C100DBA Server Administration Practice Question
Which TWO of the following are valid reasons to use an arbiter in a MongoDB replica set?
⚠ Common exam trap
Candidates incorrectly assume arbiters store a backup copy of the data or improve read performance, misunderstanding their sole purpose of breaking election ties.
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
✓
To break a tie in elections for replica sets with an even number of nodes.
Arbiters are lightweight processes that participate in elections but do not hold data. They are a cost-effective way to achieve a majority for elections in small replica sets. Understanding when to use an arbiter is crucial for designing a cost-efficient and highly available architecture, especially when deploying in multiple zones where adding a full data-bearing node might be cost-prohibitive or unnecessary due to data redundancy requirements.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
To increase the read throughput of the replica set.
Why it's wrong here
Arbiters do not hold data and therefore cannot serve read requests. Adding an arbiter will not improve read performance; instead, it only helps in maintaining the majority required for elections to ensure that the replica set can continue to function as a primary during network partitions or node failures.
- ✓
To break a tie in elections for replica sets with an even number of nodes.
Why this is correct
In an even-numbered replica set, an arbiter provides the necessary third vote to reach a majority during an election. This prevents the cluster from being unable to elect a primary, ensuring that the system remains highly available even if one of the two data-bearing nodes goes offline unexpectedly.
- ✗
To maintain a copy of the data for disaster recovery.
Why it's wrong here
Arbiters do not store data. Using an arbiter for disaster recovery is impossible because it does not maintain a database instance that can be restored. If all data-bearing nodes fail, the arbiter cannot be used to recover the data, making it unsuitable for backup or data redundancy purposes.
- ✓
To achieve a majority of votes with minimum hardware costs.
Why this is correct
Arbiters have minimal CPU and RAM requirements compared to data-bearing nodes. They provide a cost-effective solution to ensure quorum in a replica set without the expense of provisioning additional high-performance hardware, which is ideal for smaller deployments that need high availability but want to keep infrastructure costs down.
- ✗
To act as a hidden node for analytical queries.
Why it's wrong here
Arbiters are not hidden nodes and do not hold data, so they cannot run analytical queries. A 'hidden' node is a data-bearing node configured with 'hidden: true', which is a completely different architectural feature designed for specific read-heavy workloads or offline backups, not for participating in elections like an arbiter.
About these practice questions
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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.