You have a replicated cluster with 1 primary, 3 secondary, 1 arbiter. One of the secondary is hidden. What is the replication factor of this replicated cluster?

Question

Options

• A7
• B03
• C04
• D06

• A
  4% (1)
• B
  4% (1)
• C
  80% (20)
• D
  12% (3)

Explanation

Replication factor counts how many nodes store actual data copies. Option C (4) is correct because: 1 primary + 3 secondaries (including the hidden secondary) = 4 data-bearing nodes. The hidden secondary still holds a full data copy - "hidden" only means it's invisible to client reads and ineligible for primary election, not that it skips replication.

Why the distractors are wrong:

• B (3): A common trap - counting only the visible secondaries and forgetting the primary, or excluding the hidden secondary under the mistaken belief it doesn't replicate.
• D (6): Likely results from counting all 5 replica set members and adding something extra, or confusing total members with data copies.
• A (7): No standard calculation produces 7 from this topology; this is a distractor with no meaningful basis.

Memory tip: The formula is replication factor = total members − arbiters. Arbiters vote but never store data, so subtract them. Hidden nodes still replicate, so count them normally. Here: 5 total − 1 arbiter = 4.

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