There are a number of features you can use to tune your backup performance, once you have sufficient knowledge of your database and its workload and bottlenecks.
Using the RATE Parameter to Control Disk Bandwidth Usage
The RATE parameter specifies the bytes/second that RMAN reads on this channel. Use this parameter to set an upper limit for bytes read so that RMAN does not consume excessive disk bandwidth and degrade online performance.
For example, set RATE=1500K. If each disk drive delivers 3 MB/second, then RMAN leaves some disk bandwidth available to the online system.
