The answer is to configure the EMR cluster to use instance store volumes for intermediate data instead of EMRFS. This is correct because Spark shuffle operations generate massive amounts of intermediate data that, when written to Amazon S3 via EMRFS, cause high network I/O and incur significant S3 storage costs. Instance store volumes, which are physically attached to the cluster nodes, provide local, ephemeral storage with much lower latency and no network transfer costs, making them ideal for temporary shuffle data. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of EMR storage optimization and the trade-offs between EMRFS and local storage for transient workloads. A common trap is assuming that increasing node count or EBS volumes will solve the I/O bottleneck, but these either increase cost or fail to address the root cause of network-bound shuffle traffic. Memory tip: think of instance store as a scratch pad—fast, local, and temporary—perfect for shuffle data that doesn’t need to persist.
DEA-C01 Data Store Management Practice Question
This DEA-C01 practice question tests your understanding of data store management. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 of 20 nodes. The cluster stores intermediate data on Amazon S3 using EMRFS. The company's data engineering team notices that the Spark jobs are running slower than expected. Upon investigating, they find that the cluster is experiencing high network I/O and that the S3 storage costs have increased significantly. The team suspects that the Spark jobs are writing too much intermediate data to S3. The jobs are performing many shuffle operations. The team wants to optimize the job performance and reduce costs without modifying the Spark application code. What should the data engineer do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure the EMR cluster to use instance store volumes for intermediate data instead of EMRFS.
Option C is correct because enabling automatic encryption on the bucket does not affect performance; the issue is about shuffle data. Option B is wrong because increasing EBS volumes for shuffle storage on instance nodes is not standard; EMR uses instance store or EMRFS. Option A is correct because using instance store for shuffle data reduces S3 I/O and cost. Option D is wrong because increasing node count may increase cost and network 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.
✗
Enable S3 server-side encryption on the S3 bucket to reduce storage costs.
Why it's wrong here
Encryption does not reduce storage costs.
✗
Increase the size of the EBS root volumes on the cluster nodes to store more intermediate data locally.
Why it's wrong here
EBS volumes are not used for shuffle by default; increasing them won't help.
✓
Configure the EMR cluster to use instance store volumes for intermediate data instead of EMRFS.
Why this is correct
Instance store provides local ephemeral storage, reducing S3 dependency and network I/O.
Related concept
Read the scenario before looking for a memorised answer.
✗
Add more nodes to the cluster to distribute the shuffle load.
Why it's wrong here
More nodes may increase network I/O and cost.
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 DEA-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 Store Management — This question tests Data Store Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure the EMR cluster to use instance store volumes for intermediate data instead of EMRFS. — Option C is correct because enabling automatic encryption on the bucket does not affect performance; the issue is about shuffle data. Option B is wrong because increasing EBS volumes for shuffle storage on instance nodes is not standard; EMR uses instance store or EMRFS. Option A is correct because using instance store for shuffle data reduces S3 I/O and cost. Option D is wrong because increasing node count may increase cost and network I/O.
What should I do if I get this DEA-C01 question wrong?
Identify which DEA-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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Question Discussion
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