This DEA-C01 practice question tests your understanding of data store management. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 needs to store time-series sensor data from thousands of IoT devices. The data is written once, read frequently for the last 24 hours, and rarely accessed after 30 days. Which storage solution is MOST cost-effective?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Amazon Timestream with a 30-day retention policy.
Amazon Timestream is purpose-built for time-series data, offering automatic storage tiering where recent data resides in memory for fast queries and historical data is moved to a cost-optimized magnetic store. A 30-day retention policy aligns perfectly with the requirement to keep data accessible for frequent reads over the last 24 hours while automatically expiring older data, minimizing storage costs without manual intervention.
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.
✗
Amazon Redshift with automatic compression and distribution keys.
Why it's wrong here
Redshift is more expensive and not ideal for high-frequency writes of small records.
✗
Amazon DynamoDB with TTL to expire data after 30 days.
Why it's wrong here
DynamoDB is optimized for key-value access and can be costly for high write throughput of sensor data.
✓
Amazon Timestream with a 30-day retention policy.
Why this is correct
Timestream is designed for time-series data, with cost-effective tiered storage and built-in analytics.
Related concept
Read the scenario before looking for a memorised answer.
✗
Amazon S3 with lifecycle policies to transition to S3 Glacier after 30 days.
Why it's wrong here
S3 does not natively support time-series queries; additional services like Athena are needed, increasing cost and complexity.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose Amazon S3 with lifecycle policies (Option D) because they associate S3 with cost-effective storage, but they overlook the requirement for frequent reads of recent data, which S3 cannot serve with low latency without additional caching layers, and they miss that Timestream is the only AWS service natively designed for time-series data with automatic tiering and retention.
Detailed technical explanation
How to think about this question
Amazon Timestream uses a dual-storage architecture: a memory store for recent data (configurable retention, e.g., 24 hours) enabling sub-second query latency, and a magnetic store for historical data with lower cost and higher compression. Under the hood, Timestream automatically partitions data by time and dimensions, and its query engine uses a specialized time-series SQL dialect with functions like `BIN()` and `INTERPOLATE_LINEAR()` to handle irregular sensor data efficiently. In a real-world scenario, a fleet of 10,000 sensors emitting data every second would generate 864 million writes per day, which Timestream can ingest via the WriteRecords API with batching, while Redshift or DynamoDB would struggle with cost or write throughput limits.
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: Amazon Timestream with a 30-day retention policy. — Amazon Timestream is purpose-built for time-series data, offering automatic storage tiering where recent data resides in memory for fast queries and historical data is moved to a cost-optimized magnetic store. A 30-day retention policy aligns perfectly with the requirement to keep data accessible for frequent reads over the last 24 hours while automatically expiring older data, minimizing storage costs without manual intervention.
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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