6 Configuring the RMAN Environment: Advanced Topics

In addition to configuring parameters that apply to all channels of a particular type, you can also configure parameters that apply to one specific channel. Run the CONFIGURE CHANNEL n command (where n is a positive integer less than 255) to configure a specific channel.

When manually numbering channels, you must specify one or more channel options (for example, MAXPIECESIZE or FORMAT) for each channel. When you use that specific numbered channel in a backup, the configured settings for that channel are used instead of the configured generic channel settings.

Configure specific channels by number when it is necessary to control the parameters set for each channel separately. This technique is necessary in the following situations:

• When running an Oracle Real Application Clusters (Oracle RAC) database in which individual nodes do not have access to the full set of backups. Each channel must be configured with a node-specific connect string so that all backups are accessible by at least one channel.

• When using a media manager that requires different PARMS settings on each channel.

In tape backups, it is possible for a multiplexed backup set to span multiple tapes, which means that blocks from each data file in the backup set are written to multiple tapes. If one tape of a multivolume backup set fails, then you lose the data on all the tapes rather than just one. If a backup is not a multisection backup, then a backup set always includes a whole data file rather than a partial data file. You can use MAXSETSIZE to specify that each backup set fits on one tape rather than spanning multiple tapes.

The CONFIGURE MAXSETSIZE command limits the size of backup sets created on a channel. This CONFIGURE setting applies to any channel, whether manually allocated or configured, when the BACKUP command is used to create backup sets. The default value is given in bytes and is rounded down to the lowest kilobyte value.

The value set by the CONFIGURE MAXSETSIZE command is a default for the given channel. You can override the configured MAXSETSIZE value by specifying a MAXSETSIZE option for an individual BACKUP command.

Assume that you issue the following commands at the RMAN prompt:

CONFIGURE DEFAULT DEVICE TYPE TO sbt;
CONFIGURE CHANNEL DEVICE TYPE sbt PARMS 'ENV=(OB_MEDIA_FAMILY=first_pool)'; 
CONFIGURE MAXSETSIZE TO 7500K;
BACKUP TABLESPACE users;
BACKUP TABLESPACE tools MAXSETSIZE 5G;

The results are as follows:

• The backup of the users tablespace uses the configured SBT channel and the configured default MAXSETSIZE setting of 7500K.

• The backup of the tools tablespace uses the MAXSETSIZE setting of 5G specified in the BACKUP command.

Backup piece size is an issue when it exceeds the maximum file size permitted by the file system or media management software. You can use the MAXPIECESIZE parameter of the CONFIGURE CHANNEL or ALLOCATE CHANNEL command to limit the size of backup pieces.

For example, to limit the backup piece size to 2 gigabytes or less, you can configure the automatic DISK channel as follows and then run BACKUP DATABASE:

CONFIGURE CHANNEL DEVICE TYPE DISK MAXPIECESIZE 2G;
BACKUP DATABASE;

You can use the CONFIGURE ... BACKUP COPIES command to specify how many copies of each backup piece are created on the specified device type for the specified type of file. This type of backup is known as a duplexed backup set. The CONFIGURE settings for duplexing only affect backups of data files, control files, and archived logs into backup sets, and do not affect image copies.

RMAN can duplex backups to either disk or tape, but cannot duplex backups to tape and disk simultaneously. When backing up to tape, ensure that the number of copies does not exceed the number of available tape devices. The following examples show possible duplexing configurations:

# Makes 2 disk copies of each data file and control file backup set
# (autobackups excluded)
CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 2;
# Makes 3 copies of every archived redo log backup to tape
CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE sbt TO 3;

To return a BACKUP COPIES configuration to its default value, run the same CONFIGURE command with the CLEAR option, as in the following example:

CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE sbt CLEAR;

By default, CONFIGURE ... BACKUP COPIES is set to 1 for each device type.

Sometimes you may want to omit a specified tablespace from part of the regular backup schedule. Here are some possible scenarios to consider:

• A tablespace is easy to rebuild, so it is more cost-effective to rebuild it than back it up every day.

• A tablespace contains temporary or test data that you do not need to back up.

• A tablespace does not change often and therefore should be backed up on a different schedule from other backups.

You can run CONFIGURE EXCLUDE FOR TABLESPACE to exclude the specified tablespace from the BACKUP DATABASE command. The exclusion condition applies to any data files that you add to this tablespace in the future.

For example, you can exclude testing tablespaces cwmlite and example from whole database backups as follows:

CONFIGURE EXCLUDE FOR TABLESPACE cwmlite;
CONFIGURE EXCLUDE FOR TABLESPACE example;

If you run the following command, then RMAN backs up all tablespaces in the database except cwmlite and example:

BACKUP DATABASE;

You can still back up the configured tablespaces by explicitly specifying them in a BACKUP command or by specifying the NOEXCLUDE option on a BACKUP DATABASE command. For example, you can enter one of the following commands:

BACKUP DATABASE NOEXCLUDE; #backs up database, including cwmlite and example
BACKUP TABLESPACE cwmlite, example;  # backs up only cwmlite and example

You can disable the exclusion feature for cwmlite and example as follows:

CONFIGURE EXCLUDE FOR TABLESPACE cwmlite CLEAR;
CONFIGURE EXCLUDE FOR TABLESPACE example CLEAR;

RMAN includes these tablespaces in future whole database backups.

You can see the current snapshot location by running the SHOW command. This example shows a snapshot location that is determined by the default rule:

RMAN> SHOW SNAPSHOT CONTROLFILE NAME;
CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/oracle/dbs/snapcf_trgt.f'; # default

This example shows a snapshot control file that has a nondefault file name:

RMAN> SHOW SNAPSHOT CONTROLFILE NAME;
CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/oracle/oradata/trgt/snap_trgt.ctl';

Use the CONFIGURE SNAPSHOT CONTROLFILE NAME TO 'filepath' command to change the name and path of the snapshot control file. Subsequent snapshot control files that RMAN creates use the specified name and path.

In an Oracle Real Application Clusters (Oracle RAC) environment, the snapshot control file location must be on shared storage—that is, storage that is accessible to all Oracle RAC instances.

For example, start RMAN, connect to the target database, and then enter:

CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/oracle/oradata/trgt/snap_trgt.ctl';

You can also set the snapshot control file name to a raw device.

To reset the snapshot control file location to the default, run the CONFIGURE SNAPSHOT CONTROLFILE NAME CLEAR command.