Why ODD number of Voting Disks is recomended

An odd number of voting disks is required for proper clusterware configuration. A node must be able to strictly access more than half of the voting disks at any time. So, in order to tolerate a failure of n voting disks, there must be at least 2n+1 configured. (n=1 means 3 voting disks). You can configure up to 31 voting disks, providing protection against 15 simultaneous disk failures.

If you lose 1/2 or more of all of your voting disks, then nodes get evicted from the cluster, or nodes kick themselves out of the cluster. It doesn't threaten database corruption. Alternatively you can use external redundancy which means you are providing redundancy at the storage level using RAID.

For this reason when using Oracle for the redundancy of your voting disks, Oracle recommends that customers use 3 or more voting disks.

Note.For Oracle 11.2 you must have at least 300M size of OCR and Voting disks.