AZ-900 Describe Azure architecture and services Practice Question
Which Azure storage redundancy option replicates data synchronously across three availability zones within a single region?
⚠ Common exam trap
It's easy for candidates to confuse ZRS with LRS, thinking LRS provides zone-level redundancy, but LRS only replicates within a single datacenter and does not protect against zone failures.
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 answer because it synchronously replicates data across three Azure availability zones within a single region, ensuring high durability and availability even if an entire zone fails. This meets the exact requirement of the question: synchronous replication across multiple zones in one region.
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) is incorrect because it replicates data three times within a single datacenter in the same region. LRS protects against server and disk failures within that datacenter but does not protect against an entire availability zone outage, as all copies are located in the same physical facility. Therefore, LRS cannot meet a requirement for availability-zone redundancy.
- ✓
Zone-Redundant Storage (ZRS)
Why this is correct
Zone-Redundant Storage (ZRS) is correct because it synchronously replicates data across three availability zones within a single region. This design allows storage accounts to remain available even if an entire availability zone fails, without requiring a failover to a different region. The synchronous write ensures durability and consistency across all three copies, making ZRS the specific redundancy tier that meets the described requirement.
- ✗
Geo-Redundant Storage (GRS)
Why it's wrong here
Geo-Redundant Storage (GRS) is incorrect because it provides geo-replication to a paired secondary region but relies on Locally Redundant Storage (LRS) in the primary region, meaning data is only copied within a single datacenter in the primary. If the question's requirement is to survive an availability zone outage, GRS alone would not protect against that failure in the primary region. The asynchronous copy to the secondary region does not provide synchronous availability-zone redundancy, so GRS does not satisfy the stated condition.
- ✗
Geo-Zone-Redundant Storage (GZRS)
Why it's wrong here
Geo-Zone-Redundant Storage (GZRS) is incorrect because it extends beyond the stated requirement: it synchronously replicates data across three availability zones in the primary region AND asynchronously replicates to a secondary region. While GZRS does provide zone redundancy, the extra geo-replication makes it a more expensive and more complex solution than needed when the question only asks for replication across availability zones. Therefore, GZRS is not the best or correct answer.
Go deeper
Related to this question
Learn chapter
Azure Regions and Geographies
Key term
Availability
Availability is the measure of how often a system or service is operational and accessible when needed, typically expressed as a percentage of uptime.
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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