AZ-900 Describe Azure architecture and services Practice Question
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?
⚠ Common exam trap
Many candidates confuse 'surviving a datacenter failure' with needing geo-redundancy, but ZRS within the same region is sufficient and avoids the latency penalty of cross-region replication.
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 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.
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) copies data three times synchronously within a single physical datacenter in the primary region. This protects against disk and server failures within that datacenter, but if the entire datacenter—due to fire, flooding, or other disasters—becomes unavailable, all three replicas are lost simultaneously. Therefore, LRS is the cheapest replication option but does not meet the resilience needs of healthcare data, where availability and recovery are critical.
When this WOULD be correct
LRS would be correct if the requirement was to protect against local hardware failures (e.g., disk or server failures) within a single datacenter, with no need for cross-datacenter or cross-region redundancy.
- ✓
Zone-Redundant Storage (ZRS)
Why this is correct
Zone-Redundant Storage (ZRS) replicates data synchronously across three Azure availability zones within the primary region. Each zone is an independent datacenter (or set of datacenters) with separate power, cooling, and networking, so if one zone goes down, the data remains available and durable in the other two. ZRS provides high availability with no data loss during zone failures, and because all zones are in the same region, write latency remains low for applications that must access patient records quickly. Unlike LRS, ZRS protects against entire datacenter outages, and unlike GRS/RA-GRS, it does not add the latency of cross-region replication.
- ✗
Geo-Redundant Storage (GRS)
Why it's wrong here
Geo-Redundant Storage (GRS) replicates data to a secondary region that is hundreds of miles away from the primary region, offering geographic redundancy against region-wide disasters. However, GRS is asynchronous, meaning there is a window (typically up to 15 minutes) during which recently written data may not have reached the secondary copy and could be lost in a regional failure. Additionally, GRS does not provide read access to the secondary copy unless failover is initiated, and the distance introduces significant latency for any cross-region operations—making it unsuitable for the stated requirement of same-region resilience with low latency.
When this WOULD be correct
A company needs to protect against a region-wide disaster (e.g., a natural disaster affecting an entire Azure region) and requires data to be durable across two geographically separated regions. The question would specify that data must survive a regional outage, not just a datacenter failure.
- ✗
Read-Access Geo-Redundant Storage (RA-GRS)
Why it's wrong here
Read-Access Geo-Redundant Storage (RA-GRS) replicates data asynchronously to a paired secondary region and also enables read access from that secondary region. While RA-GRS provides read access to the secondary copy during an outage, the secondary region is geographically distant, and because replication is asynchronous, writes made before a failover could be lost if the primary region fails. The question explicitly specifies 'within the same region,' which RA-GRS does not satisfy; it is designed for disaster recovery across regions, not for low-latency same-region zone redundancy.
When this WOULD be correct
A company needs data to remain available even if an entire Azure region fails, and they require read access to the secondary region at all times. In that scenario, RA-GRS is correct because it provides geo-redundancy with read access to the secondary copy.
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
Zone-Redundant Storage (ZRS) replicates data synchronously across three Azure availability zones within the primary region. Each zone is an independent datacenter (or set of datacenters) with separate power, cooling, and networking, so if one zone goes down, the data remains available and durable in the other two. ZRS provides high availability with no data loss during zone failures, and because all zones are in the same region, write latency remains low for applications that must access patient records quickly. Unlike LRS, ZRS protects against entire datacenter outages, and unlike GRS/RA-GRS, it does not add the latency of cross-region replication.
✗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 a key requirement in the question.
★ When this WOULD be the correct answer
LRS would be correct if the requirement was to protect against local hardware failures (e.g., disk or server failures) within a single datacenter, with no need for cross-datacenter or cross-region redundancy.
Why candidates choose this
Candidates may confuse LRS as sufficient because it provides local redundancy, overlooking the requirement for datacenter-level failure protection.
✗Geo-Redundant Storage (GRS)Wrong answer — click to see why▾
Why this is wrong here
Geo-Redundant Storage (GRS) replicates data to a secondary region, which does not guarantee availability within the same region for low latency; it also fails to protect against a full datacenter failure within the primary region without relying on the secondary region.
★ When this WOULD be the correct answer
A company needs to protect against a region-wide disaster (e.g., a natural disaster affecting an entire Azure region) and requires data to be durable across two geographically separated regions. The question would specify that data must survive a regional outage, not just a datacenter failure.
Why candidates choose this
Candidates may confuse 'geo-redundant' with 'zone-redundant' or think that any redundancy option with 'redundant' in the name provides high availability, overlooking the specific requirement for intra-region datacenter failure protection.
✗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 for disaster recovery, but it does not guarantee availability within the same region during a datacenter failure; it is designed for region-level failures, not datacenter-level failures within a region.
★ When this WOULD be the correct answer
A company needs data to remain available even if an entire Azure region fails, and they require read access to the secondary region at all times. In that scenario, RA-GRS is correct because it provides geo-redundancy with read access to the secondary copy.
Why candidates choose this
Candidates may confuse 'read-access' with high availability and think that RA-GRS offers better availability than ZRS, not realizing that RA-GRS is for region-level failures, not datacenter failures within a 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
Blob storage
Blob storage is a cloud service for storing large amounts of unstructured data, such as text or binary data, like documents, images, and videos.
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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