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Oracle® Database Backup and Recovery User's Guide
11g Release 1 (11.1)

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8 Backing Up the Database

This chapter explains how to perform the most basic backup tasks and implement backup strategies using RMAN. This chapter includes the following topics:

See Also:

Overview of RMAN Backups

This section provides an overview of RMAN backups.

Purpose of RMAN Backups

The primary purpose of RMAN backups is to protect your data. If a media failure or disaster occurs, then you can restore your backups and recover lost changes.

You can also make backups to preserve data for long-time archival, as explained in "Making Database Backups for Long-Term Storage", and to transfer data, as explained in the chapters included in Part VII, "Transferring Data with RMAN".

Basic Concepts of RMAN Backups

As explained in Chapter 7, "RMAN Backup Concepts", you can back up all or part of your database with the BACKUP command from within the RMAN client. Many of the techniques described in this chapter are also used in the Oracle-suggested backup strategy provided by Enterprise Manager and described in Oracle Database 2 Day DBA.

In many cases, after your database has been configured in accordance with your backup strategy, you can back up the database by entering the following command at the RMAN prompt:

RMAN> BACKUP DATABASE;

RMAN uses the configured settings, the records of previous backups, and the control file record of the database structure to determine an efficient set of steps for the backup. RMAN then carries out these steps.

As explained in "RMAN File Management in a Data Guard Environment", you can run RMAN backups at any database in a Data Guard environment. Any backup of any database in the environment is usable for recovery of any other database as long as the backup is accessible. You can offload all backups of database files, including control file backups, to a physical standby database and thereby avoid consuming resources on the primary database.

See Also:

Specifying Backup Output Options

If you specify only the minimum required options for an RMAN command such as BACKUP DATABASE, then RMAN determines the destination device, locations for backup output, and a backup tag automatically based on your configured environment and built-in RMAN defaults.

You can also provide arguments to BACKUP to override these defaults. The most typical options are described in the following sections:

See Also:

Chapter 9, "Backing Up the Database: Advanced Topics" to learn about advanced backup options such as duplexing and restarting backups

Specifying the Device Type for an RMAN Backup

The BACKUP command takes a DEVICE TYPE clause that specifies whether to back up to disk or tape device. The following example illustrates a backup to disk.

Example 8-1 Specifying Device Type DISK

BACKUP DATABASE 
  DEVICE TYPE DISK;

When you run BACKUP without a DEVICE TYPE clause, RMAN stores the backup on the configured default device (disk or SBT). You set the default device with the CONFIGURE DEFAULT DEVICE TYPE command described in "Configuring the Default Device for Backups: Disk or SBT".

Specifying Backup Set or Copy for an RMAN Backup to Disk

RMAN can create backups on disk as image copies or as backup sets. "Configuring the Default Type for Backups: Backup Sets or Copies" explains how to configure the default disk device. You can override this default with the AS COPY or AS BACKUPSET clauses. To back up to disk as image copies, use BACKUP AS COPY.

Example 8-2 Making Image Copies

BACKUP AS COPY
  DEVICE TYPE DISK 
  DATABASE;

To back up your data into backup sets, use the AS BACKUPSET clause. You can allow backup sets to be created on the configured default device, or direct them specifically to disk or tape, as shown in the following example.

Example 8-3 Making Backup Sets

BACKUP AS BACKUPSET 
  DATABASE;

BACKUP AS BACKUPSET 
  DEVICE TYPE DISK 
  DATABASE;

BACKUP AS BACKUPSET 
  DEVICE TYPE SBT 
  DATABASE;

Specifying a Format for RMAN Backups

RMAN provides a range of options to name the files generated by the BACKUP command. RMAN uses the following set of rules to determine the format of the output files, which are listed in order of precedence:

If a FORMAT parameter is specified on the BACKUP command, then this setting controls the generated filename.

For example, you can direct the output to a specific location, as shown in the following command:

BACKUP DATABASE 
  FORMAT "/disk1/backup_%U";  # specifies a location on the file system

In this case, backups are stored with generated unique filenames with the prefix /disk1/backup_. Note that the %U substitution variable, used to generate a unique string at this point in the filename, is required.

You can also use the FORMAT parameter to name an ASM disk group as backup destination, as shown in the following example:

BACKUP DATABASE 
  FORMAT '+dgroup1';  # specifies an ASM disk group

No %U is required in this case because Automatic Storage Management (ASM) generates unique file names as needed. However, you can specify %U if desired.

Note:

If you specify FORMAT when a flash recovery area is enabled, then RMAN obeys the FORMAT setting. If no location is specified in the FORMAT clause, then RMAN creates the backup in a platform-specific location.

If a FORMAT setting is configured for the specific channel used for the backup, then this setting controls the generated filename.

If a FORMAT setting is configured for the device type used for the backup, then this setting controls the generated filename.

If a flash recovery area is enabled during a disk backup, and if FORMAT is not specified, then RMAN creates the backup with an automatically generated name in the flash recovery area.

If none of the other conditions in this list apply, then the default location and filename format of the backup are platform-specific.

See Also:

Oracle Database Backup and Recovery Reference to learn about the FORMAT clause, and the installation guides in the Oracle Database documentation library to learn about the default file locations for your platform

Specifying Multiple Formats for Disk Backups

Typically, you do not need to specify a format when backing up to tape because the default %U variable generates a unique filename for tape backups. When backing up to disk, however, you can specify a format to spread the backup across several drives for improved performance. In this case, allocate one DISK channel for each disk drive and specify the format string on the ALLOCATE CHANNEL command so that the filenames are on different disks. For example, issue the following command:

RUN
{ 
  ALLOCATE CHANNEL disk1 DEVICE TYPE DISK FORMAT '/disk1/%d_backups/%U';
  ALLOCATE CHANNEL disk2 DEVICE TYPE DISK FORMAT '/disk2/%d_backups/%U';
  ALLOCATE CHANNEL disk3 DEVICE TYPE DISK FORMAT '/disk3/%d_backups/%U';
  BACKUP AS COPY DATABASE; 
} 

You can distribute backups in this manner by default in the future, by configuring channels as follows:

CONFIGURE DEVICE TYPE DISK PARALLELISM 3;
CONFIGURE DEFAULT DEVICE TYPE TO DISK;
CONFIGURE CHANNEL 1 DEVICE TYPE DISK FORMAT '/disk1/%d_backups/%U';
CONFIGURE CHANNEL 2 DEVICE TYPE DISK FORMAT '/disk2/%d_backups/%U';
CONFIGURE CHANNEL 3 DEVICE TYPE DISK FORMAT '/disk3/%d_backups/%U';
BACKUP AS COPY DATABASE;

Specifying Tags for an RMAN Backup

RMAN attaches a character string called a tag to every backup it creates, as a way of identifying the backup. You can either accept the default tag or specify your own with the TAG parameter of the BACKUP command.

About Backup Tags

User-specified tags are a useful way to indicate the purpose or usage of different classes of backups or copies. You can tag backup sets, proxy copies, datafile copies, or control file copies. For example, you can tag datafile copies that you intend to use in a SWITCH command as for_switch_only and file copies that should be used only for a RESTORE command as for_restore_only.

Tags do not need to be unique, so multiple backup sets or image copies can have the same tag, for example, weekly_backup. Assume that you specify that a datafile should be restored from backups that have a specific tag. If more than one backup of the requested file has the desired tag, then RMAN restores the most recent backup that has the desired tag, within any constraints on the RESTORE command.

