In a five-node distributed system, what is the minimum quorum needed to avoid split-brain and proceed with operations?

In a five-node distributed system, what is the minimum quorum needed to avoid split-brain and proceed with operations?

• A. 3
• B. 2
• C. 4
• D. 5

Answer: (A)

Quorum is the minimum number of nodes that must agree to move forward, ensuring decisions come from a single, consistent majority and preventing split-brain when the cluster splits. In a five-node system, a majority means more than half, so at least three nodes must concur. With a partition leaving three on one side and two on the other, only the three-node side reaches quorum and proceeds, while the two-node side cannot. If the threshold were higher, availability would suffer when nodes fail; if it were lower, split-brain could happen because both partitions might reach the threshold. So the smallest safe quorum for five nodes is a majority.

Quorum is the minimum number of nodes that must agree to move forward, ensuring decisions come from a single, consistent majority and preventing split-brain when the cluster splits. In a five-node system, a majority means more than half, so at least three nodes must concur. With a partition leaving three on one side and two on the other, only the three-node side reaches quorum and proceeds, while the two-node side cannot. If the threshold were higher, availability would suffer when nodes fail; if it were lower, split-brain could happen because both partitions might reach the threshold. So the smallest safe quorum for five nodes is a majority.