C100DBA Replication Practice Question
Exhibit
rs.status()
{
"set": "mySet",
"members": [
{ "_id": 0, "stateStr": "PRIMARY", "optime": { "ts": Timestamp(1600000000, 1) } },
{ "_id": 1, "stateStr": "SECONDARY", "optime": { "ts": Timestamp(1600000000, 1) } },
{ "_id": 2, "stateStr": "ARBITER" }
]
}Refer to the exhibit. What is the primary function of the node with _id 2 in this replica set?
⚠ Common exam trap
Candidates often confuse arbiters with secondary nodes, incorrectly assuming that an arbiter replicates data or can be promoted to a primary node during a failover event, which is fundamentally false.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
It provides a vote during elections to help maintain a majority.
An arbiter exists solely to participate in elections and break ties. It does not replicate data or serve read requests, making it a low-resource way to achieve a majority vote in a set. This is crucial for environments where a full-data secondary is cost-prohibitive but high availability is still required to maintain quorum during network partitions.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It stores a copy of the data and can serve read queries.
Why it's wrong here
Arbiters do not contain data files or the capacity to sync data from the primary. They are intentionally designed to be lightweight, meaning they cannot participate in read scaling or serve as a redundant data source. Their sole purpose is to contribute a vote to the replica set consensus.
- ✗
It performs automatic failover by hosting a redundant copy of the oplog.
Why it's wrong here
Arbiters do not maintain an oplog, nor do they process any data replication. They are strictly limited to the voting process. If the primary fails, the arbiter helps elect a new primary, but it does not participate in the actual data recovery or the synchronization of the new primary.
- ✓
It provides a vote during elections to help maintain a majority.
Why this is correct
The arbiter is specifically configured to provide a voting member to the replica set without requiring the storage overhead of a data-bearing node. By participating in elections, it helps reach a majority of votes, which is required to elect a new primary during failover events in small sets.
- ✗
It acts as a load balancer for incoming read requests.
Why it's wrong here
Arbiters are not part of the read-routing path. Incoming read requests are handled by the primary or secondaries depending on the read preference. Since an arbiter does not hold data, it cannot answer queries, nor does it have any networking components configured to proxy or balance traffic for clients.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official MongoDB exam blueprint
This C100DBA practice question is part of Courseiva's free MongoDB certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the C100DBA exam.