C100DBA Philosophy and Features Practice Question
A global e-commerce platform uses MongoDB with a replica set spanning three data centers. The company wants to ensure that a write is acknowledged by a majority of voting members before it is considered successful, even if one data center experiences a network partition. Which write concern should be configured to meet this requirement?
⚠ Common exam trap
The trap here is assuming that w: 2 always provides majority acknowledgment, but in a replica set with more than three members, 2 may not constitute a majority.
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
✓
w: majority
w: majority ensures that a write is acknowledged by a majority of voting members in the replica set, providing strong durability guarantees even in the event of a network partition affecting one data center. This write concern is essential for applications that cannot tolerate data loss and need to maintain consistency across geographically distributed nodes.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
w: 1
Why it's wrong here
w: 1 acknowledges the write once it has been applied to the primary node only. This does not guarantee that the write has been replicated to other data centers, so a network partition or primary failure could result in data loss if the primary goes down before replication. It does not meet the requirement of acknowledgment by a majority of voting members.
- ✗
w: 2
Why it's wrong here
w: 2 acknowledges the write once it has been applied to the primary and one secondary. While this provides redundancy, it does not guarantee that a majority of voting members have acknowledged the write. In a replica set with an even number of members or during elections, w: 2 might not be sufficient to prevent rollbacks. It is less robust than w: majority for multi-data-center scenarios.
- ✓
w: majority
Why this is correct
w: majority requires that a write be acknowledged by a majority of the voting members in the replica set. In a three-data-center deployment, this ensures that the write is persisted to multiple locations before being considered successful, providing durability even if one data center is partitioned. This aligns with the requirement for high reliability across data centers.
- ✗
w: 0
Why it's wrong here
w: 0 disables write acknowledgment entirely, meaning the client does not wait for any confirmation. This offers the lowest latency but no durability guarantees. It is unsuitable for an e-commerce platform that requires data to be safely replicated across data centers before considering a write successful.
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.