Azure Storage offers several replication strategies to ensure data durability, availability, and high performance.
These strategies determine how and where your data is copied to protect against data loss and provide redundancy.
Here's an overview.
Locally Redundant Storage (LRS)
Description
Data is replicated three times within a single physical location in the same Azure region.
Use Case
Suitable for scenarios where cost is a priority and data doesn't need to be resilient to datacenter failures.
Durability
11 nines (99.999999999%) over a given year.
Zone-Redundant Storage (ZRS)
Description
Data is replicated across three availability zones in the same Azure region.
Use Case
Ideal for high availability within a region and protection against a zonal failure.
Durability
12 nines (99.9999999999%) over a year.
Scenarios
Recommended for read-intensive workloads requiring higher availability.
Geo-Redundant Storage (GRS)
Description
Data is replicated to a secondary region hundreds of miles away from the primary region for disaster recovery.
Three replicas are kept in the primary region (like LRS).
Three replicas are maintained asynchronously in the secondary region.
Use Case
Suitable for disaster recovery scenarios.
Durability
16 nines (99.99999999999999%) over a year.
Read Access
Access to the secondary region is unavailable unless Microsoft initiates a failover.
Read-Access Geo-Redundant Storage (RA-GRS)
Description
Like GRS but provides read-only access to the data in the secondary region.
Use Case
Ideal for applications that require high availability with global read access.
Durability
Same as GRS (16 nines).
Geo-Zone-Redundant Storage (GZRS)
Description
Combines ZRS with GRS:
Data is synchronously replicated across three zones in the primary region.
Data is also asynchronously replicated to a secondary region.
Use Case
Best for critical applications requiring resiliency to both zonal and regional failures.
Durability
High durability with protection against zone and region outages.
Read-Access Geo-Zone-Redundant Storage (RA-GZRS)
Description
Extends GZRS by providing read-only access to data in the secondary region.
Use Case
Designed for applications needing zone and region redundancy with global read access.
Comparison Chart
| Replication Type | Number of Copies | Redundancy Scope | Secondary Region Access | Use Case |
|---|---|---|---|---|
| LRS | 3 | Single datacenter | No | Cost-efficient, local redundancy |
| ZRS | 3 | Multiple availability zones | No | High availability within a region |
| GRS | 6 | Region-level redundancy | No | Disaster recovery |
| RA-GRS | 6 | Region-level redundancy | Yes | Disaster recovery with global reads |
| GZRS | 6 | Zone + region redundancy | No | Resiliency to zone and region failures |
| RA-GZRS | 6 | Zone + region redundancy | Yes | Global read access with zone & region redundancy |
Key Factors to Consider
1. Durability
For critical data, prefer GRS, RA-GRS, GZRS, or RA-GZRS.
2. Availability Zones
Use ZRS for applications deployed in zones to ensure high availability.
3. Disaster Recovery
Choose GRS or GZRS to protect against regional failures.
4. Cost
LRS is the most cost-effective; RA-GZRS is the most expensive but offers the highest resilience.
Summary
By selecting the appropriate replication strategy, you can balance cost, performance, and data protection needs.
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