The answer is S3 Glacier Deep Archive. This is the most cost-effective choice for long-term archival data because it offers the lowest storage cost of any S3 storage class, specifically designed for data that is accessed less than once a year and retained for 7 years or more. For append-only sensor data older than 30 days, the 12-hour retrieval time is perfectly acceptable given the infrequent access pattern, and the compliance requirement for 7-year retention makes the minimal storage expense the primary optimization goal. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your ability to match access frequency and retention duration to the correct storage tier, with a common trap being to select S3 Glacier Instant Retrieval or S3 Glacier Flexible Retrieval due to faster access times, which are unnecessary and more costly here. Remember the memory tip: for data that is "cold, old, and rarely told," choose Deep Archive.
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 data engineer is designing a data lake on Amazon S3 for storing raw sensor data. The data is append-only and accessed infrequently after 30 days. Compliance requires that data be retained for 7 years. Which S3 storage class is the MOST cost-effective for data older than 30 days?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
S3 Glacier Deep Archive
B is correct because Amazon S3 Glacier Deep Archive is the most cost-effective storage class for data that is accessed infrequently and must be retained for long periods (7 years). For data older than 30 days, the retrieval time of 12 hours is acceptable given the append-only, infrequent access pattern, and the storage cost is significantly lower than other classes.
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.
✗
S3 Standard-IA
Why it's wrong here
Standard-IA is for infrequent access but has higher storage costs than Glacier Deep Archive.
✓
S3 Glacier Deep Archive
Why this is correct
This is the lowest-cost storage class for long-term archival data with infrequent access.
Related concept
Read the scenario before looking for a memorised answer.
✗
S3 One Zone-IA
Why it's wrong here
One Zone-IA does not provide the same durability (99.99%) and is not recommended for compliance data.
✗
S3 Intelligent-Tiering
Why it's wrong here
Intelligent-Tiering automatically moves data, but if data is never accessed, it will stay in frequent access tier and cost more.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose S3 Glacier Flexible Retrieval (not listed) or S3 Standard-IA, mistakenly thinking that faster retrieval is necessary for compliance data, when in fact the 12-hour retrieval time of Glacier Deep Archive is sufficient for infrequent access patterns and offers the lowest cost.
Detailed technical explanation
How to think about this question
S3 Glacier Deep Archive uses a redundant storage infrastructure across at least three Availability Zones, providing 99.999999999% durability. The retrieval time is 12 hours for standard retrievals, which is acceptable for compliance data that is rarely accessed. Under the hood, data is stored on tape-like media with erasure coding, and the retrieval process involves staging data to a temporary location before it becomes accessible via S3 API calls.
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: S3 Glacier Deep Archive — B is correct because Amazon S3 Glacier Deep Archive is the most cost-effective storage class for data that is accessed infrequently and must be retained for long periods (7 years). For data older than 30 days, the retrieval time of 12 hours is acceptable given the append-only, infrequent access pattern, and the storage cost is significantly lower than other classes.
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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