In terms of performance, it's going to be very important that RMAN doesn't consume a lot of I/O bandwidth. It's also required that with the backup going on, the impact on the overall performance of the database shouldn't get impacted much. To control this, the following options are useful:
RATEparameterMAXPIECEparameterDURATIONparameter
Configuring the RATE parameter sets an upper level over the I/O that RMAN can do. This would be configured for a channel since the I/O would be done by the channel only. This parameter controls how much data can be read by one channel in terms of bytes, kilobytes, megabytes, or gigabytes. Using this parameter will restrict RMAN from doing a lot of I/O which causes an adverse impact on the underlying database's performance by exhausting the complete or maximum bandwidth of the disks. There is no defined optimal setting for this parameter, but you should set it to such a value that the disks will have some bandwidth...