How to made backup database RMAN tobe single file piece backup

Hello Oracle Master
I have question here

My database is spread in 3 storage and every storage store some datafile. here the storage

/dev/sdc             154818540  27852340 119101880  19% /Data01
/dev/sde             123854820  15822656 101740708  14% /Others01
/dev/sdf             154818540  11974300 134979920   9% /Index01

when perform RMAN backup, the result is many backup piece file created here the sample result
-rw-r----- 1 visdb orcl 8788541440 Mar  3 20:43 ACS_DB03032012_0qn4vfml_1_1.bkp
-rw-r----- 1 visdb orcl 4399030272 Mar  3 20:50 ACS_DB03032012_0rn4vfp0_1_1.bkp
-rw-r----- 1 visdb orcl 4239392768 Mar  3 20:57 ACS_DB03032012_0sn4vfqd_1_1.bkp
-rw-r----- 1 visdb orcl 2698559488 Mar  3 21:02 ACS_DB03032012_0tn4vfrq_1_1.bkp
-rw-r----- 1 visdb orcl 1836834816 Mar  3 21:05 ACS_DB03032012_0un4vfsu_1_1.bkp
-rw-r----- 1 visdb orcl  755515392 Mar  3 21:06 ACS_DB03032012_0vn4vftn_1_1.bkp