AZ-305 Design infrastructure solutions Practice Question
You need to design a storage solution for an application that stores large amounts of unstructured data that is accessed frequently for the first 30 days, then rarely after that. Compliance requirements mandate that data be retained for 7 years. Which of the following is the most cost-effective storage solution?
⚠ Common exam trap
Many candidates choose Azure Files or Managed Disks because they associate 'storage' with file shares or disks, but Blob Storage's tiered lifecycle management is the only option that provides automated, cost-optimized transitions for unstructured data with long-term retention.
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 with lifecycle management to transition blobs from Hot to Cool to Archive tiers.
Azure Blob Storage lifecycle management allows you to automatically transition blobs from Hot to Cool after 30 days (once the initial frequent access period ends), and then to Archive after an additional period of low access (e.g., another 30 days) to meet the 7-year retention requirement at the lowest cost. The Archive tier provides the cheapest storage for rarely accessed data, while Hot and Cool tiers optimize for the initial high-access period.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use Azure Files with snapshots and keep files in the Premium tier for 30 days, then move to Standard tier.
Why it's wrong here
Azure Files is a managed file share service providing SMB and NFS protocols, intended for lift-and-shift file servers or shared folders, not for storing tens of millions of unstructured blobs. While you can take snapshots, they are point-in-time read-only copies that do not automate tiering, and moving a share from Premium to Standard requires copying data rather than seamless lifecycle transitions. Premium file shares are also billed per GiB/month with higher per-operation costs, making them far more expensive than Blob Storage for long-term retention.
- ✗
Use Azure Managed Disks with read-only snapshots and delete snapshots after 7 years.
Why it's wrong here
Azure Managed Disks are block-level storage volumes attached to virtual machines, with a maximum size of 32 TiB per disk, and their snapshots are incremental, capturing only changed blocks since the last snapshot. These snapshots are designed for disk backup and restoration, not as an independent object store; accessing data from them requires mounting or restoring the disk to a VM, which is impractical for application-level data retrieval over 7 years. Additionally, maintaining a chain of incremental snapshots for 7 years incurs significant storage costs and operational complexity, and the data is not natively addressable via REST APIs.
- ✓
Use Azure Blob Storage with lifecycle management to transition blobs from Hot to Cool to Archive tiers.
Why this is correct
Azure Blob Storage is purpose-built for massive amounts of unstructured object data, offering essentially limitless scale and REST-based access. Lifecycle management lets you define rules to automatically move blobs from Hot to Cool after a set number of days based on last modification, and then from Cool to Archive after a longer period, which optimizes cost while preserving all data. Archive tier provides the lowest storage price for rarely accessed data, and with rehydration you can still retrieve it when needed, making this the most scalable and cost-effective design for long-term retention.
- ✗
Store all data in Blob Storage Hot tier and delete after 7 years.
Why it's wrong here
Keeping everything in the Hot tier for 7 years is extremely inefficient because Hot tier has the highest per-GiB storage price and is intended for frequent access, while the application's data likely becomes cold and rarely read after the initial upload. Deleting the data after 7 years does nothing to reduce the substantial cost incurred during years 2 through 7 when the data is dormant. Azure Blob Storage's Archive tier offers storage at a fraction of Hot's price, and lifecycle management can move the data automatically, so you should not keep it exclusively in Hot.
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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