Voting Disks is like an “Database Instance” and OCR is like a “Database”. During startup of Cluster Oracle first read and open all Voting Disks and after ASM be Started Oracle read and open all OCR.
So, Oracle does not need of ASM Instance be started or DISKGROUP be mounted to read and open Voting Disk.
Voting Disk also known as Voting files: Is a file that manages information about node membership.
How they are stored in ASM?
Voting disks are placed directly on ASMDISK.
Oracle Clusterware will store the votedisk on the disk within a disk group that holds the Voting Files. Oracle Clusterware does not rely on ASM to access the Voting Files, that’s means wich Oracle Clusterware does not need of Diskgroup to read and write on ASMDISK.
You cannot find/list Voting files using SQLPLUS(v$asm_diskgroup,v$asm_files,v$asm_alias), ASCMD utility or ASMCA gui.
You only know if exist a voting files in a ASMDISK (v$asm_disk using column VOTING_FILE). So, voting files not depend of Diskgroup to be accessed, does not mean that, we don’t need the diskgroup, diskgroup and voting file are linked by their settings.
Oracle Clusterware take configuration of DISKGROUP to configure the own voting files.
As Voting Disk are placed directly in ASMDISK of Diskgroup, we cannot use more than 1(one) Diskgroup.
The redundancy of voting files depend on ASMDISK not of Diskgroup.
When votedisk is on ASM diskgroup, no crsctl add option available. The number of votedisk is determined by the diskgroup redundancy.
If more copy of votedisk is desired, one can move votedisk to a diskgroup with higher redundancy
When votedisk is on ASM, no delete option available, one can only replace the existing votedisk group with another ASM diskgroup.
You cannot place Voting files in differents Diskgroup.
To use a quorum failgroup is required if you are using RAC Extended or if you are using more than 1 Storage in your cluster.
The COMPATIBLE.ASM disk group compatibility attribute must be set to 11.2 or greater to store OCR or voting disk data in a disk group.
Oracle Cluster Registry (OCR) and ASM Server Parameter File (ASM SPFILE):
OCR: The Oracle RAC configuration information repository that manages information about the cluster node list and
instance-to-node mapping information. OCR also manages information about Oracle Clusterware resource profiles
for customized applications.
The OCR is totally different from Voting Disk. Oracle Clusterware rely on ASM to access the OCR and SPFILE.
The OCR and SPFILE are stored similar to how Oracle Database files are stored.
The extents are spread across all the disks in the diskgroup and the redundancy (which is at the extent level)
is based on the redundancy of the disk group. For this reason you can only have one OCR in a diskgroup.
So, if your Diskgroup where OCR is stored become unavaliable you will lose your OCR and SPFILE.
Then we need put OCR mirror in another disk group to support failure of disk group.