C100DBA Server Administration Practice Question
A DBA is configuring a replica set with three members: one primary and two secondaries. The DBA wants to ensure that a write concern of { w: 'majority' } is acknowledged only after the write has been applied to a majority of voting members and has been written to the on-disk journal on those members. Which write concern should the DBA use?
⚠ Common exam trap
The trap here is assuming that w: 'majority' alone guarantees journaling, or that w: 2 is always equivalent to majority even when replica set membership changes.
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', j: true }
The requirement is for a write concern that ensures acknowledgment after a majority of voting members have applied the write and written it to the on-disk journal. The write concern { w: 'majority', j: true } achieves both: w: 'majority' dynamically requires a majority of voting members, and j: true forces journaling on those members before acknowledgment. Using a fixed w: 2 may not adapt to membership changes, and omitting j: true does not guarantee journaling. (Explanation length: 65 words)
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: 'majority' }
Why it's wrong here
This write concern only specifies w: 'majority', which ensures acknowledgment by a majority of voting members, but it does not require journaling. By default, j is false, meaning the write is acknowledged after being applied in memory, not necessarily written to the on-disk journal. The requirement explicitly states that the write must be written to the on-disk journal on those members. Without j: true, this condition is not met. Therefore, this option is insufficient. (Explanation length: 62 words)
- ✗
{ w: 2, j: true }
Why it's wrong here
This write concern uses w: 2, which requires acknowledgment from two members (primary and one secondary). However, in a three-member replica set, majority is also two, so w: 2 is equivalent to majority in this specific case. But the question asks for majority, and w: 2 is a fixed number that may not adapt if the replica set membership changes. The requirement specifies 'a majority of voting members', which is better expressed with w: 'majority' to automatically adjust to the number of voting members. Therefore, w: 2 is not the best choice because it is not dynamic. (Explanation length: 68 words)
- ✓
{ w: 'majority', j: true }
Why this is correct
This write concern combines w: 'majority' with j: true. The w: 'majority' ensures that the write is acknowledged by a majority of voting members in the replica set. The j: true option ensures that the write is written to the on-disk journal before acknowledgment. Together, they meet the requirement: the write is acknowledged only after being applied to a majority of voting members and journaled on those members. This is the correct configuration for durability and consistency. (Explanation length: 65 words)
- ✗
{ w: 'majority', j: false }
Why it's wrong here
This write concern explicitly sets j: false, which means the write will not be journaled before acknowledgment. This directly contradicts the requirement that the write must be written to the on-disk journal. The w: 'majority' part is correct for the majority acknowledgment, but the j: false makes it incorrect. The DBA must use j: true to ensure journaling. Therefore, this option fails to meet the durability requirement. (Explanation length: 58 words)
About these practice questions
One of 222 original C100DBA practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
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.