A.2 Backing Up to the Flash Recovery Area and to Tape: Basic Scenarios

A.2.2.1.1 Initial Setup

The only required setup is to create a flash recovery area with the required disk quota, and set the flash recovery area as a redo log archiving destination.

The formula for determining your disk quota depends upon the backup retenion policy. It is the same, however, whether your retention policy is based on redundancy or recovery window. Use the following formula:

Disk Quota = Size of 1 copy of the database 
             + size of 1 day's level 1 incremental backup
             + size of (Y+1) days of archived logs

where Y is the number of days that elapse between execution of BACKUP RECOVERY AREA in your backup scripts.

For this example, there is one backup script, executed every day, which creates a new incremental level 1 backup with that day's changes, rolls forward the level 0 backup using the level 1 backup from the previous day, and backs up all flash recovery area files to tape. Since the script backs up the flash recovery area to tape daily, the flash recovery area must be large enough to hold a copy of the database, the daily level 1 incremental backup, and two days' worth of archived redo logs.

The on-disk recovery window is one day. To recover to a point farther back than one day, RMAN must restore backups from tape.

A.2.2.1.2 Daily Script

After the initial setup, a typical daily RMAN backup script would look like the following:

# Execute each day of the week
# Roll forward the copy to most recent incremental backup SCN, which will
# be yesterday's incremental level 1 backup
RECOVER COPY OF DATABASE WITH TAG "daily_backup";
# Take incremental backups to flash recovery area (using default disk channel)
BACKUP INCREMENTAL LEVEL 1 FOR RECOVER OF COPY WITH TAG "daily_backup" DATABASE;
# Back up flash recovery area to tape
BACKUP RECOVERY AREA;
# delete obsolete backups on tape
DELETE OBSOLETE DEVICE TYPE sbt;

The following table describes how the contents of the flash recovery area and tape change as this script is run each day. The script rolls forward the level 0 database copy tagged as daily_backup to the SCN of the preceding day's incremental level 1 backup, then creates a new level 1 incremental backup with the previous day's changes. For example, when you run the script on Thursday, RMAN rolls forward the level 0 backup to the SCN of the incremental backup on Wednesday.

A.2.2.2.1 Initial Setup

Create your flash recovery area with the required disk quota and set up the flash recovery area as a redo log archiving destination. The formula for determining your disk quota depends upon the frequency of backups of the flash recovery area to tape, as follows:

Disk Quota = Size of 1 copies of the database 
           + size of (Y+1) days of archived logs

where Y is the number of days that elapse between execution of BACKUP RECOVERY AREA in your backup scripts.

For this example, assume that you take a full database backup once each week, and back up the flash recovery area to tape on all seven days of the week.

There are two scripts in this strategy. Use the first script at the beginning of each week (say, on Sunday) to create a full database backup, and the other script on the remaining days of the week (Monday through Saturday) to back up the flash recovery area contents (the archived redo logs for the day) to tape.

Note that both of the scripts in this strategy include the BACKUP RECOVERY AREA command, so that command is executed every day. For this example, Y=1, so the disk quota is the size of one copy of the database plus two days of archived redo logs.

A.2.2.2.2 Weekly Scripts

This RMAN backup script is executed once each week, on Sunday:

# Execute only once a week
# Take copy of database to flash recovery area
BACKUP AS COPY DATABASE;
# Take backup of flash recovery area to tape
BACKUP RECOVERY AREA;
# Delete obsolete backups on tape
DELETE OBSOLETE DEVICE TYPE sbt;
EXIT;

A.2.2.2.3 Daily Script

The RMAN script to be executed each day (Monday through Saturday) would look like the following:

# Execute 6 days/wk
# Take backup of flash recovery area to tape
BACKUP RECOVERY AREA;
# delete obsolete backups on tape
DELETE OBSOLETE DEVICE TPE sbt;

Because the entire flash recovery area is backed up to tape every day, the database may delete backups and archived redo log files from the flash recovery area whenever space is needed for new files. Between backups it may be difficult to predict exactly which files will still be in the flash recovery area, because files are deleted whenever space is needed.

A.2.2.3.1 Initial Setup

The minimum flash recovery area disk quota for this scenario is calculated with the following formula:

Disk Quota = Size of 1 copy of the database 
           + Size of 1 level 1 incremental backup with Y days of changes 
           + Size of (Y+1) days of archived redo logs

where Y is the number of days between backing up the flash recovery area to tape.

For this example, Y=7, so the disk quota must be at least the size of one copy of the database, one seven-day level 1 incremental backup, and eight days' worth of archived redo logs.

A.2.2.3.2 Weekly Script

The script that implement the Sunday backup for this strategy weekly parts of the backup is as follows:

# Execute once a week
# Roll forward the whole copy of the database to last incremental backup SCN
RECOVER COPY OF DATABASE WITH TAG "whole_db_copy";
# Make an incremental backup of the database to the flash recovery area.
BACKUP DEVICE TYPE DISK INCREMENTAL LEVEL 1 
       FOR RECOVER OF COPY WITH TAG "whole_db_copy" 
       DATABASE;
# Back up flash recovery area to tape
BACKUP RECOVERY AREA;
# delete obsolete backups on tape
DELETE OBSOLETE DEVICE TYPE sbt;

A.2.2.3.3 Daily Script

The daily script for this strategy is shown here:

# Execute 6 days/wk
# Back up flash recovery area to tape
BACKUP RECOVERY AREA;
# delete obsolete backups on tape
DELETE OBSOLETE DEVICE TYPE sbt;

The following table llustrates how the scripts maintain the recovery window. Assume for the purposes of this example that the week begins on Sunday.

A.2.2.4.1 Weekly Script

Here is the script to run once at the beginning of each week

# Execute only once a week
# backup database to tape
BACKUP DEVICE TYPE sbt INCREMENTAL LEVEL 0 DATABASE;
# delete obsolete backups on tape
DELETE OBSOLETE DEVICE TYPE sbt;
# backup recovery file destination to tape
BACKUP RECOVERY AREA;

A.2.2.4.2 Daily Script

This script executes each day of the week except for the first day, for example, Monday through Saturday:

# backup recovery file destination to tape
BACKUP RECOVERY AREA;
# Take incremental backups to flash recovery area
BACKUP DEVICE TYPE DISK INCREMENTAL LEVEL 1 DATABASE;

The following table illustrates how the scripts maintain the RMAN retention policy recovery window and how the disk quota is maintained. The recovery files that exist after the execution of the script each day also exist on tape, so Oracle can delete files from the flash recovery area as needed.