An agricultural technology company hosts an IoT crop telemetry application on Azure virtua… — Microsoft Azure Solutions Architect (AZ-305)

An agricultural technology company hosts an IoT crop telemetry application on Azure virtual machines in the West US 2 region. The application architecture consists of:

- `vm-app01`: An application tier virtual machine with a total write churn of $4\text{ MB/s}$ on a single disk.
- `vm-db01`: A SQL Server database tier virtual machine with a database data disk experiencing a write churn of $12\text{ MB/s}$ and a transaction log disk experiencing a continuous write churn of $32\text{ MB/s}$ .

You need to design a disaster recovery (DR) solution to the East US region that meets the following requirements:
- A Recovery Time Objective (RTO) of $1\text{ hour}$ for the entire application.
- A Recovery Point Objective (RPO) of less than $10\text{ seconds}$ for the database tier.
- Minimize replication costs and administrative complexity.

Which disaster recovery strategy should you recommend?

A
Replicate both `vm-app01` and `vm-db01` to the East US region using Azure Site Recovery with standard replication policies.
B
Replicate all virtual machine disks to the East US region using Read-Access Geo-Redundant Storage (RA-GRS) and manually attach them to newly provisioned virtual machines during a disaster.
Replicate `vm-app01` using Azure Site Recovery. Configure SQL Server Always On Availability Groups to replicate the database to a SQL Server instance running on a virtual machine in the East US region.Answer
D
Configure Azure Backup with cross-region restore (CRR) to perform hourly backups of both virtual machines to a vault in the East US region.

Answer

Replicating the application virtual machine using Azure Site Recovery and configuring SQL Server Always On Availability Groups to replicate the database to a virtual machine in the target region.

The correct strategy is to replicate the application VM using Azure Site Recovery and configure SQL Server Always On Availability Groups for the database VM. The application VM's write churn of

4\text{ MB/s}

is well within Azure Site Recovery's limits. However, the database VM has a transaction log disk with

32\text{ MB/s}

of write churn, which exceeds the standard Azure Site Recovery limit of

10\text{ MB/s}

per disk. Moreover, Azure Site Recovery replicates asynchronously with crash-consistent recovery points typically in minutes, which cannot satisfy the strict database Recovery Point Objective (RPO) of less than

10\text{ seconds}

. SQL Server Always On Availability Groups in asynchronous-commit mode provides near-real-time replication that can easily achieve the sub-10-second RPO while bypassing the disk-level write churn limitations of Azure Site Recovery.

Step-by-Step Solution

Analyze the RPO and write churn metrics for the database tier to determine suitability for Azure Site Recovery.

The database VM has a transaction log disk with a write churn of

32\text{ MB/s}

, which exceeds the standard Azure Site Recovery limit of

10\text{ MB/s}

per disk. In addition, the required RPO is less than

10\text{ seconds}

, which is lower than the typical RPO of Azure Site Recovery (minutes).

Identifying these constraints prevents replication failures and ensures that the disaster recovery design meets the system's performance and data loss requirements.

Determine the appropriate replication method for the database VM.

Native SQL Server replication, such as SQL Server Always On Availability Groups in asynchronous-commit mode, is selected for the database VM.

SQL Server Always On Availability Groups bypasses Azure Site Recovery storage-level churn limits and provides near-real-time asynchronous replication capable of meeting the sub-10-second RPO.

Determine the replication method for the application VM (vm-app01).

Azure Site Recovery is selected to replicate the application VM to the target region.

The application VM's write churn of

4\text{ MB/s}

is well within standard Azure Site Recovery limits, and Azure Site Recovery easily meets the

1\text{ hour}

Recovery Time Objective (RTO) for the application tier.

Key Concept

Azure Site Recovery disk-level write churn limits and selection of native database replication for low-RPO workloads.

Estimated Time:2m 0s

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