Various parameters that specify limits can be set for a backup. To use the RMAN-specified limits, choose Use RMAN defaults for maximum limits.

To set custom limits, choose Specify maximum limits.

In the Maximum I/O Limits box, modify Read rate to change the maximum number of blocks per second that will be read from each input data file. Each block is of size DB_BLOCK_SIZE * DB_FILE_DIRECT_IO_COUNT. Use this parameter to ensure that the command does not consume excessive disk bandwidth and thereby degrade online performance.

Modify Size of a backup piece to change the maximum size of each backup piece.

Modify Number of open files to change the maximum number of input files that the backup will have open at any given time. Use this parameter to prevent "Too many open files" O/S error messages when backing up a large number of files into a single backup set.

In the Maximum Backup Set Limits box, modify Number of files per backup set to change the maximum number of files (backup pieces) to place in one backup set. If the number of files to backup is greater than this value, RMAN will create multiple backup sets.

Modify Size of the backup set to change the maximum size of the backup set. RMAN attempts to limit all backup sets to this size, which is useful when you want to make each backup set no larger than one tape.

Modify Size of the backup set for archived logs to change the maximum size of the backup set for a backup of archived redo logs. RMAN attempts to limit all backup sets to this size, which is useful when you want to make each backup set no larger than one tape.

In the I/O Output box, the Number of parallel streams setting controls the degree of parallelism within a backup. This number specifies the maximum number of connections between RMAN and a database instance. Each connection initiates an Oracle server session on the target instance: this server session performs the work of backing up backup sets.

For more information on backup limits refer to the Oracle Backup and Recovery Guide.