The number of voting files you can store in a particular Oracle ASM disk group depends upon the redundancy of the disk group. External redundancy: A disk group with external redundancy can store only one voting disk Normal redundancy: A disk group with normal redundancy stores three voting disks High redundancy: A disk group with high redundancy stores five voting disks
Normal redundancy In a normal redundancy disk group, to increase performance and reliability, Oracle ASM by default uses two-way mirroring. A normal redundancy disk group requires a minimum of two disk devices (or two failure groups). The effective disk space in a normal redundancy disk group is half the sum of the disk space in all of its devices. For Oracle Clusterware files, Normal redundancy disk groups provide 3 voting disk files, 1 OCR and 2 copies (one primary and one secondary mirror). With normal redundancy, the cluster can survive the loss of one failure group. For most installations, Oracle recommends that you select normal redundancy.