The answer is to replace the core nodes with r5d.xlarge instances that have local SSDs. This improves EMR Spark I/O performance because local NVMe SSDs provide high-speed, low-latency storage for caching intermediate shuffle data, which reduces the need to read repeatedly from S3 over the network, thereby lowering network throughput while allowing CPU utilization to rise. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this scenario tests your understanding of instance families and storage optimization for I/O intensive Spark jobs—a common trap is assuming more nodes or cheaper instances will fix performance, but the key is matching the workload to the right hardware. Remember the mnemonic: for I/O pain, add an SSD to the node, not more nodes to the cluster.
MLS-C01 Data Engineering Practice Question
This MLS-C01 practice question tests your understanding of data engineering. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company uses Amazon EMR to run Spark jobs on a cluster with 10 core nodes of type r5.xlarge. The jobs are I/O intensive and read large amounts of data from S3. The team notices high network throughput but low CPU utilization. Which configuration change would improve job performance at the same cost?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Replace the core nodes with r5d.xlarge instances that have local SSDs.
Option B is correct because r5d instances include local NVMe SSDs, which can be used for caching intermediate data, reducing network I/O and improving performance for I/O intensive jobs. Option A is wrong because increasing core nodes increases cost. Option C is wrong because using spot instances reduces cost but not performance. Option D is wrong because moving to m5 instances (general purpose) may not improve I/O.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Change the instance type to m5.xlarge (general purpose) to balance resources.
Why it's wrong here
m5 instances have lower network and EBS performance than r5.
✗
Increase the number of core nodes to 20.
Why it's wrong here
This doubles the cost.
✓
Replace the core nodes with r5d.xlarge instances that have local SSDs.
Why this is correct
Local SSDs provide high I/O for caching, reducing network traffic.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use spot instances for the core nodes to save cost and reinvest in more nodes.
Why it's wrong here
Spot instances reduce cost but do not improve performance directly.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Identify which MLS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Data Engineering — This question tests Data Engineering — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Replace the core nodes with r5d.xlarge instances that have local SSDs. — Option B is correct because r5d instances include local NVMe SSDs, which can be used for caching intermediate data, reducing network I/O and improving performance for I/O intensive jobs. Option A is wrong because increasing core nodes increases cost. Option C is wrong because using spot instances reduces cost but not performance. Option D is wrong because moving to m5 instances (general purpose) may not improve I/O.
What should I do if I get this MLS-C01 question wrong?
Identify which MLS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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This MLS-C01 practice question is part of Courseiva's free Amazon Web Services 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 MLS-C01 exam.
Question Discussion
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