DP-203 Design and implement data storage Practice Question
A data engineer needs to store semi-structured JSON log files from a web application. Each log entry is about 1 KB. The logs are rarely queried (once a month) and must be retained for 7 years for compliance. The solution must minimize storage cost. Which storage option should be used?
⚠ Common exam trap
It's easy for candidates to choose Azure Cosmos DB (D) because it natively supports JSON, but they overlook the extreme cost of storing and rarely querying 7 years of data in a globally distributed, high-throughput NoSQL database, which is optimized for frequent, low-latency access, not archival.
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
✓
Store the logs in Azure Blob Storage with cool access tier.
Azure Blob Storage with the cool access tier is the correct choice because it is optimized for storing large amounts of semi-structured data (like JSON logs) at low cost, with infrequent access (once a month) and long retention (7 years). The cool tier offers lower storage costs than hot or premium tiers, while still providing high durability and the ability to query logs using tools like Azure Data Lake Storage or serverless SQL. This meets the compliance requirement without the high compute or transaction costs of a database solution.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Store the logs in Azure SQL Database as a table.
Why it's wrong here
SQL Database is expensive for large volumes of rarely queried data.
- ✗
Store the logs in Azure Files share.
Why it's wrong here
Azure Files is more expensive and designed for file shares, not log archiving.
- ✓
Store the logs in Azure Blob Storage with cool access tier.
Why this is correct
Blob Storage cool tier is low-cost for infrequent access, suitable for logs.
- ✗
Store the logs in Azure Cosmos DB with a JSON container.
Why it's wrong here
Cosmos DB is expensive for infrequent access and large retention.
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 |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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