A media streaming company hosting its application in the Azure North Europe region wants t… — Microsoft Azure Solutions Architect (AZ-305)

A media streaming company hosting its application in the Azure North Europe region wants to design a disaster recovery (DR) solution to the West Europe region. The application runs on two Azure virtual machines (VMs):

- `vm-web`: A web server VM with one Standard SSD disk that has a write churn rate of $3\text{ MB/s}$ .
- `vm-db`: A SQL Server database VM with two Premium SSD disks: a data disk with a write churn rate of $12\text{ MB/s}$ and a log disk with a write churn rate of $25\text{ MB/s}$ .

The disaster recovery solution must achieve a Recovery Point Objective (RPO) of 2 hours and a Recovery Time Objective (RTO) of 4 hours.

Which disaster recovery configuration should you recommend to meet these requirements?

Replicate `vm-web` using Azure Site Recovery, and configure SQL Server Always On Availability Groups to replicate the databases on `vm-db` to the West Europe region.Answer
B
Replicate both `vm-web` and `vm-db` to the West Europe region using Azure Site Recovery with enhanced replication and high-churn support enabled.
C
Replicate both `vm-web` and `vm-db` to the West Europe region using Azure Site Recovery with standard replication.
D
Configure Read-Access Geo-Redundant Storage (RA-GRS) for the managed disks of both `vm-web` and `vm-db` to enable geo-replication, and boot the VMs in West Europe during a failover.

Answer

Replicate `vm-web` using Azure Site Recovery, and configure SQL Server Always On Availability Groups to replicate the databases on `vm-db` to the West Europe region.

The correct configuration is to replicate the web server VM using Azure Site Recovery and to configure SQL Server Always On Availability Groups to replicate the database. This is because the database log disk write churn of

25\text{ MB/s}

exceeds the maximum supported write churn limit of

20\text{ MB/s}

per Premium SSD disk for Azure Site Recovery (even with enhanced high-churn support). Therefore, native SQL Server replication must be utilized for the database tier, while the web tier can be safely replicated using ASR since its disk churn of

3\text{ MB/s}

is well within limits.

Step-by-Step Solution

Analyze the write churn rates of each disk in the source environment.

The web VM has a single disk with

3\text{ MB/s}

churn. The database VM has one disk with

12\text{ MB/s}

churn and another with

25\text{ MB/s}

churn.

Understanding the individual disk throughput requirements is necessary to verify compliance with Azure Site Recovery limits.

Compare disk churn rates against Azure Site Recovery (ASR) limits.

The web VM disk fits within standard and enhanced limits. However, the database log disk (

25\text{ MB/s}

) exceeds both the standard (

10\text{ MB/s}

) and enhanced/high-churn (

20\text{ MB/s}

) per-disk write churn limits of ASR.

Exceeding these limits causes replication lag, RPO violations, and replication health degradation.

Select alternative replication mechanisms for workloads exceeding ASR limits.

Use SQL Server Always On Availability Groups for the database tier to replicate data asynchronously to the target region, satisfying the 2-hour RPO. Use ASR for the web tier VM since its churn rate is well within supported limits.

This hybrid design ensures that database transaction logs are replicated natively without being blocked by ASR disk churn limits, while the web tier VM is replicated using ASR.

Key Concept

Azure Site Recovery limits require separating high-churn database workloads to native replication tools like SQL Server Always On Availability Groups when disk write churn exceeds supported limits.

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