In practice, tags are often used to distinguish a series of backups created as part of a single strategy, such as an incremental backup strategy. For example, you might create a weekly incremental backups with a tag such as BACKUP TAG weekly_incremental. Many forms of the BACKUP command let you associate a tag with a backup, and many RESTORE and RECOVER commands let you specify a tag to restrict which backups to use in the RESTORE or RECOVER operation.

If you do not explicitly specify a tag with the TAG parameter of the BACKUP command, then RMAN implicitly creates a default tag for backups (except for control file autobackups). The format of the tag is TAGYYYYMMDDTHHMMSS, where YYYY is the year, MM is the month, DD is the day, HH is the hour (in 24-hour format), MM is the minutes, and SS is the seconds. For example, a backup of datafile 1 may get the tag TAG20070208T133437. The date and time refer to when RMAN started the backup, in the time zone of the instance performing the backup. If multiple backup sets are created by one BACKUP command, then each backup piece has the same default tag.

Tags are stored in uppercase, regardless of the case used when entering them. The maximum length of a backup tag is 30 bytes. Tags cannot use operating system environment variables or use special formats such as %T or %D.

See Also:

Oracle Database Backup and Recovery Reference for the default format description in BACKUP ... TAG

Specifying Tags for Backup Sets and Image Copies

The characters in a tag must be limited to the characters that are legal in filenames on the target database file system. For example, Automatic Storage Management (ASM) does not support the use of the dash (-) in the filenames it uses internally, so a tag including a dash (such as weekly-incr) is not a legal tag name for backups in ASM disk groups.

When you tag a backup set, the tag is an attribute of each backup piece in a given copy of a backup set. If you create a multiplexed backup set, then each copy of the backup set gets the same tag. Example 8-4 creates one backup set with tag MONDAYBKP.

Example 8-4 Applying a Tag to a Backup Set

BACKUP AS BACKUPSET
  COPIES 1 
  DATAFILE 7
  TAG mondaybkp; 

When you specify a tag for image copies, the tag applies to each individual copy. Example 8-5 shows that copies of datafiles in tablespaces users and tools get the tag MONDAYCPY.

Example 8-5 Applying Tags to Image Copies


BACKUP AS COPY 
  TABLESPACE users, tools
  TAG mondaycpy;

You can use FROM TAG to copy an image copy with a specific tag, and then use TAG to assign the output copy a different tag. Example 8-6 creates new copies of all image copies of the database that have the tag full_cold_copy and gives the new copies the tag new_full_cold_copy.

Example 8-6 Assigning Tags to Output Copies

BACKUP AS COPY
  COPY OF DATABASE
    FROM TAG full_cold_copy
  TAG new_full_cold_copy;

Making Compressed Backups

For any use of the BACKUP command that creates backup sets, you can take advantage of RMAN support for binary compression of backup sets. Specify the AS COMPRESSED BACKUPSET option to the BACKUP command. The resulting backup sets are compressed with an algorithm optimized for efficient compression of Oracle Database files. No extra uncompression steps are required during recovery.

Note:

If you are backing up to tape and your tape device performs its own compression, then you should not use both RMAN backup set compression and the media manager vendor's compression. In most instances you will get better results using the media manager's compression. See the discussion of tuning RMAN's tape backup performance in Chapter 21, "Tuning RMAN Performance".

Example 8-7 backs up the entire database and archived logs to the configured default backup destination (disk or tape), producing compressed backup sets.

Example 8-7 Making Compressed Backups

BACKUP 
  AS COMPRESSED BACKUPSET 
  DATABASE PLUS ARCHIVELOG;

Binary compression creates some performance overhead during backup and restore operations. Binary compression consumes CPU resources, so compressed backups should not be scheduled when CPU usage is already high. However, the following circumstances may warrant paying the performance penalty:

  • You are using disk-based backups when disk space in your flash recovery area or other disk-based backup destination is limited.

  • You are performing your backups to some device over a network when reduced network bandwidth is more important than CPU usage.

  • You are using some archival backup media such as CD or DVD, where reducing backup sizes saves on media costs and archival storage.

See Also:

The AS COMPRESSED BACKUPSET option of the BACKUP command in Oracle Database Backup and Recovery Reference to learn about performance when using binary compression of backup sets

Backing Up Database Files with RMAN

This section contains the following topics:

Making Whole Database Backups with RMAN

You can perform a whole database backup with the database mounted or open. To perform a whole database backup, from the RMAN prompt, use the BACKUP DATABASE command.

You may want to exclude specified tablespaces from a whole database backup. As explained in "Configuring Tablespaces for Exclusion from Whole Database Backups", you can persistently skip tablespaces across RMAN sessions by executing the CONFIGURE EXCLUDE command for each tablespace that you always want to skip. You can override the configured setting with BACKUP ... NOEXCLUDE.

To back up the database:

Start RMAN and connect to a target database and a recovery catalog (if used).

Make sure the database is mounted or open.

Issue the BACKUP DATABASE command at the RMAN prompt.

The simplest form of the command requires no options or parameters, as shown in the following example:

BACKUP DATABASE;

The following example backs up the database, switches the online redo logs, and includes archived logs in the backup:

BACKUP DATABASE PLUS ARCHIVELOG;

By archiving the logs immediately after the backup, you ensure that you have a full set of archived logs through the time of the backup. In this way, you guarantee that you can perform media recovery after restoring this backup.

See Also:

Backing Up Tablespaces and Datafiles with RMAN

You can back up one or more tablespaces with the BACKUP TABLESPACE command or one or more datafiles with the BACKUP DATAFILE command. When you specify tablespaces, RMAN translates the tablespace name internally into a list of datafiles. The database can be mounted or open. Tablespaces can be read/write or read-only.

Note:

Transportable tablespaces do not have to be in read/write mode for backup as in previous releases.

RMAN automatically backs up the control file and the server parameter file (if the instance was started with a server parameter file) when datafile 1 is included in the backup. If control file autobackup is enabled, then RMAN writes the current control file and server parameter file to a separate autobackup piece. Otherwise, RMAN includes these files in the backup set that contains datafile 1.

To back up tablespaces or datafiles:

Start RMAN and connect to a target database and a recovery catalog (if used).

If the database instance is not started, then either mount or open the database.

Run the BACKUP TABLESPACE command or BACKUP DATAFILE command at the RMAN prompt.

The following example backs up the users and tools tablespaces to tape:

BACKUP
  DEVICE TYPE sbt
  TABLESPACE users, tools;

The following example uses an SBT channel to back up datafiles 1 through 4 and a datafile copy stored at /tmp/system01.dbf to tape:

BACKUP 
  DEVICE TYPE sbt 
  DATAFILE 1,2,3,4 
  DATAFILECOPY '/tmp/system01.dbf';

Backing Up Control Files with RMAN

You can back up the control file when the database is mounted or open. RMAN uses a snapshot control file to ensure a read-consistent version. If the CONFIGURE CONTROLFILE AUTOBACKUP command is set to ON (by default it is OFF), then RMAN automatically backs up the control file and server parameter file after every backup and after database structural changes. The control file autobackup contains metadata about the previous backup, which is crucial for disaster recovery.

