DP-203 Design and implement data storage Practice Question
A company is designing a data storage solution for IoT device telemetry data. The data is append-only, needs to be stored cost-effectively for long-term analytics, and must support querying by device ID and timestamp. Which Azure storage solution should they use?
⚠ Common exam trap
Candidates often confuse Azure Blob Storage with ADLS Gen2, assuming that Blob Storage alone supports hierarchical namespace and efficient querying, when in fact ADLS Gen2 is required for the hierarchical namespace and POSIX-like directory structure that enables partition pruning and cost-effective analytics on append-only data.
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 Data Lake Storage Gen2
Azure Data Lake Storage Gen2 (ADLS Gen2) is the correct choice because it combines the cost-effective, append-only blob storage of Azure Blob Storage with a hierarchical namespace that enables directory-level operations and POSIX-like access control. This makes it ideal for storing large volumes of IoT telemetry data at low cost while supporting efficient querying by device ID and timestamp through partition pruning in tools like Azure Synapse Analytics or Apache Spark.
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 Data Lake Storage Gen2
Why this is correct
Azure Data Lake Storage Gen2 suits append-only telemetry because its hierarchical namespace organises data into directories partitioned by device ID and timestamp, enabling efficient partition pruning during analytics queries. It also layers the cost-effective Hot, Cool and Archive tiers over Blob storage, satisfying the long-term retention requirement without sacrificing query performance.
- ✗
Azure Cosmos DB
Why it's wrong here
Cosmos DB bills provisioned or serverless request units plus storage, making long-term retention of high-volume telemetry expensive. It is tempting because it indexes device ID and timestamp efficiently for queries, but the cost-effective long-term storage requirement points to Blob Storage instead.
- ✗
Azure SQL Database
Why it's wrong here
Azure SQL Database is a relational engine with provisioned compute and per-GB pricing, so it cannot store append-only telemetry cost-effectively at scale. It is tempting because SQL queries by device ID and timestamp are natural, but the cost and volume requirements rule out a transactional database.
- ✗
Azure Blob Storage with hot access tier
Why it's wrong here
The hot tier stores frequently accessed data at the highest per-GB cost, contradicting the long-term cost-effective requirement; Blob Storage's archive or cool tiers fit instead. Hot is tempting because Blob Storage itself suits append-only telemetry, but the tier choice breaks the cost constraint.
Quick reference
Azure Blob Storage Tier Comparison
| Tier | Storage Cost | Retrieval Cost | Latency | Use Case |
|---|---|---|---|---|
| Hot | Highest | Lowest | Immediate | Active data, frequent reads |
| Cool | Lower | Higher | Immediate | Data accessed < once / month |
| Cold | Lower still | Higher | Immediate | Data accessed < once / quarter |
| Archive | Lowest | Highest + rehydration delay | Hours | Long-term compliance retention |
Go deeper
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Key term
Azure Synapse Analytics
Azure Synapse Analytics is a cloud-based data integration, warehousing, and analytics service that brings together big data and data warehouse capabilities under one platform.
Key term
Azure Data Lake Gen2
Azure Data Lake Gen2 is a cloud-based data storage service that combines the scalability and performance of a data lake with the hierarchical file system and security of a data warehouse, designed for big data analytics.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DP-203 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 DP-203 exam.