AZ-900 Describe Azure architecture and services Practice Question
A company stores critical business data in an Azure Storage account. The data must remain available if a single Azure datacenter experiences a failure (e.g., fire, power outage). The company wants to minimize storage costs. Which storage redundancy option should they choose?
⚠ Common exam trap
It's easy for candidates to choose LRS because it is the cheapest option, forgetting that LRS does not protect against a full datacenter failure, which is explicitly required in the scenario.
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
✓
Zone-redundant storage (ZRS)
Zone-redundant storage (ZRS) synchronously replicates data across three Azure availability zones within a single region, ensuring data remains available if an entire datacenter fails. This meets the requirement for datacenter failure protection while minimizing costs compared to geo-redundant options, as ZRS does not incur cross-region bandwidth charges.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Locally redundant storage (LRS)
Why it's wrong here
Locally redundant storage (LRS) replicates each write three times synchronously within a single physical datacenter in the primary region. While this protects against individual disk or node failures, it cannot survive an entire datacenter outage—the exact failure scenario the company must guard against. Because LRS offers no cross-datacenter or cross-region redundancy, it is the least durable option and is unsuitable when datacenter-level availability is a requirement.
When this WOULD be correct
Choose LRS when the application can easily reconstruct data from other sources, or when data is non-critical and cost is the primary concern, and a single datacenter failure is acceptable (e.g., temporary test data).
- ✓
Zone-redundant storage (ZRS)
Why this is correct
ZRS replicates data across three Azure availability zones in the primary region. Each zone is an independent datacenter. This ensures data availability if one datacenter fails, and it is less expensive than geo-redundant storage because it does not use a secondary region.
- ✗
Geo-redundant storage (GRS)
Why it's wrong here
GRS replicates data to a secondary region that is hundreds of miles away, providing protection against a full regional outage. However, it is significantly more expensive than ZRS and the company only needs protection against a single datacenter failure, making ZRS a more cost-effective choice.
When this WOULD be correct
A company requires data to remain available during a region-wide disaster (e.g., a natural disaster affecting an entire Azure region) and can accept higher costs. In that scenario, GRS would be the correct choice because it replicates to a different region.
- ✗
Read-access geo-redundant storage (RA-GRS)
Why it's wrong here
RA-GRS provides the same geo-redundancy as GRS but also enables read access to the secondary region. It offers more durability than ZRS but at a higher cost. For the requirement of protecting against a single datacenter failure with minimal cost, ZRS is the optimal option.
When this WOULD be correct
A company needs to ensure data availability during a region-wide disaster (e.g., earthquake) and requires read access to the secondary copy for high availability, even if cost is a secondary concern.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The AZ-900 exam frequently reuses these exact scenarios with slightly different constraints.
✓Zone-redundant storage (ZRS)Correct answer▾
Why this is correct
ZRS replicates data across three Azure availability zones in the primary region. Each zone is an independent datacenter. This ensures data availability if one datacenter fails, and it is less expensive than geo-redundant storage because it does not use a secondary region.
✗Locally redundant storage (LRS)Wrong answer — click to see why▾
Why this is wrong here
LRS replicates data within a single datacenter, so it cannot survive a full datacenter failure (e.g., fire, power outage). The question requires availability across datacenter failures.
★ When this WOULD be the correct answer
Choose LRS when the application can easily reconstruct data from other sources, or when data is non-critical and cost is the primary concern, and a single datacenter failure is acceptable (e.g., temporary test data).
Why candidates choose this
Candidates may think LRS is sufficient because it provides local redundancy, and they overlook the requirement for datacenter-level failure protection, focusing only on cost minimization.
✗Geo-redundant storage (GRS)Wrong answer — click to see why▾
Why this is wrong here
GRS replicates data to a paired secondary region, which provides redundancy across regions but is more expensive than ZRS. The question requires resilience within a single datacenter failure and cost minimization, so ZRS (which replicates across zones within one region) is sufficient and cheaper.
★ When this WOULD be the correct answer
A company requires data to remain available during a region-wide disaster (e.g., a natural disaster affecting an entire Azure region) and can accept higher costs. In that scenario, GRS would be the correct choice because it replicates to a different region.
Why candidates choose this
Candidates may confuse 'datacenter failure' with 'region failure' and think GRS is needed for any failure, overlooking that ZRS already protects against a single datacenter outage at lower cost.
✗Read-access geo-redundant storage (RA-GRS)Wrong answer — click to see why▾
Why this is wrong here
RA-GRS provides geo-redundancy across regions, which is more expensive than ZRS and unnecessary for the requirement of surviving a single datacenter failure within the same region.
★ When this WOULD be the correct answer
A company needs to ensure data availability during a region-wide disaster (e.g., earthquake) and requires read access to the secondary copy for high availability, even if cost is a secondary concern.
Why candidates choose this
Candidates may confuse 'high availability' with 'disaster recovery' and assume that read access to a secondary region is needed, overlooking that the question only requires protection against a single datacenter failure.
Analysis generated from the official AZ-900blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
Go deeper
Related to this question
Learn chapter
Azure Regions and Geographies
Key term
Region
A region is a distinct geographic location where a cloud provider operates multiple data centers that are connected by low-latency networks and provide cloud services.
Key term
Storage account
A cloud storage account is a container that holds a set of cloud storage services and their data, providing a unique namespace and access policies for storing and managing unstructured data.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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