Note:

You can restore a backup of a control file made on one Data Guard database to any other database in the environment. Primary and standby control file backups are interchangeable. See Oracle Data Guard Concepts and Administration to learn how to use RMAN to restore files on a standby database.

If the autobackup feature is not set, then you must manually back up the control file in one of the following ways:

  • Run BACKUP CURRENT CONTROLFILE

  • Include a backup of the control file within any backup by using the INCLUDE CURRENT CONTROLFILE option of the BACKUP command

  • Back up datafile 1, because RMAN automatically includes the control file and server parameter file in backups of datafile 1

    Note:

    If the control file block size is not the same as the block size for datafile 1, then the control file cannot be written into the same backup set as the datafile. RMAN writes the control file into a backup set by itself if the block size is different. The V$CONTROLFILE.BLOCK_SIZE column indicates the control file block size, whereas the DB_BLOCK_SIZE initialization parameter indicates the block size of datafile 1.

Making a Manual Backup of the Control File

A manual backup of the control file is not the same as a control file autobackup. RMAN makes a control file autobackup after the files specified in the BACKUP command are backed up. Thus, the autobackup—unlike a manual control file backup—contains metadata about the backup that just completed. Also, RMAN can automatically restore autobackups without the use of a recovery catalog.

To make a manual backup, you can either specify INCLUDE CURRENT CONTROLFILE when backing up other files or specify BACKUP CONTROLFILE. You can also back up control files copies on disk by specifying the CONTROLFILECOPY parameter.

To manually back up the control file:

Start RMAN and connect to a target database and a recovery catalog (if used).

Make sure the target database is mounted or open.

Execute the BACKUP command with the desired control file clause.

The following example backs up tablespace users to tape and includes the current control file in the backup:

BACKUP DEVICE TYPE sbt 
  TABLESPACE users 
  INCLUDE CURRENT CONTROLFILE;

The following example backs up the current control file to the default disk device:

BACKUP AS COPY
  CURRENT CONTROLFILE 
  FORMAT '/tmp/control01.ctl';

The following example backs up the control file copy created in the previous example to tape:

BACKUP AS COPY 
  CURRENT CONTROLFILE 
  FORMAT '/tmp/control01.ctl';
BACKUP DEVICE TYPE sbt 
  CONTROLFILECOPY '/tmp/control01.ctl';

If the control file autobackup feature is enabled, then RMAN makes two control file backups in these examples: the explicit backup of the files specified in the BACKUP command and the control file and server parameter file autobackup.

See Also:

Oracle Database Backup and Recovery Reference to learn about the CONFIGURE CONTROLFILE AUTOBACKUP command

Backing Up Server Parameter Files with RMAN

As explained in "Backing Up Control Files with RMAN", RMAN automatically backs up the current server parameter file in certain cases. The BACKUP SPFILE command backs up the parameter file explicitly. The server parameter file that is backed up is the one currently in use by the instance.

To back up the server parameter file:

Start RMAN and connect to a target database and a recovery catalog (if used).

Make sure the target database is mounted or open.

The database must have been started with a server parameter file. If the instance is started with a client-side initialization parameter file, then RMAN issues an error if you execute BACKUP ... SPFILE.

Execute the BACKUP ... SPFILE command.

The following example backs up the server parameter file to tape:

BACKUP DEVICE TYPE sbt SPFILE;

Backing Up a Database in NOARCHIVELOG Mode

The only legal backup of a NOARCHIVELOG database is a closed, consistent backup. This script puts the database into the correct mode for a consistent, whole database backup and then backs up the database. The script assumes that control file autobackup is enabled for the database.

Example 8-8 Backing Up a Database in NOARCHIVELOG Mode

SHUTDOWN IMMEDIATE; 
# Start up the database in case it suffered instance failure or was 
# closed with SHUTDOWN ABORT before starting this script. 
STARTUP FORCE DBA; 
SHUTDOWN IMMEDIATE; 
STARTUP MOUNT;
# this example uses automatic channels to make the backup
BACKUP 
  INCREMENTAL LEVEL 0
  MAXSETSIZE 10M
  DATABASE
  TAG 'BACKUP_1';
# Now that the backup is complete, open the database. 
ALTER DATABASE OPEN; 

You can skip tablespaces, such as read-only tablespaces, but any skipped tablespace that has not been offline or read-only since its last backup is lost if the database has to be restored from a backup.

Backing Up Archived Redo Logs with RMAN

Archived redo logs are the key to successful media recovery. You should back them up regularly.

About Backups of Archived Redo Logs

Several features of RMAN backups are specific to archived redo logs. For example, you can use BACKUP ... DELETE to delete one or all copies of archived redo logs from disk after backing them up to backup sets.

Archived Redo Log Failover

Even if your redo logs are being archived to multiple destinations and you use RMAN to back up archived redo logs, RMAN selects only one copy of the archived redo log file to include in the backup set. Because logs with the same log sequence number are identical, RMAN does not need to include more than one log copy.

The archived redo log failover feature enables RMAN to complete a backup even when some archiving destinations are missing logs or contain logs with corrupt blocks. If at least one log corresponding to a given log sequence and thread is available in the flash recovery area or any of the archiving destinations, then RMAN tries to back it up. If RMAN finds a corrupt block in a log file during backup, it searches other destinations for a copy of that log without corrupt blocks.

For example, assume that you archive logs 121 through 124 to two destinations: /arch1 and /arch2. Table 8-1 shows the archived redo log records in the control file.

Table 8-1 Sample Archived Redo Log Records

Sequence Filename in /arch1 Filename in /arch2

121

/arch1/archive1_121.arc

/arch2/archive1_121.arc

122

/arch1/archive1_122.arc

/arch2/archive1_122.arc

123

/arch1/archive1_123.arc

/arch2/archive1_123.arc

124

/arch1/archive1_124.arc

/arch2/archive1_124.arc


However, unknown to RMAN, a user deletes logs 122 and 124 from the /arch1 directory. Afterward, you run the following backup:

BACKUP ARCHIVELOG
  FROM  SEQUENCE 121 
  UNTIL SEQUENCE 125;

With failover, RMAN completes the backup, using logs 122 and 124 in /arch2.

Online Redo Log Switching

Another important RMAN feature is automatic online redo log switching. To make an open database backup of archived redo logs that includes the most recent online redo log, you can execute the BACKUP command with any of the following clauses:

  • PLUS ARCHIVELOG

  • ARCHIVELOG ALL

  • ARCHIVELOG FROM ...

Before beginning the backup, RMAN switches out of the current redo log group, and archives all online redo logs that have not yet been archived, up to and including the redo log group that was current when the command was issued. This feature ensures that the backup contains all redo generated before the start of the command.

One of the most effective ways of backing up archived redo logs is the BACKUP ... PLUS ARCHIVELOG clause, which causes RMAN to do the following:

Runs the ALTER SYSTEM ARCHIVE LOG CURRENT statement.

Runs BACKUP ARCHIVELOG ALL. If backup optimization is enabled, then RMAN skips logs that it has already backed up to the specified device.

Backs up the rest of the files specified in BACKUP command.

Runs the ALTER SYSTEM ARCHIVE LOG CURRENT statement.

Backs up any remaining archived logs generated during the backup. If backup optimization is not enabled, then RMAN backs up the logs generated in step 1 plus all the logs generated during the backup.

The preceding steps guarantee that datafile backups taken during the command are recoverable to a consistent state. Also, unless the online redo log is archived at the end of the backup, DUPLICATE is not possible with the backup.

