AZ-305 Design data storage solutions Practice Question
A company ingests IoT sensor data into Azure Blob Storage. Data is written frequently and is accessed rarely after the first 24 hours. The company must retain the data for exactly 90 days for compliance. They want to minimize storage costs by automatically moving data to the cheapest possible storage tier as soon as possible. Which Azure Blob Storage lifecycle management policy should they implement?
⚠ Common exam trap
Watch out — candidates often choose Archive tier thinking it is the cheapest, but they overlook the 180-day early deletion penalty and the fact that Cool tier is sufficient for 90-day retention with no penalty, making it the true cheapest option for this exact retention window.
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
✓
Move to Cool tier after 1 day, delete after 90 days
The data is rarely accessed after 24 hours, so moving it to Cool tier after 1 day minimizes cost while still allowing low-latency access. The 90-day deletion aligns with the compliance retention requirement. Cool tier is the cheapest online tier, and moving data there as soon as possible (after 1 day) reduces costs without incurring the early deletion penalty or retrieval latency of Archive tier.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Move to Cool tier after 1 day, delete after 90 days
Why this is correct
Moving the sensor data to the Cool tier after just one day aligns lifecycle costs with actual access patterns, since IoT telemetry is typically queried only briefly after ingestion. Cool tier provides significantly lower per-GB storage costs than Hot, and because the retention period of 90 days exceeds Cool's 30-day minimum commitment, no early deletion penalty is incurred. This policy satisfies the compliance requirement to delete after 90 days while minimizing the cost of storing data that is rarely read after the first 24 hours.
- ✗
Move to Archive tier after 1 day, delete after 90 days
Why it's wrong here
Selecting Archive after one day seems tempting for cost savings, but the Archive tier imposes a 180-day minimum retention period, so deleting after 90 days triggers an early deletion fee proportional to the remaining 90 days. While Archive has the lowest storage price, that price advantage is erased by this penalty, plus retrieval operations are more expensive and slower than Cool. The data does not need archival-grade long-term storage; it must simply be retained for 90 days, so Cool is the appropriate and cheaper choice.
- ✗
Move to Cool tier after 30 days, delete after 90 days
Why it's wrong here
Keeping data in the Hot tier for the first 30 days is unnecessary because data is rarely accessed after 24 hours. This results in higher costs for those 29 days compared to moving to Cool after 1 day.
- ✗
Move to Archive tier after 30 days, delete after 90 days
Why it's wrong here
Keeping the data in Hot for the first 30 days creates unnecessary cost, since the sensor readings are rarely accessed after the first day; this wastes approximately 29 days of Hot-tier pricing. Then moving to Archive for only 60 days still falls short of the 180-day minimum retention requirement, causing an early deletion charge that makes the total cost higher than a straightforward Cool-tier lifecycle. The combination of a Hot wait and an Archive penalty maximizes cost rather than minimizing it.
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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