Configuring the Maximum Size of Backup Sets and Pieces

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.

You can set MAXSETSIZE in bytes (default), kilobytes (K), megabytes (M), and gigabytes (G). The default value is given in bytes and is rounded down to the lowest kilobyte value. For example, if you set the maximum set size to 2000, then RMAN rounds down this value to 1 kilobyte (1024 bytes). If you set the maximum set size to 2049, then RMAN rounds down this value to 2 kilobytes (2048 bytes).

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=(NSR_DATA_VOLUME_POOL=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.

Note:

There is no equivalent to MAXSETSIZE for controlling the size of image copies. Since an image copy is an exact duplicate of the file being backed up, its size must be identical to the source file.

This fact can present a problem with some older operating systems which limit the size of individual files. If you are using a raw partition to store a 10GB datafile, and your operating system only supports 4GB files on the file system, you cannot take image copy backups of that file.

Showing the Default Maximum Size of Backup Sets: SHOW MAXSETSIZE

You can use SHOW MAXSETSIZE to view the maximum backup set size set using CONFIGURE MAXSETSIZE. The size of a backup set is measured in the total bytes of the included backup pieces. After connecting to the target database and recovery catalog (if you use one), issue the SHOW MAXSETSIZE command. For example, enter:

SHOW MAXSETSIZE;      # shows the CONFIGURE MAXSETSIZE settings

Sample output for SHOW MAXSETSIZE follows:

RMAN configuration parameters are:
CONFIGURE MAXSETSIZE TO 3072K;