Backing Up Archived Redo Log Files

To back up archived logs, use the BACKUP ARCHIVELOG command. Note that if backup optimization is enabled, then RMAN skips backups of archived logs that have already been backed up to the specified device.

To back up archived redo log files:

Start RMAN and connect to a target database and a recovery catalog (if used).

Make sure the target database is mounted or open.

Execute the BACKUP ARCHIVELOG or BACKUP ... PLUS ARCHIVELOG command.

The following example backs up the database and all archived redo logs:

BACKUP DATABASE PLUS ARCHIVELOG;

The following example uses a configured disk or SBT channel to back up one copy of each log sequence number for all archived redo logs:

BACKUP ARCHIVELOG ALL;

You can also specify a range of archived redo logs by time, SCN, or log sequence number, as in the following example:

BACKUP ARCHIVELOG 
  FROM TIME  'SYSDATE-30'
  UNTIL TIME 'SYSDATE-7';

Backing Up Only Archived Redo Logs That Need Backups

You can indicate that RMAN should automatically skip backups of archived redo logs in the following ways:

The BACKUP ... NOT BACKED UP integer TIMES command specifies that RMAN should back up only those archived log files that have not been backed up at least integer times to the specified device. To determine the number of backups for a file, RMAN only considers backups created on the same device type as the current backup.

The BACKED UP clause is a convenient way to back up archived logs to a specified device type. For example, you can specify that RMAN should keep two copies of each archived redo log on tape and skip additional backups.

To back up archived redo logs that need backups:

Start RMAN and connect to a target database and a recovery catalog (if used).

Make sure the target database is mounted or open.

Make sure that appropriate channels are configured for the backup.

Execute the BACKUP ARCHIVELOG command with the NOT BACKED UP clause.

BACKUP ARCHIVELOG ALL NOT BACKED UP 2 TIMES;

See Also:

"Using Backup Optimization to Skip Files" for scenarios using NOT BACKED UP

Deleting Archived Redo Logs After Backups

The BACKUP ARCHIVELOG ... DELETE INPUT command deletes archived log files after they are backed up. This command eliminates the separate step of manually deleting archived redo logs.

With DELETE INPUT, RMAN deletes only the specific copy of the archived log chosen for the backup set. With DELETE ALL INPUT, RMAN deletes each backed-up archived redo log file from all log archiving destinations.

As explained in "Configuring an Archived Redo Log Deletion Policy", the BACKUP ... DELETE INPUT and DELETE ARCHIVELOG commands obey the archived redo log deletion policy for logs in all archiving locations. For example, if you specify that logs should only be deleted when backed up at least twice to tape, then BACKUP ... DELETE honors this policy.

For the following procedure, assume that you archive to /arc_dest1, /arc_dest2, and the flash recovery area.

To delete archived redo logs after a backup:

Start RMAN and connect to a target database and a recovery catalog (if used).

Make sure that the target database is mounted or open.

Run the BACKUP command with the DELETE INPUT clause.

Assume that you run the following BACKUP command:

BACKUP DEVICE TYPE sbt 
  ARCHIVELOG ALL 
    DELETE ALL INPUT;

In this case, RMAN backs up only one copy of each log sequence number in these archiving locations. RMAN does not delete any logs from the flash recovery area, but it deletes all copies of any log that it backed up from the other archiving destinations. The logs in the flash recovery area that are eligible for deletion will be automatically removed by the database when space is needed.

If you had specified DELETE INPUT rather than DELETE ALL INPUT, then RMAN would only delete the specific archived redo log files that it backed up. For example, RMAN would delete the logs in /arc_dest1 if these files were used as the source of the backup, but leave the contents of the /arc_dest2 intact.

See Also:

Making and Updating Incremental Backups

As explained in "Incremental Backups", an incremental backup copies only datafile blocks that have changed since a specified previous backup. An incremental backups is either a cumulative incremental backup or differential incremental backup.

Although the content of the backups are the same, BACKUP DATABASE and BACKUP INCREMENTAL LEVEL 0 DATABASE are different. A full backup is not usable as part of an incremental strategy, whereas a level 0 incremental backup is the basis of an incremental strategy. No RMAN command can change a full backup into a level 0.

As with full backups, RMAN can make incremental backups of an ARCHIVELOG mode database that is open or mounted. If the database is in NOARCHIVELOG mode, then RMAN can only make incremental backups after a consistent shutdown.

Purpose of Incremental Backups

The primary reasons for making incremental backups part of your strategy are:

  • Faster daily backups if block change tracking is enabled (see "Using Block Change Tracking to Improve Incremental Backup Performance").

  • Ability to roll forward datafile image copies, thereby reducing recovery time and avoiding repeated full backups.

  • Less bandwidth consumption when backing up over a network

  • Improved performance when the aggregate tape bandwidth for tape write I/Os is much less than the aggregate disk bandwidth for disk read I/Os.

  • Possibility of recovering changes to objects created with the NOLOGGING option.

    For example, direct load inserts do not create redo log entries, so their changes cannot be reproduced with media recovery. Direct load inserts do change data blocks, however, and so these blocks are captured by incremental backups.

  • Synchronize a physical standby database with the primary database. You can use the RMAN BACKUP INCREMENTAL FROM SCN command to create a backup on the primary database that starts at the current SCN of the standby, which you can then use to roll forward the standby database. See Oracle Data Guard Concepts and Administration to learn how to apply incremental backups to a standby database.

See Also:

Oracle Database Administrator's Guide for more information about NOLOGGING mode

Planning an Incremental Backup Strategy

Choose a backup strategy according to an acceptable MTTR (mean time to recover). For example, you can implement a three-level backup scheme so that a full or level 0 backup is taken monthly, a cumulative level 1 is taken weekly, and a differential level 1 is taken daily. In this strategy, you never have to apply more than a day of redo for complete recovery.

When deciding how often to take full or level 0 backups, a good rule of thumb is to take a new level 0 backup whenever 20% or more of the data has changed. If the rate of change to your database is predictable, then you can observe the size of your incremental backups to determine when a new level 0 is appropriate. The following SQL query determines the number of blocks written to an incremental level 1 backup of each datafile with at least 20% of its blocks backed up:

SELECT   FILE#, INCREMENTAL_LEVEL, COMPLETION_TIME, 
         BLOCKS, DATAFILE_BLOCKS 
FROM     V$BACKUP_DATAFILE 
WHERE    INCREMENTAL_LEVEL > 0 
AND      BLOCKS / DATAFILE_BLOCKS > .2
ORDER BY COMPLETION_TIME;

Compare the number of blocks in level 1 backups to a level 0 backup. For example, if you only create level 1 cumulative backups, then take a new level 0 backup when the most recent level 1 backup is about half of the size of the level 0 backup.

An effective way to conserve disk space is to make incremental backups to disk, and then offload the backups to tape with BACKUP AS BACKUPSET. Incremental backups are generally smaller than full backups, which limits the space required to store them until they are moved to tape. When the incremental backups on disk are backed up to tape, the tape is more likely to stream because all blocks of the incremental backup are copied to tape. There is no possibility of delay due to time required for RMAN to locate changed blocks in the datafiles.

