DP-900 Describe core data concepts Practice Question
A company wants to store JSON documents from IoT devices with low latency and high availability. Which Azure data store should they use?
⚠ Common exam trap
A common mix-up: candidates confuse Azure Blob Storage's ability to store JSON files with the need for a database that can natively query and index JSON documents, leading them to choose Blob Storage for its low cost rather than Cosmos DB for its low-latency querying capabilities.
Answer choices
Why each option matters
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 is a fully managed NoSQL database designed for low-latency, high-availability workloads, with native support for JSON documents. It offers single-digit millisecond read/write latencies at the 99th percentile, global distribution with multi-region writes, and multiple consistency models, making it ideal for IoT scenarios that require fast, always-on access to semi-structured data.
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 Blob Storage
Why it's wrong here
Azure Blob Storage can store JSON files as opaque blobs, but it is not a queryable data store: there is no native indexing or query engine for JSON properties, so you must download each blob and parse it client-side. Because IoT scenarios rely on efficient lookups and filtering by document fields, Blob Storage alone would force full-file reads and manual processing, making it unsuitable for the stated requirement.
- ✓
Azure Cosmos DB
Why this is correct
Azure Cosmos DB is a globally distributed, multi-model NoSQL database with native JSON document support, meaning JSON objects are stored as-is and every property is automatically indexed for querying. It provides single-digit-millisecond reads and writes at any scale via request-unit throughput, making it ideal for high-ingestion IoT workloads that need to query device JSON documents with low latency.
- ✗
Azure Table Storage
Why it's wrong here
Azure Table Storage is a schema-less key-value store where data is stored as a collection of entities composed of partition keys, row keys, and typed properties, not as raw JSON documents. Although you can serialize JSON into a property, you cannot natively query inside nested JSON structures, and entity payloads are capped at 1 MB, so it is a poor fit for storing IoT JSON documents that need document-level querying.
- ✗
Azure SQL Database
Why it's wrong here
Azure SQL Database can store JSON as text in an NVARCHAR column and uses JSON_VALUE/OPENJSON functions to query it, but this is a relational engine bolted onto documents, not a native document database. IoT JSON tends to have variable schemas and high write volumes, which fit poorly with fixed relational schemas and provisioned compute; Cosmos DB is better suited for fast, schema-agnostic JSON handling.
Go deeper
Related to this question
Learn chapter
Data Roles and Core Concepts
Key term
Data
Data is raw, unprocessed information, like numbers, words, or measurements, that can be stored, processed, and analyzed by computers.
Key term
Structured data
Structured data is information that is organized in a predefined format, typically in rows and columns, making it easy to search, process, and analyze by computers.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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