AZ-900 Describe Azure architecture and services Practice Question
A company stores a critical database in Azure Blob Storage. The data must remain available even if an entire Azure datacenter fails. The company uses the East US region, which supports availability zones. They want the lowest-cost storage redundancy option that protects against a full datacenter failure while keeping all data within the East US region. Which redundancy option should they choose?
⚠ Common exam trap
Watch out — candidates often confuse ZRS with GRS, thinking geo-redundancy is required for any datacenter failure, but the question explicitly limits data to the East US region, making ZRS the correct and lowest-cost option for intra-region datacenter failure protection.
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) is the correct choice because it synchronously replicates data across three availability zones within the East US region, ensuring data remains accessible even if an entire datacenter (one zone) fails. This meets the requirement for intra-region protection against a full datacenter failure at the lowest cost, as ZRS does not incur the additional expense of geo-replication.
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 your data three times synchronously within a single physical datacenter in the same region. While this protects against drive failures and rack-level issues, it provides no protection if the entire datacenter becomes unavailable—for example, due to a fire, flood, or network outage. Because the question explicitly requires the ability to withstand a datacenter failure, LRS fails that core requirement and is therefore incorrect.
When this WOULD be correct
A company needs the lowest-cost storage redundancy option and can tolerate a datacenter failure because they have a separate backup plan or the data is non-critical. The question would specify that only a single datacenter failure needs to be protected against, not a full datacenter failure.
- ✓
Zone-redundant storage (ZRS)
Why this is correct
ZRS replicates data synchronously across three Azure availability zones within the same region. Each availability zone is a separate datacenter. This protects against a single datacenter failure, keeps data within the East US region, and is less expensive than geo-redundant options. This meets all requirements.
- ✗
Geo-redundant storage (GRS)
Why it's wrong here
GRS replicates data to a secondary region that is geographically paired (e.g., East US pairs with West US). While it protects against a regional disaster, it copies data outside the East US region, which may increase cost and is not necessary for the stated requirement of staying within the single region.
When this WOULD be correct
A company requires data to survive a region-wide disaster (e.g., both datacenters in East US fail) and is willing to store data in a secondary region. They need the lowest-cost option that provides cross-region redundancy without read access to the secondary copy.
- ✗
Read-access geo-redundant storage (RA-GRS)
Why it's wrong here
RA-GRS is identical to GRS but also provides read access to the secondary region. Like GRS, it replicates data to a different region, which is not required and incurs additional cost. It does not meet the 'within East US' constraint.
When this WOULD be correct
A company needs to ensure data is available even if an entire region fails, and they require read access to the secondary copy at all times. They are willing to pay more for geo-replication and accept data residency across regions.
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 within the same region. Each availability zone is a separate datacenter. This protects against a single datacenter failure, keeps data within the East US region, and is less expensive than geo-redundant options. This meets all requirements.
✗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 protect against an entire datacenter failure, which is the requirement in the question.
★ When this WOULD be the correct answer
A company needs the lowest-cost storage redundancy option and can tolerate a datacenter failure because they have a separate backup plan or the data is non-critical. The question would specify that only a single datacenter failure needs to be protected against, not a full datacenter failure.
Why candidates choose this
Candidates may choose LRS because it is the cheapest option and they overlook the requirement for protection against a full datacenter failure, assuming that 'lowest-cost' is the primary driver without considering the redundancy need.
✗Geo-redundant storage (GRS)Wrong answer — click to see why▾
Why this is wrong here
GRS replicates data to a paired secondary region (e.g., West US), which increases cost and may place data outside East US, violating the requirement to keep all data within East US.
★ When this WOULD be the correct answer
A company requires data to survive a region-wide disaster (e.g., both datacenters in East US fail) and is willing to store data in a secondary region. They need the lowest-cost option that provides cross-region redundancy without read access to the secondary copy.
Why candidates choose this
Candidates may confuse 'full datacenter failure' with 'full region failure' and think GRS is needed for any failure beyond a single datacenter, overlooking that ZRS already protects against datacenter failure within the same region.
✗Read-access geo-redundant storage (RA-GRS)Wrong answer — click to see why▾
Why this is wrong here
RA-GRS replicates data to a secondary region (geo-replication), which violates the requirement to keep all data within the East US region. It also costs more than ZRS, which meets the requirement at lower cost.
★ When this WOULD be the correct answer
A company needs to ensure data is available even if an entire region fails, and they require read access to the secondary copy at all times. They are willing to pay more for geo-replication and accept data residency across regions.
Why candidates choose this
Candidates may think RA-GRS provides the highest availability and mistakenly believe it is the cheapest option that protects against datacenter failure, overlooking the requirement to stay within a single region.
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?”
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 |
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
Courseiva writes every AZ-900 question from scratch — 981 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
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.