Another strategy is to use incrementally updated backups as explained in "Incrementally Updating Backups". In this strategy, you create an image copy of each datafile, then periodically roll forward this copy by making and then applying a level 1 incremental backup. In this way you avoid the overhead of making repeated full image copies of your datafiles, but enjoy all of the advantages.

In a Data Guard environment, you can offload incremental backups to a physical standby database. Incremental backups of a standby and primary database are interchangeable. Thus, you can apply an incremental backup of a standby database to a primary database, or apply an incremental backup of a primary database to a standby database. You can also enable block change tracking at a standby database, regardless of whether it is enabled at any other database in the Data Guard environment. In this way, RMAN automatically optimizes incremental backups of the standby database.

See Also:

Oracle Data Guard Concepts and Administration to learn how to back up a standby database with RMAN

Making Incremental Backups

After starting RMAN, run the BACKUP INCREMENTAL command at the RMAN prompt. By default incremental backups are differential.

To make an incremental backup:

Start RMAN and connect to a target database and a recovery catalog (if used).

Make sure the target database is mounted or open.

Execute the BACKUP INCREMENTAL command with the desired options.

Use the LEVEL parameter to indicate the incremental level.The following example makes a level 0 incremental database backup.

BACKUP
  INCREMENTAL LEVEL 0
  DATABASE;

The following example makes a differential incremental backup at level 1 of the SYSTEM and tools tablespaces. It will only back up those data blocks changed since the most recent level 1 or level 0 backup.

BACKUP
  INCREMENTAL LEVEL 1
  TABLESPACE SYSTEM, tools;

The following example makes a cumulative incremental backup at level 1 of the tablespace users, backing up all blocks changed since the most recent level 0 backup.

BACKUP
  INCREMENTAL LEVEL 1 CUMULATIVE
  TABLESPACE users;

Making Incremental Backups of a VSS Snapshot

You can use the Volume Shadow Copy Service (VSS) in conjunction with the Oracle VSS writer to make a shadow copy or snapshot of files in an Oracle Database. You must use a third-party backup program other than RMAN to make VSS snapshots with the Oracle VSS writer. In this case, the flash recovery area automates management of files that are already backed up in a VSS snapshot and deletes them as needed.

You can use the BACKUP INCREMENTAL LEVEL 1 ... FROM SCN command in RMAN to create incremental backups in the flash recovery area. Thus, you can use this command to create an incremental level 1 backup of a VSS shadow copy. RMAN can apply incremental backups during recovery transparently.

See Also:

Oracle Database Platform Guide for Microsoft Windows to learn how to make VSS backups with RMAN

Incrementally Updating Backups

By incrementally updating backups, you can avoid the overhead of making full image copy backups of datafiles, while also minimizing time required for media recovery of your database. For example, if you run a daily backup script, then you never have more than one day of redo to apply for media recovery.

To incrementally update datafile backups:

Make a full image copy backup of a datafile.

At regular intervals (such as daily), make level 1 incremental backups of the datafile and apply them to the image copy backup.

This technique rolls forward the backup to the time when the level 1 incremental was made. RMAN can restore this incrementally updated backup and apply changes from the redo log. The result is the same as restoring a datafile backup taken at the SCN of the most recently applied incremental level 1 backup.

Note:

If you run the RECOVER COPY command daily, then a continuously updated image copy cannot satisfy a recovery window of more than one day. The incrementally updated backup feature is an optimization for fast media recovery.

Incrementally Updating Backups: Basic Example

To create incremental backups for use in an incrementally updated backups strategy, use the BACKUP ... FOR RECOVER OF COPY WITH TAG form of the BACKUP command. The command is best understood in the context of a sample script that implements the strategy.

This script in Example 8-9, run on a regular basis, is all that is required to implement a strategy based on incrementally updated backups.

Example 8-9 Basic Incremental Update Script

RUN
{
  RECOVER COPY OF DATABASE 
    WITH TAG 'incr_update';
  BACKUP 
    INCREMENTAL LEVEL 1
    FOR RECOVER OF COPY WITH TAG 'incr_update'
    DATABASE;
}

To understand the script and the strategy, it is necessary to understand the effects of these two commands when no datafile copies or incremental backups exist. Note two important features:

  • The BACKUP command in Example 8-9 does not always create a level 1 incremental backup.

  • The RECOVER command in Example 8-9 causes RMAN to apply any available incremental level 1 backups to a set of datafile copies with the specified tag.

The effect of the script is shown in the following table. The columns show the effects of the first run of the script, the second run of the script, and then the third and all subsequent run of the script.

Table 8-2 Effect of Script When Run Multiple Times

Command Run 1 Run 2 Run 3 Onward

RECOVER

Because there is no incremental backup or datafile copy, the command generates a message (but not an error). That is, the command has no effect.

A datafile copy now exists, but no incremental level 1 backup exists with which to recover it. Thus, the RECOVER command has no effect.

A datafile copy and level 1 incremental exist from the previous run. The level 1 incremental is applied to the datafile copy, bringing the copy up to the checkpoint SCN of the level 1 incremental.

BACKUP

Because no level 0 image copy backup exists, the command creates an image copy backup of the datafile on disk with the specified tag. In other words, the script creates the image copy needed to begin the cycle of incremental updates.

Note: If the script sets DEVICE TYPE sbt, then the first run creates the copy on disk, and not on tape. Subsequent runs make level 1 backups on tape.

The command makes an incremental level 1 backup containing block changes for the previous day.

The command makes an incremental level 1 backup containing block changes for the previous day.


Note also the following details about how Example 8-9 works:

  • Each time a datafile is added to the database, an image copy of the new datafile is created the next time the script runs. The next run makes the first level 1 incremental for the added datafile. On all subsequent runs the new datafile is processed like any other datafile.

  • You must use tags to identify the incremental level 0 datafile copies created for use in this strategy so that they do not interfere with other backup strategies you implement. If you use multiple incremental backup strategies, then RMAN cannot unambiguously create incremental level 1 backups unless you tag level 0 backups.

    The incremental level 1 backups to apply to those image copies are selected based upon the checkpoint SCNs of the image copy datafiles and the available incremental level 1 backups. The tag used on the image copy being recovered is not a factor in the selection of the incremental level backups.

In practice, you would schedule the script in Example 8-9 to run after each day, possibly at midnight. After the third run of the script, the following files would be available for a point-in-time recovery:

  • An image copy of the database, as of the checkpoint SCN of the preceding run of the script, 24 hours earlier

  • An incremental backup for the changes after the checkpoint SCN of preceding run

  • Archived redo logs including all changes between the checkpoint SCN of the image copy and the current time

If at some point during the following 24 hours you need to restore and recover your database, then you can restore the datafiles from the incrementally updated datafile copies. You can then apply changes from the most recent incremental level 1 and the redo logs to reach the desired SCN. At most, you have 24 hours of redo to apply, which limits how long point-in-time recovery will take.

See Also:

Oracle Database 2 Day DBA to see how this technique is used in the Oracle-suggested backup strategy in Enterprise Manager

Incrementally Updated Backups: Advanced Example

You can extend the basic script in Example 8-9 to provide fast recoverability to a window greater than 24 hours. Example 8-10 shows how to maintain a window of seven days by specifying the beginning time of your window of recoverability in the RECOVER command.

