AZ-305 Design data storage solutions Practice Question
A company stores website static assets in Azure Blob Storage. The assets are updated weekly and must be available for immediate access for 30 days. After 30 days, older versions can be moved to the Cool tier to save costs but must still be accessible within seconds. They want an automated solution. What should they configure?
⚠ Common exam trap
Many candidates confuse Azure Policy (which enforces configuration at resource creation) with lifecycle management (which automates transitions based on time), leading candidates to choose Policy when only lifecycle rules can schedule tier changes.
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
✓
Use Azure Blob Storage lifecycle management rules
Azure Blob Storage lifecycle management rules allow you to automate tier transitions based on age or last modification time. By configuring a rule to move blobs to the Cool tier 30 days after creation, you meet the requirement for immediate access (Cool tier offers sub-second latency) while optimizing costs without manual intervention.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Set the access tier to Cool on the container
Why it's wrong here
Blob access tier is a property of an individual blob, not the container level; setting a container-wide tier would immediately force every blob to Cool regardless of its age, breaking the requirement that blobs under 30 days stay Hot. It also cannot be configured with a delay or condition based on last-modified time, so it must be applied per blob and does not scale to age-based transitions.
- ✓
Use Azure Blob Storage lifecycle management rules
Why this is correct
Azure Blob Storage lifecycle management lets you define JSON rules with a filter (e.g., prefix or blob index tag) and conditions using the age in days from last modification; setting daysAfterModificationGreaterThan: 30 with a tierToCool action automatically moves qualifying blobs to Cool while leaving newer blobs in Hot. The rule is evaluated asynchronously within 24 hours, which precisely satisfies the 30-day retention requirement without manual intervention or downtime.
- ✗
Manually change the access tier every 30 days
Why it's wrong here
Manually changing tiers every 30 days is a non-deterministic, ops-heavy process that requires custom scripts or portal clicks to scan all blobs, compute each blob's last-modified date, and update its tier one by one; any miss or timing mistake leaves blobs in the wrong tier or incurs write operation costs. Because the requirement is continuous and behavior-based, it cannot be reliably satisfied by periodic manual activity, while lifecycle rules provide a fully automated, policy-driven alternative.
- ✗
Use Azure Policy to enforce tier changes
Why it's wrong here
Azure Policy is a governance layer that enforces compliance by denying, auditing, or modifying resource properties at deployment time (e.g., requiring tags, restricting SKUs), but it cannot asynchronously evaluate the age of data or execute storage service actions like changing a blob's access tier after it has been written. Policies act on the ARM/Azure resource provider control plane, not on blob data plane objects, so they are irrelevant for automatic tier transitions based on last-modified timestamp.
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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