PARALLELISM rman

You can achieve paralellism within yours script explicitly

run
{
allocate channel c1 type disk;
allocate channel c2 type disk;
backup
(datafile 1,2,3 channel c1)
(archivelog all channel c2);
}

Or

configure device type disk parallelism 3;

The backup command will be divided among the number of channels which you defined in the parallelsim config.

backup
(datafile 1,2)
(datafile 3,4)
(archivelog all)