Example 8-10 Advanced Incremental Update Script

RUN
{
  RECOVER COPY OF DATABASE 
    WITH TAG 'incr_update' 
    UNTIL TIME 'SYSDATE - 7';
  BACKUP
    INCREMENTAL LEVEL 1 
    FOR RECOVER OF COPY WITH TAG 'incr_update'
    DATABASE;
}

The effect of the script is shown in the following table. The columns show the effects of the first run of the script, the second through seventh run of the scripts, and then each subsequent run of the script.

Table 8-3 Effect of Script When Run Multiple Times


Run 1 Run 2-7 Run 8 Onward

RECOVER command

Does nothing because no backup exists to recover

Does nothing because UNTIL TIME SYSDATE-7 specifies a time in the future

Applies the level 1 incremental backup made 7 days ago to the existing database copy

BACKUP command

Makes an incremental level 0 copy because no level 0 copy exists

Makes an incremental level 1 backup containing block changes for the previous day

Makes an incremental backup with the changes from the previous day


As with the basic script in Example 8-9, you have fast recoverability to any point in time between the SCN of the datafile copies and the present. RMAN can use both block changes from the incremental backups and individual changes from the redo logs. Because you have the daily level 1 incrementals, you still never need to apply more than one day of redo.

See Also:

Oracle Database Backup and Recovery Reference to learn about the RECOVER command

Using Block Change Tracking to Improve Incremental Backup Performance

The block change tracking feature for incremental backups improves backup performance by recording changed blocks for each datafile.

About Block Change Tracking

If block change tracking is enabled on a primary or standby database, then RMAN uses a block change tracking file to identify changed blocks for incremental backups. By reading this small bitmap file to determine which blocks changed, RMAN avoids having to scan every block in the datafile that it is backing up.

Block change tracking is disabled by default. Nevertheless, the benefits of avoiding full datafile scans during backup are considerable, especially if only a small percentage of data blocks are changed between backups. If your backup strategy involves incremental backups, then block change tracking is recommended. Block change tracking in no way changes the commands used to perform incremental backups. The change tracking files themselves generally require little maintenance after initial configuration.

Space Management in the Block Change Tracking File

The change tracking file maintains bitmaps that mark changes in the datafiles between backups. The database performs a bitmap switch before each backup. Oracle Database automatically manages space in the change tracking file to retain block change data that covers the 8 most recent backups. After the maximum of 8 bitmaps is reached, the most recent bitmap is overwritten by the bitmap that tracks the current changes.

The first level 0 incremental backup scans the entire datafile. Subsequent incremental backups use the block change tracking file to scan only the blocks that have been marked as changed since the last backup. An incremental backup can be optimized only when it is based on a parent backup that was made after the start of the oldest bitmap in the block change tracking file.

Consider the 8-bitmap limit when developing your incremental backup strategy. For example, if you make a level 0 database backup followed by 7 differential incremental backups, then the block change tracking file now includes 8 bitmaps. If you then make a cumulative level 1 incremental backup, then RMAN cannot optimize the backup because the bitmap corresponding to the parent level 0 backup is overwritten with the bitmap that tracks the current changes.

Location of the Block Change Tracking File

One block change tracking file is created for the whole database. By default, the change tracking file is created as an Oracle-managed file in the destination specified by the DB_CREATE_FILE_DEST initialization parameter. You can also specify the name of the block change tracking file by placing it in any location you choose. You can use a raw device (that is, a disk without a file system) as a block changing file, but be sure that the device is sufficiently large.

Note:

In an Oracle RAC environment, the change tracking file must be located on shared storage accessible from all nodes in the cluster.

RMAN does not support backup and recovery of the change tracking file. The database resets the change tracking file when it determines that the change tracking file is invalid. If you restore and recover the whole database or a subset, then the database clears the block change tracking file and starts tracking changes again. After you make a level 0 incremental backup, the next incremental backup is able to use change tracking data.

Size of the Block Change Tracking File

The size of the block change tracking file is proportional to the size of the database and the number of enabled threads of redo. The size of the block change tracking file can increase and decrease as the database changes. The size is not related to the frequency of updates to the database.

Typically, the space required for block change tracking is approximately 1/30,000 the size of the data blocks to be tracked. The following factors that may cause the file to be larger than this estimate suggests:

  • To avoid the overhead of allocating space as your database grows, the block change tracking file size starts at 10 MB. New space is allocated in 10 MB increments. Thus, for any database up to approximately 300 GB, the file size is no smaller than 10 MB, for up to approximately 600 GB the file size is no smaller than 20 MB, and so on.

  • For each datafile, a minimum of 320 KB of space is allocated in the block change tracking file, regardless of the size of the datafile. Thus, if you have a large number of relatively small datafiles, the change tracking file is larger than for databases with a smaller number of larger datafiles containing the same data.

Enabling and Disabling Block Change Tracking

You can enable block change tracking when the database is either open or mounted. This section assumes that you intend to create the block change tracking file as an Oracle-managed file in the database area, which is where the database maintains active database files such as datafiles, control files, and online redo log files. See "Overview of the Flash Recovery Area" to learn about the database area and flash recovery area.

To enable block change tracking:

Start SQL*Plus and connect to a target database with administrator privileges.

Make sure that the DB_CREATE_FILE_DEST initialization parameter is set.

SHOW PARAMETER DB_CREATE_FILE_DEST

If the parameter is not set, and if the database is open, then you can set the parameter with the following form of the ALTER SYSTEM statement:

ALTER SYSTEM SET 
  DB_CREATE_FILE_DEST = '/disk1/bct/'
  SCOPE=BOTH SID='*';

Enable block change tracking.

Execute the following ALTER DATABASE statement:

ALTER DATABASE ENABLE BLOCK CHANGE TRACKING;

You can also create the change tracking file in a location you choose yourself by using the following form of SQL statement:

ALTER DATABASE ENABLE BLOCK CHANGE TRACKING 
  USING FILE '/mydir/rman_change_track.f' REUSE;

The REUSE option tells Oracle Database to overwrite any existing block change tracking file with the specified name.

Disabling Block Change Tracking

This section assumes that the block change tracking feature is currently enabled. When you disable block change tracking, the database removes the block change tracking file from the operating system.

To disable block change tracking:

Start SQL*Plus and connect to a target database with administrator privileges.

Ensure that the target database is mounted or open.

Disable block change tracking.

Execute the following ALTER DATABASE statement:

ALTER DATABASE DISABLE BLOCK CHANGE TRACKING;

Checking Whether Change Tracking is Enabled

You can query the V$BLOCK_CHANGE_TRACKING view to determine whether change tracking is enabled, and if it is, the filename of the block change tracking file.

To determine whether change tracking is enabled:

  • Enter the following query in SQL*Plus (sample output included):

    COL STATUS   FORMAT A8
    COL FILENAME FORMAT A60
     
    SELECT STATUS, FILENAME
    FROM   V$BLOCK_CHANGE_TRACKING;
    
    STATUS   FILENAME
    -------- ------------------------------------------------------------
    ENABLED  /disk1/bct/RDBMS/changetracking/o1_mf_2f71np5j_.chg
    

Changing the Location of the Block Change Tracking File

To move the change tracking file, use the ALTER DATABASE RENAME FILE statement. The database must be mounted. The statement updates the control file to refer to the new location and preserves the contents of the change tracking file. If you cannot shut down the database, then you can disable and enable block change tracking. In this case, you lose the contents of the existing block change tracking file.

To change the location of the change tracking file:

Start SQL*Plus and connect to a target database.

