Using an arbiter allows one to easily ensure an odd number of voters in replica sets. Why is this important?

Question

Options

• ATo help in disaster recovery
• BTo protect agains network partitions
• CTo enable certain read preference settings
• DTo add greather redundancy
• EFor more efficient backup operations

• B
  93% (39)
• C
  2% (1)
• D
  5% (2)

Explanation

An odd number of voters in a replica set is critical for preventing split-brain scenarios during network partitions - when a partition divides nodes into groups, a majority quorum (more than half of all votes) is required to elect a primary, and odd numbers guarantee one side can always achieve majority while the other cannot, avoiding two simultaneous primaries.

Why the distractors are wrong:

• A (disaster recovery): Replica sets do aid recovery, but that benefit comes from having multiple data-bearing members, not from voter count parity.
• C (read preference settings): Read preferences (primary, secondary, nearest, etc.) are independent of voter count and work regardless of even or odd membership.
• D (redundancy): Arbiters hold no data, so they add zero redundancy - they only contribute a vote.
• E (backup efficiency): Backup operations are unrelated to voter count; backups typically target a secondary data node.

Memory tip: Think of it like a tied jury - if you have an even split (e.g., 2 vs. 2), no verdict can be reached and the cluster stalls. An odd number of voters breaks the tie and ensures someone wins the election.

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