NOARCHIVELOG mode you can only perform offline backups.

   
   

   In the Advanced section, make the following selections:

   • Check Also back up all archived logs on disk if you are performing an online backup. There is no need to back up archived logs when performing an offline backup because the database is in a consistent state at the time of backup and does not require media recovery if you restore from this backup. Nevertheless, you can include archived logs in the backup if you wish.

   • Do not check Delete all archived logs from disk after they are successfully backed up if a flash recovery area is your only archiving destination. In this case, redo logs that have been backed up are deleted automatically as space is needed for storage of other files. If you are using some other destination, it may be useful to check this option as part of managing backup storage.

   • Do not check Use proxy copy supported by media management software to perform a backup for now.

   • Do not check Delete obsolete backups if you use a flash recovery area for backup storage. In this case, obsolete backups are deleted automatically as space is needed for storage of other files. If you are using some other destination, it may be useful to check this option as part of managing backup storage.

   • Do not enter a value for Maximum Files per Backup Set.

   After making your selections, click Next.

   The Schedule Customized Backup: Settings page appears.

4. Select a backup destination. Oracle recommends backing up to disk when possible to minimize recovery time by minimizing restores from tape. Backups created on disk can be moved to tape later. Click Next.

   The Schedule Customized Backup: Schedule page appears.

5. Specify identifying information for the backup job (including a tag and a description for your reference), and specify when the tasks for this backup job are performed:

   • In the Job section of the page, you can enter values for Job Name and Job Description. Default values for the name and description are generated for you. If you want to provide a tag for this backup, however, then enter the desired tag in the Job Name field. The job name is used as a prefix for the backup tag for backups produced by this job.

     You can set Job Description to any descriptive text that is useful for your own reference.

   • In the Schedule section, specify when to start the backup and how often to repeat it. Leave the default start time of Immediately selected to run a backup immediately, or set Later and enter a time in the future. For recurring backup jobs, select options in the Repeat and Repeat Until sections. For one-time backups, select One Time Only and Indefinite.

     
     

     Note: For recurring jobs, it is useful to set a Job Name so that the resulting backups are easy to identify as part of an ongoing series. Use a descriptive tag, such as WEEKLY_FULL_BACKUP.

     
     

     When finished, click Next.

     The Schedule Customized Backup: Review page appears. This page presents a complete description of the backup job you specified in the previous pages.

6. You can perform one of the following actions:

   • Click the Back button to change these options.

   • Click Edit RMAN Script to view and, if desired, edit the RMAN commands that will be executed to perform your specified backup jobs.

   • Click Submit Job to add the specified backup job to the schedule (or to run it immediately, if you specified that the job should run immediately).

   • Click Cancel to stop the scheduled backup.

   In this example, click Submit Job.

   The Status page appears. This page should contain a message indicating that the job was successfully submitted.

7. Click View Job to monitor the progress of the backup job.

   The Execution page appears. This page contains a Summary section describing the job. The Logs section includes a table listing the progress of the various steps of the backup job. You can reload this page in your browser to monitor the ongoing progress of the job. In the Name column of the table in the Logs section, you can see what phase the RMAN job is in. Clicking on the name of the phase of the backup displays a page containing the RMAN output for that part of the job. From this page, click the Back button in your browser to return to the Execution page.

Using the Oracle-Suggested Backup Strategy

Enterprise Manager makes it easy to set up an Oracle-suggested backup strategy for backups to disk that protects your data and provides efficient recoverability to any point in the a recovery window of your choosing. (In the simplest case, examined in this section, this window is 24 hours.) The Oracle-suggested strategy leverages Oracle's incremental backup and incrementally-updated backup features to provide faster backups than whole database backups, and faster recoverability than is possible through applying database changes from the archived log to your datafiles.

The Oracle-suggested backup strategy is based on creating an image copy of your database. This copy is rolled forward by means of incrementally updated backups. Oracle Enterprise Manager schedules RMAN backups jobs for you to run during the overnight hours.

For each datafile, the strategy calls for backups as follows:

• At the beginning of day 1 of the strategy (the time the first scheduled job actually runs), an incremental level 0 datafile copy backup. It contains the datafile's contents at the beginning of day 1.

  In a restore-and-recovery scenario, the redo logs from day 1 can be used to recover to any point during day 1.

• At the beginning of day 2, an incremental level 1 backup is created, containing the blocks changed during day 1.

  In a restore-and-recovery scenario, this incremental level 1 can be applied to quickly roll forward the level 0 backup to the beginning of day 2, and redo logs can be used to recover to any point during day 2.

• At the beginning of each day n for days 3 and onwards, the level 1 backup from the beginning of day n-1 is applied to the level 0 backup. This brings the datafile copy to its state at the beginning of day n-1. Then, a new level 1 is created, containing the blocks changed during day n-1.

  In a restore-and-recovery scenario, this incremental level 1 can be applied to the datafile rolled forward on day n-1 to the beginning of day n, and redo logs can be used to recover the database to any point during day n.

The datafile copies used in the Oracle-suggested backup strategy are tagged with the tag ORA$OEM_LEVEL_0. The level 1 incremental backups for use in this strategy are created for use with datafile copies that are so labelled. You can safely implement other backup strategies without concern for interference from the backups for the Oracle suggested strategy.

There are also Oracle-suggested strategies that use tape backups along with disk backups, but those are beyond the scope of this chapter.

Scheduling Other Backup Tasks

After taking some time to understand the full range of available backup options as described in Oracle Database Backup and Recovery Basics, you may decide to schedule backup tasks beyond those used to implement the Oracle-suggested backup strategy.

While the particulars of specifying the job to perform differ for each type of backup, all backups begin from the Schedule Backup page shown in Figure 9-1. Here you can select any of several object types to back up. You can also back up existing backups in one destination to some other destination, such as moving backups from disk to tape.

Click Schedule Customized Backup to continue to the pages where you specify details such as objects to back up, required options and settings. The choices presented on these pages are determined by the type of objects being backed up. On each page, after you have made your selections, click Next to proceed to the next page.

After you have specified the options, you reach the Schedule Customized Backup: Schedule page, where you specify the times at which the job is to be performed, as well as the Job Name and Job Description.

When you are done with the job name, description and schedule, click Next to move on to the Schedule Customized Backup: Review page. After reviewing the options, either click Back to make changes, click Edit RMAN Script to make changes to the script, or click Submit Job to add the job to the schedule.