6 Configuring the RMAN Environment: Advanced Topics

About Channel Control Options

Whether you allocate channels manually or use automatic channel allocation, you can use channel commands and options to control behavior. Table 6-1 summarizes the ways in which you can control channel behavior. Unless noted, all channel parameters are supported in both CONFIGURE CHANNEL and ALLOCATE CHANNEL commands.

Configuring Specific Channel Parameters

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 will be 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 could be 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.

CONFIGURE DEFAULT DEVICE TYPE TO disk;        # backup goes to disk
CONFIGURE DEVICE TYPE sbt PARALLELISM 2;      # two channels used in in parallel
CONFIGURE CHANNEL 1 DEVICE TYPE DISK FORMAT '/disk1/%U' # 1st channel to disk1 
CONFIGURE CHANNEL 2 DEVICE TYPE DISK FORMAT '/disk2/%U' # 2nd channel to disk2
BACKUP DATABASE; # backup - first channel goes to disk1 and second to disk2

CONFIGURE DEFAULT DEVICE TYPE TO sbt;    # backup goes to sbt
CONFIGURE DEVICE TYPE sbt PARALLELISM 2; # two sbt channels allocated by default
# Configure channel 1 to pool named first_pool
CONFIGURE CHANNEL 1 DEVICE TYPE sbt 
  PARMS 'ENV=(OB_MEDIA_FAMILY=first_pool)'; 
# configure channel 2 to pool named second_pool
CONFIGURE CHANNEL 2 DEVICE TYPE sbt 
  PARMS 'ENV=(OB_MEDIA_FAMILY=second_pool)'; 
BACKUP DATABASE; # first stream goes to 'first_pool' and second to 'second_pool'

ORA_SBT_TAPE_1
ORA_SBT_TAPE_2
ORA_SBT_TAPE_3

Configuring the Maximum Size of Backup Sets

In tape backups, it is possible for a multiplexed backup set to span multiple tapes, which means that blocks from each datafile 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 datafile rather than a partial datafile. You can use MAXSETSIZE to specify that each backup set should fit 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 will be 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 used in the BACKUP command.

Configuring the Maximum Size of Backup Pieces

Backup piece size is an issue in situations where 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 always limit the backup piece size to 2 GB 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;

Configuring Backup Duplexing

You can use the CONFIGURE ... BACKUP COPIES command to specify how many copies of each backup piece should be 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 datafiles, 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 datafile 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.

Configuring Tablespaces for Exclusion from Whole Database Backups

In some cases you may want to exclude specified tablespace part of the regular backup schedule, as in these cases:

• 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 datafiles 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:

# backs up the whole database, including cwmlite and example
BACKUP DATABASE NOEXCLUDE;
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.

Configuring the Backup Compression Algorithm

You can choose which compression algorithm that RMAN uses for backups. By default, RMAN uses ZLIB compression, which is very fast but has a compression ratio that is not as good as the ratio of other algorithms. BZIP2 has a very good compression ratio, but is slower than ZLIB. In short, the ZLIB algorithm is faster than BZIP2, but this improvement in speed is obtained at the cost of a slightly worse compression ratio.

The default compression algorithm is BZIP2. Note that the COMPATIBLE initialization parameter must be set to 11.0.0 or higher for ZLIB compression.

You can configure the compression algorithm with the following syntax, where alg_name is a placeholder specifying either BZIP2 or ZLIB.

CONFIGURE COMPRESSION ALGORITHM TO 'alg_name';

Configuring Backup Encryption

For improved security, you can configure backup encryption for RMAN backup sets. Encrypted backups cannot be read if they are obtained by unauthorized users. This feature requires the Enterprise Edition of the database.

SET ENCRYPTION ON;

CONFIGURE ENCRYPTION FOR DATABASE OFF;

Viewing the Configured Location of the Snapshot Control File

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 filename:

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

Setting the Location of the Snapshot Control File

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

For example, start RMAN 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 LOCATION CLEAR command.