The answer is Azure Blob Storage Cool tier, as it provides the most cost-effective storage for billions of small JSON files with infrequent access while meeting the requirement of retrieval within seconds. This tier is designed for data accessed less than once per month, offering lower storage costs than the Hot tier, yet it still delivers sub-second latency via HTTPS REST API, making it ideal for infrequently accessed but quickly needed blobs. On the AZ-305 exam, this scenario tests your understanding of access pattern-based tier selection, often appearing as a trap where candidates mistakenly choose the Archive tier for cost savings, forgetting that Archive has retrieval delays of hours, not seconds. Remember the memory tip: “Cool for occasional calls, Archive for archival halls”—if you need data in seconds, stay out of the deep freeze.
AZ-305 Design data storage solutions Practice Question
This AZ-305 practice question tests your understanding of design data storage solutions. 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.
You need to store billions of small JSON files (average 50 KB) that are accessed infrequently but must be available within seconds when requested. Which Azure 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
✓
Azure Blob Storage Cool tier
Azure Blob Storage Cool tier is the most cost-effective solution for storing billions of small JSON files (average 50 KB) that are infrequently accessed but require low-latency retrieval within seconds. The Cool tier offers low storage costs for data accessed less than once per month, while still providing sub-second access latency for individual blobs via HTTPSREST API, matching the 'available within seconds' requirement without the higher costs of Hot or premium tiers.
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.
✗
Azure SQL Database with a table storing JSON
Why it's wrong here
SQL Database is not optimized for file storage and would be expensive.
✗
Azure Files with SMB shares
Why it's wrong here
Azure Files is not designed for high-scale storage of small files.
✓
Azure Blob Storage Cool tier
Why this is correct
Cool tier offers low storage costs and low-latency access for infrequently accessed data.
Related concept
Read the scenario before looking for a memorised answer.
✗
Azure Cosmos DB with a container for each file
Why it's wrong here
Cosmos DB is not cost-effective for billions of small files.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose Azure Cosmos DB (Option D) because of its low-latency guarantees, but they overlook the massive cost difference for storing billions of small files, where Blob Storage's object storage model is far more economical for infrequently accessed data.
Detailed technical explanation
How to think about this question
Azure Blob Storage Cool tier uses a single storage account to hold billions of blobs in flat or hierarchical namespaces, with each blob accessible via a unique URL and REST API; the Cool tier's lower storage cost (approximately $0.01/GB/month vs. $0.018/GB for Hot) is achieved by accepting a higher per-access cost and a 30-day minimum storage duration, which is ideal for infrequently accessed data. Under the hood, Blob Storage stores each blob as an object with metadata, and retrieval latency remains consistently under a few seconds even for cold data because the data is still on SSD-backed storage, not archived to tape like the Archive tier. A real-world scenario is storing IoT device telemetry logs (each a small JSON file) that are rarely queried for compliance audits but must be instantly available when needed, where Cool tier balances cost and access speed.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this AZ-305 question in full detail.
Design data storage solutions — This question tests Design data storage solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Azure Blob Storage Cool tier — Azure Blob Storage Cool tier is the most cost-effective solution for storing billions of small JSON files (average 50 KB) that are infrequently accessed but require low-latency retrieval within seconds. The Cool tier offers low storage costs for data accessed less than once per month, while still providing sub-second access latency for individual blobs via HTTPS REST API, matching the 'available within seconds' requirement without the higher costs of Hot or premium tiers.
What should I do if I get this AZ-305 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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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Variation 1. A company needs to store millions of small JSON files (average 10 KB each) for a serverless application. The data must be accessed via HTTPS and support high read throughput. Which Azure storage solution is most cost-effective?
easy
✓ A.Azure Blob Storage (general-purpose v2, hot tier)
B.Azure Files (standard)
C.Azure Cosmos DB
D.Azure Table Storage
Why A: Azure Blob Storage (general-purpose v2, hot tier) is the most cost-effective solution because it provides native HTTPS access, high throughput for read-heavy workloads, and low-cost storage for small objects like JSON files. The hot tier optimizes for frequent access, and GPv2 accounts support the high request rates needed for millions of small files without premium pricing.
Last reviewed: Jun 24, 2026
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