ZRS: Protect Against Datacenter Failure Within a Region
A company stores compliance logs in Azure Blob Storage. The logs must remain available even if an entire Azure datacenter within the primary region fails. The company is cost-conscious and wants to minimize storage costs while meeting this availability requirement. The company does not need to access the data from a secondary location during a disaster. Which storage replication option should the company choose?
Quick Answer
The correct choice is Zone-redundant storage (ZRS). ZRS replicates your data synchronously across three separate Azure availability zones within a single region, so if an entire datacenter—which corresponds to one zone—fails, your compliance logs remain available without interruption. This meets the requirement for protection against a datacenter failure within the primary region while keeping costs lower than geo-redundant options, since you are not paying for cross-region replication. On the AZ-900 exam, this scenario tests your understanding of how ZRS balances high availability and cost; a common trap is choosing Geo-redundant storage (GRS) because it also offers durability, but GRS is more expensive and provides secondary region access that the company explicitly does not need. Remember the memory tip: “ZRS = Zone Redundancy, Same Region” — if you only need to survive a datacenter failure locally and want to save money, ZRS is your zone-based shield.
⚠ Common exam trap
A common mix-up: candidates choose LRS thinking it is cheapest, but they overlook that LRS cannot survive a full datacenter failure, while ZRS provides the required availability at minimal additional cost.
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) replicates data synchronously across three Azure availability zones within the primary region. This ensures data remains available even if an entire datacenter (one zone) fails, while avoiding the higher cost and cross-region replication of GRS. Since the company does not need secondary region access and wants to minimize costs, ZRS meets the requirement without paying for geo-redundancy.
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 physical datacenter in the primary region. If the entire datacenter fails, the data is lost. LRS does not meet the requirement to survive a datacenter failure.
When this WOULD be correct
If the requirement were only to protect against a single server or disk failure within a datacenter, and cost minimization was the top priority, LRS would be the correct choice.
- ✓
Zone-redundant storage (ZRS)
Why this is correct
ZRS replicates data synchronously across three Azure availability zones within the primary region. Each zone is a physically separate datacenter (or multiple datacenters) with independent power and networking. This protects against the failure of a single datacenter. ZRS is more expensive than LRS but less expensive than geo-redundant options, making it the most cost-effective choice for this requirement.
- ✗
Geo-redundant storage (GRS)
Why it's wrong here
GRS replicates data to a secondary region that is hundreds of kilometers apart. While this provides region-level disaster recovery, it is more expensive than ZRS. The company only needs protection within the primary region, so GRS is unnecessarily costly and does not offer a cost advantage.
When this WOULD be correct
GRS would be correct if the question required data to remain available even during a region-wide disaster (e.g., entire primary region failure) and the company needed the ability to fail over to a secondary region, even if not accessed during normal operations.
- ✗
Read-access geo-redundant storage (RA-GRS)
Why it's wrong here
RA-GRS includes all the features of GRS plus read access to the secondary region. This is even more expensive than GRS and provides functionality (reading from secondary) that the company explicitly does not require. It is not the most cost-effective option for the stated need.
When this WOULD be correct
A company requires data to remain available even if an entire region fails, and they need to be able to read the data from the secondary region immediately during a disaster (e.g., for business continuity or disaster recovery). The company is willing to pay higher costs for this capability.
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 primary region. Each zone is a physically separate datacenter (or multiple datacenters) with independent power and networking. This protects against the failure of a single datacenter. ZRS is more expensive than LRS but less expensive than geo-redundant options, making it the most cost-effective choice for this requirement.
✗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 failure, which is required by the question.
★ When this WOULD be the correct answer
If the requirement were only to protect against a single server or disk failure within a datacenter, and cost minimization was the top priority, LRS would be the correct choice.
Why candidates choose this
Candidates may choose LRS because it is the cheapest option and they overlook the requirement for datacenter-level failure protection, focusing only on cost.
✗Geo-redundant storage (GRS)Wrong answer — click to see why▾
Why this is wrong here
GRS replicates data to a secondary region, which incurs higher costs and provides geo-redundancy beyond the requirement of surviving a single datacenter failure within the primary region. The question specifies no need for secondary region access, making ZRS (which replicates across zones within one region) the cost-effective choice.
★ When this WOULD be the correct answer
GRS would be correct if the question required data to remain available even during a region-wide disaster (e.g., entire primary region failure) and the company needed the ability to fail over to a secondary region, even if not accessed during normal operations.
Why candidates choose this
Candidates may confuse 'surviving a datacenter failure' with needing geo-redundancy, or they may overestimate the required durability and choose GRS as a 'safer' option without considering cost constraints.
✗Read-access geo-redundant storage (RA-GRS)Wrong answer — click to see why▾
Why this is wrong here
RA-GRS provides read access to data in a secondary region, but the question states the company does not need to access data from a secondary location during a disaster. Additionally, RA-GRS is more expensive than ZRS, contradicting the cost-conscious requirement.
★ When this WOULD be the correct answer
A company requires data to remain available even if an entire region fails, and they need to be able to read the data from the secondary region immediately during a disaster (e.g., for business continuity or disaster recovery). The company is willing to pay higher costs for this capability.
Why candidates choose this
Candidates may think RA-GRS offers the highest availability and automatically assume it's the best choice, overlooking the specific requirement that secondary access is not needed and that cost must be minimized.
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
Azure datacenter
An Azure datacenter is a physical facility that houses Microsoft's cloud computing infrastructure, including servers, storage, and networking equipment, to deliver Azure services globally.
Key term
Blob
A blob is a large piece of unstructured data, like a photo or video, stored in the cloud with a unique identifier.
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Same concept, more angles
2 more ways this is tested on AZ-900
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. 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?
medium- A.Locally redundant storage (LRS)
- ✓ B.Zone-redundant storage (ZRS)
- C.Geo-redundant storage (GRS)
- D.Read-access geo-redundant storage (RA-GRS)
Why B: 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.
Variation 2. A healthcare organization stores patient records in Azure Blob Storage. They require that data remains available even if an entire Azure datacenter fails, and they also need to ensure data is replicated within the same region for low latency. Which storage redundancy option should they choose?
hard- A.Locally Redundant Storage (LRS)
- ✓ B.Zone-Redundant Storage (ZRS)
- C.Geo-Redundant Storage (GRS)
- D.Read-Access Geo-Redundant Storage (RA-GRS)
Why B: Zone-Redundant Storage (ZRS) synchronously replicates data across three Azure availability zones within the same region, ensuring data remains available even if an entire datacenter (one zone) fails. This meets both the availability requirement and the low-latency requirement because replication stays within the region, avoiding cross-region latency.
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.