If a cluster is in quorum, what is the minimum number of participating nodes that must be healthy?

Two-thirds is a stricter threshold than the quorum requirement - clustered ONTAP only needs a simple majority, not two-thirds of nodes.

Quorum in clustered Data ONTAP requires a simple majority of nodes to be healthy and participating, meaning strictly more than 50% of the total node count must be operational. This threshold ensures that in any network partition, only one segment can hold a majority and therefore only one segment can continue serving data. If fewer than a simple majority of nodes are reachable, the cluster halts data services to prevent data corruption from conflicting writes.

Three-quarters is an overly restrictive threshold; quorum is established with just a simple majority, not three-quarters of participating nodes.

Exactly half (50%) is insufficient for quorum because a tie condition cannot resolve which partition should continue operating - a simple majority means more than half.