If necessary, determine the current name of the change tracking file:

SQL> SELECT FILENAME FROM V$BLOCK_CHANGE_TRACKING;

If possible, shut down the database. For example:

SQL> SHUTDOWN IMMEDIATE

If you shut down the database, then skip to the next step. If you choose not to shut down the database, then execute the following SQL statements and skip all remaining steps:

SQL> ALTER DATABASE DISABLE BLOCK CHANGE TRACKING;
SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE 'new_location';

In this case you lose the contents of the block change tracking file. Until the next time you complete a level 0 incremental backup, RMAN must scan the entire file.

Using host operating system commands, move the change tracking file to its new location.

Mount the database and move the change tracking file to a location that has more space. For example:

ALTER DATABASE RENAME FILE
   '/disk1/bct/RDBMS/changetracking/o1_mf_2f71np5j_.chg' TO 
   '/disk2/bct/RDBMS/changetracking/o1_mf_2f71np5j_.chg';

This statement changes the location of the change tracking file while preserving its contents.

Open the database:

SQL> ALTER DATABASE OPEN;

See Also:

Oracle Database SQL Language Reference to learn about the ALTER DATABASE statement and the ALTER SYSTEM statement

Making Database Backups for Long-Term Storage

This section explains the basic concepts and tasks involved in making backups for long-term storage.

Purpose of Archival Backups

You can use BACKUP ... KEEP to create a backup that is both all-inclusive and exempt from the backup retention policy. The backup is all-inclusive because every file needed to restore and recover the database is backed up to a single disk or tape location. The KEEP option also specifies that the backup should be exempt from the retention policy either forever or for a specified period of time. The general name for a backup created with BACKUP ... KEEP is an archival backup.

As explained in "Data Preservation", one purpose of a backup and recovery strategy is to preserve data. You can use BACKUP ... KEEP to retain a database backup for longer than the time dictated by the retention policy. For example, you can back up the database on the first day of every year to satisfy a regulatory requirement and store the media offsite. Years after you make the archival backup, you could restore and recover it to query the data as it appeared at the time of the backup.

Another purpose of an archival backup is to create a backup that you want to restore for testing purposes and then delete. For example, you can back up the database, restore the database in a test environment, and then discard the archival backup after the test database is operational. A related purpose is to create a self-contained backup that you can delete after transferring it to another user or host. For example, another user might want a copy of the database for reporting or testing.

Basic Concepts of Archival Backups

You can exempt a backup from the retention policy by using the KEEP option with the BACKUP command. You can also use the KEEP and NOKEEP options of the CHANGE command to change the status of an existing backup. Backups with KEEP attributes are valid backups that can be recovered like any other backups.

You can specify an end date for an archival backup with the KEEP UNTIL TIME clause, or specify that the backup should be kept FOREVER. If you specify UNTIL, then RMAN marks the backup as obsolete when the UNTIL time has passed, regardless of any configured retention policy. For example, if you specify KEEP UNTIL TIME '01-JAN-08', then the backup is obsolete one second after midnight on January 1. If you specify an UNTIL TIME of 9:00 p.m, then the backup is obsolete at 9:01 p.m.

When you specify KEEP on the BACKUP command, RMAN generates multiple backup sets. Note the following characteristics of the BACKUP ... KEEP command:

  • It automatically backs up the datafiles, control file (even if the control file autobackup is disabled), and the server parameter file.

  • It automatically generates an archived redo log backup to ensure that the database backup can be recovered to a consistent state.

  • If the FORMAT, POOL, or TAG parameters are specified, then they are used for all backups. For this reason, the FORMAT string must allow for the creation of multiple backup pieces. Specifying the %U substitution variable is the easiest way to meet this requirement.

  • It supports an optional RESTORE POINT clause that creates a normal restore point, which is a label for an SCN to which the backup must be recovered to be made consistent. The SCN is captured just after the datafile backups complete. RMAN resynchronizes restore points with the recovery catalog and maintains the restore points as long as the backup exists. "Listing Restore Points" explains how to display restore points.

See Also:

Oracle Database Backup and Recovery Reference for CHANGE syntax and Oracle Database Backup and Recovery Reference for BACKUP ... KEEP syntax

Making an Archival Backup for Long-Term Storage

This section describes how to make a database backup for archival purposes. Typically, you make an archival backup to tape. Because your data protection backups will most likely be on a set of tapes that remain accessible and are recycled, it is advisable to earmark a set of tapes for the archival backup. You can write the archival backup to this special set of tapes and then place them in offsite storage.

This section explains the standard technique for creating an archival backup. You can vary the procedure to create a stored script or shell script that you can update dynamically. When you run the script, you can dynamically set the name of the restore point, backup format, and so on.

See Also:

Making an Archival Backup

This scenario makes a long-term archival backup with a backup tag of QUARTERLY and assigns it to a special family of Oracle Secure Backup tapes reserved for long-term storage. Note the following features of this example:

  • The FOREVER keyword indicates that this backup is never eligible for deletion by the backup retention policy.

  • The BACKUP command creates the restore point named FY06Q4 to match the SCN at which this backup will be consistent.

To make a long-term archival backup:

Start RMAN and connect to a target database and recovery catalog.

The target database can be open or mounted. A recovery catalog is required for KEEP FOREVER, but is not required for any other KEEP option.

Run BACKUP ... KEEP to make the backup.

The following example generates a datafile and archived log backup and creates a normal restore point. Note that the specified restore point must not already exist.

The log backup contains just those archived logs needed to restore this backup to a consistent state. The database performs a online redo log switch to archive the redo that is in the current online logs and is necessary to make this new backup consistent. The control file autobackup has a copy of the restore point, so it can be referenced as soon as the control file is restored.

RUN
{
  ALLOCATE CHANNEL c1 
    DEVICE TYPE sbt
    PARMS 'ENV=(OB_MEDIA_FAMILY=archival_backup)';
  BACKUP DATABASE
    TAG quarterly
    KEEP FOREVER
    RESTORE POINT FY06Q4;
}

The following variation keeps the backup for 365 days instead of keeping it forever. After a year has passed, the backup becomes obsolete regardless of the backup retention policy settings.

RUN
{
  ALLOCATE CHANNEL c1 DEVICE TYPE sbt
    PARMS 'ENV=(OB_MEDIA_FAMILY=archival_backup)';
  BACKUP DATABASE
    TAG quarterly
    KEEP UNTIL TIME 'SYSDATE+365'
    RESTORE POINT FY06Q4;
}

See Also:

"About Restore Points and Flashback Database" to learn about restore points

Making a Temporary Archival Backup

One purpose of an archival backup is for creating a test database. The technique for making a test database is essentially the same as the technique described in "Making an Archival Backup for Long-Term Storage". The difference is that you intend to delete the backup soon after creating it.

You can specify the temporary status of the backup with the BACKUP ... KEEP UNTIL parameter. Assume that you want to make a backup and then restore it to a new host the same day. In this case, you can specify KEEP UNTIL TIME SYSDATE+1 to indicate that RMAN should override the retention policy for this backup for only one day. After one day, the backup becomes obsolete, regardless of any configured backup retention policy.

The command in Example 8-11 makes an archival backup on a temporary disk with the tag TESTDB. The example creates a normal restore point, which is a label for the time to which the backup should be recovered. RMAN only backs up the archived redo logs if the database is open during the backup. Archived logs are not needed for offline backups and so are not backed up.

