AZ-900 Describe Azure architecture and services Practice Question
A company is deploying a business-critical application on Azure virtual machines in the East US region. The application's managed disks must remain available even if an entire Azure datacenter experiences an outage. The company does not require cross-region disaster recovery. Which storage redundancy option should they select for the managed disks?
⚠ Common exam trap
Many exam-takers choose LRS thinking it provides sufficient redundancy for high availability, but they overlook that LRS protects only against local hardware failures within a single datacenter, not an entire datacenter outage.
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 the East US region, ensuring the managed disks remain available even if an entire datacenter (one zone) fails. This meets the requirement for intra-region resilience without needing cross-region disaster recovery.
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
LRS replicates data three times within a single datacenter. This protects against hardware failures within the datacenter but does not protect against an entire datacenter outage. Therefore, it would not meet the requirement for availability if a datacenter fails.
When this WOULD be correct
A company needs cost-effective storage for non-critical data that can tolerate a single server or rack failure, and does not require availability during a datacenter outage. For example, dev/test environments or temporary data where low cost is prioritized over high availability.
- ✓
Zone-Redundant Storage (ZRS)
Why this is correct
ZRS replicates data synchronously across three Azure availability zones in the same region. If one zone (datacenter) goes down, the data remains available from the other zones. This is the correct choice for ensuring that managed disks survive a full datacenter failure within a single region.
- ✗
Geo-Redundant Storage (GRS)
Why it's wrong here
GRS replicates data to a secondary region for disaster recovery. However, GRS is not supported for Azure managed disks. It is designed for Azure storage accounts (blobs, files, queues, tables). Additionally, the requirement is only for within-region availability, not cross-region, so GRS would be overkill and unsupported.
When this WOULD be correct
A company requires data to remain available even if an entire Azure region experiences an outage, and they need cross-region disaster recovery. For example, a global e-commerce platform must ensure data durability and availability during a regional disaster.
- ✗
Read-Access Geo-Redundant Storage (RA-GRS)
Why it's wrong here
RA-GRS is similar to GRS but also allows read access to the data in the secondary region. Like GRS, it is not available for managed disks and is intended for storage accounts. It also provides cross-region protection, which is not needed here.
When this WOULD be correct
A company requires high availability for a storage account that must remain accessible even if the primary region becomes unavailable, and they need read access to the data in the secondary region during an outage. For example, a global application serving read-heavy traffic that can tolerate eventual consistency.
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 synchronously across three Azure availability zones in the same region. If one zone (datacenter) goes down, the data remains available from the other zones. This is the correct choice for ensuring that managed disks survive a full datacenter failure within a single 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 an entire datacenter outage. The question requires availability even if a full datacenter fails, which ZRS provides by replicating across multiple zones.
★ When this WOULD be the correct answer
A company needs cost-effective storage for non-critical data that can tolerate a single server or rack failure, and does not require availability during a datacenter outage. For example, dev/test environments or temporary data where low cost is prioritized over high availability.
Why candidates choose this
Candidates may confuse 'redundancy' with 'availability' and think LRS is sufficient because it protects against local hardware failures, overlooking the requirement for datacenter-level outage protection.
✗Geo-Redundant Storage (GRS)Wrong answer — click to see why▾
Why this is wrong here
Geo-Redundant Storage (GRS) replicates data to a paired secondary region, which provides cross-region disaster recovery. The question explicitly states the company does not require cross-region disaster recovery, so GRS is unnecessary and more expensive than needed.
★ When this WOULD be the correct answer
A company requires data to remain available even if an entire Azure region experiences an outage, and they need cross-region disaster recovery. For example, a global e-commerce platform must ensure data durability and availability during a regional disaster.
Why candidates choose this
Candidates may think GRS offers the highest availability and automatically choose it for critical applications, overlooking the specific requirement that cross-region recovery is not needed.
✗Read-Access Geo-Redundant Storage (RA-GRS)Wrong answer — click to see why▾
Why this is wrong here
RA-GRS provides cross-region replication to a secondary region, but the question explicitly states no cross-region disaster recovery is required. The requirement is to survive an entire datacenter outage within a single region, which ZRS handles by replicating across availability zones.
★ When this WOULD be the correct answer
A company requires high availability for a storage account that must remain accessible even if the primary region becomes unavailable, and they need read access to the data in the secondary region during an outage. For example, a global application serving read-heavy traffic that can tolerate eventual consistency.
Why candidates choose this
Candidates may confuse 'datacenter outage' with 'regional outage' and think RA-GRS offers higher durability, overlooking the explicit constraint against cross-region disaster recovery in the question.
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?”
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
Zone-redundant storage
Zone-redundant storage is a data replication method that stores copies of your data in multiple physical locations within a cloud region, so your data remains safe and available even if one entire data center fails.
About these practice questions
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This AZ-900 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the AZ-900 exam.