0 INS-30510 Insufficient number of ASM Disks selected

While installing the Oracle, I have encounter the error : INS-30510 Insufficient number of ASM Disks selected

The normal redundancy requires 2 or more disks. If we install the RAC as standalone, we only needs two disks. Since I am installing the RAC cluster, we need at least three disks to store the voting and OCR disks.