Example 8-11 Creating a Temporary Archival Backup

BACKUP DATABASE
  FORMAT '/disk1/oraclebck/%U' 
  TAG TESTDB 
  KEEP UNTIL TIME 'SYSDATE+1' 
  RESTORE POINT TESTDB06;

The recommended technique for restoring an archival backup is to use the DUPLICATE command. Refer to "Using DUPLICATE to Restore an Archival Backup".

Backing Up RMAN Backups

This section explains how to back up backup sets and image copies.

About Backups of Backups

You can use the BACKUP BACKUPSET command to back up backup sets produced by other backup jobs. You can also use BACKUP RECOVERY AREA to back up recovery files created in the current and all previous flash recovery area destinations. Recovery files are full and incremental backup sets, control file autobackups, datafile copies, and archived redo logs. Only SBT backups are supported for BACKUP RECOVERY AREA.

The preceding commands are especially useful in the following scenarios:

  • Ensuring that all backups exist both on disk and on tape.

  • Moving backups from disk to tape and then freeing space on disk. This task is especially important when the database uses a flash recovery area so that the space can be reused as needed.

    Note:

    You cannot duplex backups when running BACKUP BACKUPSET. RMAN always makes one and only one copy on the specified media when performing BACKUP BACKUPSET.

You can also the BACKUP COPY OF command to back up image copies of datafiles, control files, and archived redo logs. The output of this command can be either backup sets or image copies, so you can generate backup sets from image copies. This form of backup is used to back up a database backup created as image copies on disk to tape.

Multiple Copies of Backup Sets

BACKUP BACKUPSET creates additional copies of backup pieces in a backup set, but does not create a new backup set. Thus, BACKUP BACKUPSET is similar to using the DUPLEX or MAXCOPIES option of BACKUP (see "Duplexing Backup Sets"). The extra copy of a backup set created by BACKUP BACKUPSET is not a new backup set, just as copies of a backup set produced by other forms of the BACKUP command are not separate backup sets.

Effect of a Backup Retention Policy on Backups of Backups

For the purposes of a backup retention policy based on redundancy, a backup set is counted as one instance of a backup. This statement is true even if there are multiple copies of the backup pieces that make up backup set, such as when a backup set has been backed up from disk to tape.

For the purposes of a recovery window retention policy, either all of the copies of a backup set are obsolete, or none of them are. This point is easiest to grasp when viewing the output of the LIST and REPORT commands.

To view the effect of a backup retention policy on backups of backups:

  1. Back up a datafile.

    The following example backs up datafile 5:

    BACKUP AS BACKUPSET DATAFILE 5;
    

    Run the LIST command for the datafile backup in the preceding step.

    For example, run the following command (sample output included).

    
    LIST BACKUP OF DATAFILE 5 SUMMARY;
     
    List of Backups
    ===============
    Key     TY LV S Device Type Completion Time #Pieces #Copies Compressed Tag
    ------- -- -- - ----------- --------------- ------- ------- ---------- ---
    18      B  F  A DISK        04-AUG-07       1       1       NO         TAG20070804T160 134
    

    Use the backup set key from the previous step to back up the backup set.

    For example, enter the following command:

    BACKUP BACKUPSET 18;
    

    Run the same LIST command that you ran in step 2.

    For example, run the following command (sample output included).

    
    LIST BACKUP OF DATAFILE 5 SUMMARY;
     
    List of Backups
    ===============
    Key     TY LV S Device Type Completion Time #Pieces #Copies Compressed Tag
    ------- -- -- - ----------- --------------- ------- ------- ---------- ---
    18      B  F  A DISK        04-AUG-07       1       2       NO         TAG20070804T160 134
    

    Only one backup set is shown in this output, but there are now two copies of it.

    Generate a report to see the effect of these copies under a redundancy-based backup retention policy.

    For example, issue the following command:

    REPORT OBSOLETE REDUNDANCY 1;
     
    

    None of the copies is reported as obsolete because both copies of the backup set have the same values for set_stamp and set_count.

    Generate a report to see the effect of these copies under a recovery window-based backup retention policy.

    For example, issue the following command:

    REPORT OBSOLETE RECOVERY WINDOW 1 DAY;
     
    

    None of the copies of the backup set is reported as obsolete or based on the CHECKPOINT_CHANGE# of this backup set, with respect to the current time and the availability of other backups.

Backing Up Backup Sets with RMAN

This section explains how to use the BACKUP BACKUPSET command to copy backup sets from disk to tape. The procedure assumes that you have already configured an SBT device as your default device.

To back up backup sets from disk to tape:

If you are backing up a subset of available backup sets, then execute the LIST BACKUPSET command to obtain their primary keys.

The following example lists the backup sets in summary form:

RMAN> LIST BACKUPSET SUMMARY;

List of Backups
===============
Key TY LV S Device Type Completion Time #Pieces #Copies Comp Tag
--- -- -- - ----------- --------------- ------- ------- ---- ---
1   B  F  A DISK        28-MAY-07       1       1       NO   TAG20070528T132432
2   B  F  A DISK        29-MAY-07       1       1       NO   TAG20070529T132433
3   B  F  A DISK        30-MAY-07       1       1       NO   TAG20070530T132434

The following example lists details about backup set 3 in verbose form:

RMAN> LIST BACKUPSET 3;

List of Backup Sets
===================

BS Key  Type LV Size       Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
3       Full    8.33M      DISK        00:00:01     30-MAY-07
        BP Key: 3   Status: AVAILABLE  Compressed: NO  Tag: TAG20070530T132434
        Piece Name: /disk1/oracle/dbs/c-35764265-20070530-02
  Control File Included: Ckp SCN: 397221       Ckp time: 30-MAY-07
  SPFILE Included: Modification time: 30-MAY-07
  SPFILE db_unique_name: PROD

Execute the BACKUP BACKUPSET command.

The following example backs up all disk backup sets to tape and then deletes the input disk backups:

BACKUP BACKUPSET ALL
  DELETE INPUT;

The following example backs up only the backup sets with the primary key 1 and 2 to tape and then deletes the input disk backups:

BACKUP BACKUPSET 1,2
  DELETE INPUT;

Optionally, execute the LIST command to see a listing of backup sets and pieces.

The output lists all copies, including backup piece copies created by BACKUP BACKUPSET.

Backing Up Image Copy Backups with RMAN

This section explains how to use the BACKUP command to back up image copies to tape. It is assumed that you have configured an SBT device as your default device.

Note that when backing up image copies that have multiple copies of the datafiles, specifying tags for the backups makes it easier to identify the input image copy. All image copies of datafiles have tags. The tag of an image copy is inherited by default when the image copy is backed up as a new image copy.

To back up image copies from disk to tape:

Issue the BACKUP ... COPY OF or BACKUP DATAFILECOPY command.

The following example backs up datafile copies that have the tag DBCopy:

BACKUP DATAFILE COPY FROM TAG monDBCopy;

The following example backs up the latest image copies of a database to tape, assigns the tag QUARTERLY_BACKUP, and deletes the input disk backups:

BACKUP DEVICE TYPE sbt
  TAG "quarterly_backup"
  COPY OF DATABASE 
  DELETE INPUT;

Optionally, issue the LIST command to see a listing of backup sets. The output lists all copies, including backup piece copies created by BACKUP BACKUPSET.