The answer is using the EMR File System (EMRFS) to store data in Amazon S3, which directly enables Amazon EMR storage cost reduction compared to on-premises HDFS. This works because EMRFS allows you to decouple compute from storage, eliminating the need for HDFS’s default three-way replication overhead; instead, S3’s built-in durability and lower per-GB cost mean you pay only for what you store, not for redundant copies. On the AWS Certified Data Engineer Associate DEA-C01 exam, this concept tests your understanding of cost-optimized data lake architectures, often appearing in scenario-based questions where a company migrates from HDFS to EMR. A common trap is assuming you must keep HDFS on EMR for performance, but the exam emphasizes that S3 Standard-IA can further reduce costs for infrequently accessed data. Memory tip: think “EMRFS = S3 = no triple copy” to recall that storage savings come from avoiding HDFS replication.
DEA-C01 Data Store Management Practice Question
This DEA-C01 practice question tests your understanding of data store management. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 is migrating an on-premises Apache Hadoop cluster to Amazon EMR. The cluster uses HDFS for storage. Which THREE features of Amazon EMR help reduce storage costs compared to on-premises HDFS? (Choose THREE)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Leverage Amazon S3 storage classes like S3 Standard-IA for older data.
Option A is correct because Amazon S3 Standard-IA (Infrequent Access) offers lower storage costs than S3 Standard for data that is accessed less frequently, making it ideal for older or archival data in a Hadoop migration. By using S3 as the primary storage layer via EMRFS, you decouple compute from storage and avoid the replication overhead of HDFS (which typically uses 3x replication), significantly reducing storage costs.
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.
✓
Leverage Amazon S3 storage classes like S3 Standard-IA for older data.
Why this is correct
S3 storage classes allow cost optimization for infrequently accessed data.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use instance store volumes for intermediate data.
Why it's wrong here
Instance store volumes are ephemeral and do not provide cost savings for persistent storage.
✓
Enable automatic data compression in EMRFS.
Why this is correct
Compression reduces storage costs by reducing data size in S3.
Related concept
Read the scenario before looking for a memorised answer.
✓
Use EMR File System (EMRFS) to store data in Amazon S3.
Why this is correct
S3 is cheaper than HDFS and provides durability and scalability.
Related concept
Read the scenario before looking for a memorised answer.
✗
Attach Amazon EBS volumes to cluster nodes for persistent storage.
Why it's wrong here
EBS volumes add cost and are not a cost-saving feature.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse instance store volumes or EBS volumes as cost-saving alternatives, but the exam tests the understanding that S3-based storage with EMRFS is the primary mechanism for reducing storage costs in EMR by eliminating HDFS replication and enabling lifecycle management.
Detailed technical explanation
How to think about this question
EMRFS allows you to use Amazon S3 as a drop-in replacement for HDFS, leveraging S3's 99.999999999% durability and lifecycle policies to automatically transition older data to lower-cost storage classes like S3 Standard-IA or S3 Glacier. Under the hood, EMRFS uses a consistent view layer to handle S3's eventual consistency, and it supports server-side encryption and data compression (e.g., with gzip or snappy) to further reduce storage footprint and costs.
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.
TExam Day Tips
→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 exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: Leverage Amazon S3 storage classes like S3 Standard-IA for older data. — Option A is correct because Amazon S3 Standard-IA (Infrequent Access) offers lower storage costs than S3 Standard for data that is accessed less frequently, making it ideal for older or archival data in a Hadoop migration. By using S3 as the primary storage layer via EMRFS, you decouple compute from storage and avoid the replication overhead of HDFS (which typically uses 3x replication), significantly reducing storage costs.
What should I do if I get this DEA-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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