Quick Answer
Azure Cosmos DB is the correct choice because it delivers native global distribution with multi-region writes and single-digit-millisecond latency at the 99th percentile, directly meeting the mobile app’s need for low-latency reads and writes worldwide. Its document model natively supports JSON documents with varying schemas, eliminating the need for schema management or complex migrations. On the AZ-305 exam, this scenario tests your ability to match workload characteristics—global low-latency NoSQL storage for mobile apps—to the appropriate service, often appearing as a distractor against Azure SQL Database or Azure Table Storage. A common trap is choosing Azure SQL Database for its JSON support, but it lacks native multi-region writes and sub-10ms latency guarantees. Remember: if the question says “global low-latency” and “JSON with varying schemas,” think Cosmos DB. Memory tip: “Cosmos connects continents in milliseconds—no schema, no limits.”
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 design a data storage solution for a mobile app that requires low-latency reads and writes globally. The data is JSON documents with varying schemas. Which Azure service should you choose?
Azure Cache for Redis
Why wrong: Redis is a cache, not a durable primary data store.
Azure Cosmos DB
Cosmos DB is a globally distributed NoSQL database with native JSON support and low-latency.
Azure SQL Database
Why wrong: Azure SQL Database is relational and requires a fixed schema, not suitable for varying JSON documents.
Azure Table Storage
Why wrong: Table Storage is key-value and does not support JSON document queries.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Azure Cosmos DB
Azure Cosmos DB is the correct choice because it provides native global distribution with multi-region writes and single-digit-millisecond latency at the 99th percentile, making it ideal for a mobile app requiring low-latency reads and writes worldwide. It natively supports JSON documents with varying schemas through its document model and offers multiple consistency levels to balance performance and data integrity.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Azure Cache for Redis
Why it's wrong here
Redis is a cache, not a durable primary data store.
Azure Cosmos DB
Why this is correct
Cosmos DB is a globally distributed NoSQL database with native JSON support and low-latency.
Related concept
Read the scenario before looking for a memorised answer.
Azure SQL Database
Why it's wrong here
Azure SQL Database is relational and requires a fixed schema, not suitable for varying JSON documents.
Azure Table Storage
Why it's wrong here
Table Storage is key-value and does not support JSON document queries.
Common exam traps
The trap here is that candidates often choose Azure Cache for Redis because they associate 'low-latency' with caching, but they overlook that the requirement is for a durable, globally distributed primary data store with varying JSON schemas, which Redis as a cache cannot fulfill as a persistent, globally writable database.
Detailed technical explanation
Cosmos DB achieves global low-latency through its multi-homing API and automatic, synchronous replication across Azure regions using a write-optimized, log-structured storage engine. Under the hood, it uses a resource-governed, multi-tenant architecture with partition-level replication, and the consistency model (e.g., bounded staleness, session) can be tuned per request to trade off between latency and read guarantees. In a real-world mobile app, this allows users in different continents to write and read the same data with sub-10ms latency while the service handles conflict resolution via last-writer-wins or custom conflict policies.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
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FAQ
Design data storage solutions — This question tests Design data storage solutions — Read the scenario before looking for a memorised answer..
The correct answer is: Azure Cosmos DB — Azure Cosmos DB is the correct choice because it provides native global distribution with multi-region writes and single-digit-millisecond latency at the 99th percentile, making it ideal for a mobile app requiring low-latency reads and writes worldwide. It natively supports JSON documents with varying schemas through its document model and offers multiple consistency levels to balance performance and data integrity.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This AZ-305 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the AZ-305 exam.
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