The figure shows two OVS/dom0's.
The first OVS/dom0 contains 2 user domains: domU1 and domU3.
The second OVS/dom0 contains 2 user domains: domU2 and domU4.
domU1 contains /dev/exadata_quorum/QD_DATAC1_domU1 and /dev/exadata_quorum/QD_DATAC1_domU2.
domU3 contains /dev/exadata_quorum/QD_DATAC1_domU3 and /dev/exadata_quorum/QD_DATAC1_domU4.
domU2 contains /dev/exadata_quorum/QD_DATAC1_domU1 and /dev/exadata_quorum/QD_DATAC1_domU2.
domU4 contains /dev/exadata_quorum/QD_DATAC1_domU3 and /dev/exadata_quorum/QD_DATAC1_domU4.
RAC Cluster 1 connects to domU1 and domU2.
RAC Cluster 2 connects to domU3 and domU4.