Exam NS0-520 topic 1 question 51 discussion

A&C...The quorum rule states that to make changes to the configuration in our cluster, we need to have more than half of the nodes available. This prevents configuration conflicts if we lose connectivity between the nodes in our cluster. So, if we have only 2 racks and 4 nodes we could never get more than half of the nodes available if one of those racks power fails. We need 6 nodes separated on 3 racks, so we can have more than half of the nodes available if one of those racks power fails.

Correct Answer is A and C To maintain quorum in the event of a rack-level power failure, you must ensure that a majority of the cluster nodes remain online and able to communicate. In ONTAP, quorum is achieved when more than half the nodes are operational and can communicate with each other. If you have only two racks and one fails, you could lose half the nodes, resulting in a loss of quorum (since you need a simple majority-more than half). By distributing nodes across three racks, even if an entire rack fails, two-thirds of the nodes remain, maintaining quorum.

B & D are correct. Because there is the possibility of a tie in a cluster that has an even number of nodes, one node has an extra fractional voting weight called epsilon. If the connectivity between two equal portions of a large cluster fails, the group of nodes containing epsilon maintains quorum, assuming that all of the nodes are healthy. For example, the following illustration shows a four-node cluster in which two of the nodes have failed. However, because one of the surviving nodes holds epsilon, the cluster remains in quorum even though there is not a simple majority of healthy nodes. https://docs.netapp.com/us-en/active-iq-unified-manager/health-checker/concept_understand_quorum_and_epsilon.html