Quick Answer
Azure Cosmos DB is the correct choice because it serves as a globally distributed key-value store with sub-millisecond read and write latencies, meeting the application’s need for high availability across multiple Azure regions without complex query support. Its turnkey global distribution enables active-active replication, allowing data to be written and read from any region with guaranteed single-digit millisecond latency at the 99th percentile, while multiple consistency models like eventual consistency can further optimize performance. On the AZ-305 exam, this scenario tests your ability to match workload requirements to the right data store, often contrasting Cosmos DB’s key-value API with alternatives like Azure Table Storage or Redis Cache—a common trap is choosing Redis for low latency but forgetting its lack of native multi-region write support. Remember the mnemonic “Cosmos Covers Key-Value Globally” to recall that Cosmos DB is the only Azure service offering turnkey global distribution with sub-10-ms latency for simple key-value workloads.
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.
An application requires a highly available key-value store with sub-millisecond read and write latencies across multiple Azure regions. The data model is simple and does not require complex queries. Which Azure data store should they choose?
Azure SQL Database
Why wrong: Relational, not optimized for key-value.
Azure Table Storage
Why wrong: No multi-region writes, higher latency.
Azure Cosmos DB
Globally distributed, low-latency key-value store.
Azure Cache for Redis
Why wrong: Not a persistent data store.
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 a globally distributed, multi-region key-value store with guaranteed sub-10-millisecond read and write latencies at the 99th percentile, and supports multiple consistency models including eventual consistency for even lower latency. Its turnkey global distribution enables active-active replication across Azure regions, meeting the high availability and sub-millisecond performance requirements without complex query support.
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 SQL Database
Why it's wrong here
Relational, not optimized for key-value.
Azure Table Storage
Why it's wrong here
No multi-region writes, higher latency.
Azure Cosmos DB
Why this is correct
Globally distributed, low-latency key-value store.
Related concept
Read the scenario before looking for a memorised answer.
Azure Cache for Redis
Why it's wrong here
Not a persistent data store.
Common exam traps
The trap here is that candidates often confuse Azure Cache for Redis as a primary data store due to its sub-millisecond performance, but it lacks global distribution and durability guarantees, making Cosmos DB the correct choice for a highly available, multi-region key-value store.
Detailed technical explanation
Cosmos DB achieves sub-millisecond latencies by using a write-optimized, log-structured B-tree index and partitioning data across physical replicas with automatic indexing. Its multi-region writes rely on a conflict resolution mechanism (e.g., last-writer-wins or custom) to handle concurrent updates, and the consistency level can be tuned from eventual to strong, with eventual providing the lowest latency. In a real-world scenario, a global e-commerce cart service would use Cosmos DB with multi-region writes to ensure users in different continents see consistent cart data with minimal delay.
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 a globally distributed, multi-region key-value store with guaranteed sub-10-millisecond read and write latencies at the 99th percentile, and supports multiple consistency models including eventual consistency for even lower latency. Its turnkey global distribution enables active-active replication across Azure regions, meeting the high availability and sub-millisecond performance requirements without complex query support.
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
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