What is the replication factor for a replicated cluster with 1 primary, 3 secondaries with one of them hidden. The set also has an arbiter?

Question

Options

• ANone of the above
• B5
• C3
• D4

• A
  6% (2)
• B
  3% (1)
• C
  13% (4)
• D
  78% (25)

Explanation

Option D (4) is correct because the replication factor counts only data-bearing members: 1 primary + 3 secondaries (including the hidden one) = 4 copies of data. A hidden secondary is invisible to client applications and cannot serve reads, but it still stores a full copy of the data, so it counts toward the replication factor.

Why the distractors fail:

• B (5) incorrectly counts the arbiter as a data-bearing node - arbiters participate in elections but store no data.
• C (3) likely excludes either the hidden secondary or the primary, both of which hold data.
• A (None of the above) is wrong because 4 is the correct answer.

Memory tip: Use the phrase "Hidden holds, Arbiter abstains" - hidden secondaries still hold data (count them), while arbiters only vote in elections (never count them for replication factor).

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