You are designing a disaster recovery (DR) solution from the North Europe region to the We… — Microsoft Azure Solutions Architect (AZ-305)

You are designing a disaster recovery (DR) solution from the North Europe region to the West Europe region for an e-commerce application hosted on Azure Virtual Machines. The application architecture and workload metrics are as follows:

* Web Tier: Two virtual machines, each with a single $128\text{ GB}$ Standard SSD OS disk. The average write churn is $0.2\text{ MB/s}$ per VM.
* Application Tier: Two virtual machines, each with a single $256\text{ GB}$ Premium SSD disk. The average write churn is $3\text{ MB/s}$ per VM.
* Database Tier: One SQL Server virtual machine with three Premium SSD disks: an OS disk ( $1.5\text{ MB/s}$ write churn), a data disk ( $12\text{ MB/s}$ write churn), and a transaction log disk ( $26\text{ MB/s}$ write churn).

The business continuity requirements specify:

* Web and Application Tiers: Recovery Point Objective (RPO) of $2\text{ hours}$ and Recovery Time Objective (RTO) of $2\text{ hours}$ .
* Database Tier: RPO of $15\text{ seconds}$ and RTO of $30\text{ minutes}$ .

Which two replication methods should you include in the disaster recovery design? (Select two.)

Replicate the Web and Application tier virtual machines to the target region using Azure Site Recovery.Answer
Replicate the database tier workload to the target region using SQL Server Always On Availability Groups.Answer
C
Replicate all virtual machines, including the database tier, to the target region using Azure Site Recovery with standard policy settings.
D
Replicate the database virtual machine to the target region using Azure Site Recovery with multi-VM consistency enabled.

Answer

Replicate the Web and Application tier virtual machines to the target region using Azure Site Recovery, and replicate the database tier workload to the target region using SQL Server Always On Availability Groups.

The correct design uses Azure Site Recovery for the Web and Application tiers because their write churn rates (

0.2\text{ MB/s}

and

3\text{ MB/s}

) are well within standard ASR limits (

10\text{ MB/s}

per disk) and their

2\text{ hours}

RPO requirement is easily satisfied. The database tier workload must be replicated using SQL Server Always On Availability Groups because the

15\text{ seconds}

RPO cannot be met by ASR's replication frequency, and SQL Server's native replication effectively handles the high

26\text{ MB/s}

log disk write churn.

Step-by-Step Solution

Analyze the RPO requirements for each application tier.

The Web and Application tiers require an RPO of

2\text{ hours}

, which is compatible with the replication frequencies of Azure Site Recovery. The Database tier requires a near-real-time RPO of

15\text{ seconds}

Azure Site Recovery (ASR) provides replication with recovery points typically generated every few minutes, which cannot satisfy a sub-minute (e.g.,

15\text{ seconds}

) RPO. Therefore, a database-native synchronous or low-latency asynchronous replication method is required for the database tier.

Evaluate the write churn limits for the database VM's disks against Azure Site Recovery limits.

The database transaction log disk write churn is

26\text{ MB/s}

. Under standard Azure Site Recovery policies, the write churn limit is

10\text{ MB/s}

per Premium SSD. ASR High Churn support can handle up to

20\text{ MB/s}

(standard high churn) or

30\text{ MB/s}

(highest churn) depending on VM sizing, but ASR still cannot meet the RPO requirement.

Validating write churn prevents replication lag, disk throttling, and failure to meet recovery objectives. The log disk's high churn of

26\text{ MB/s}

makes it a poor candidate for standard ASR replication.

Evaluate the write churn limits for the Web and Application VM disks.

The Web tier has

0.2\text{ MB/s}

churn, and the Application tier has

3\text{ MB/s}

churn. Both are well below the

10\text{ MB/s}

standard ASR limit.

This confirms that ASR is fully supported and cost-effective for replication of the Web and Application tiers.

Synthesize the final architecture.

Web and App tiers are replicated via Azure Site Recovery. The Database tier is replicated using SQL Server Always On Availability Groups to West Europe.

Combining Azure Site Recovery for stateless/low-churn application tiers with database-native replication for stateful/high-churn database tiers is the recommended Azure architecture to meet heterogeneous RPO/RTO and churn requirements.

Key Concept

Azure Site Recovery replication limits and using database-native replication for workloads with sub-minute RPO or high write churn.

Estimated Time:3m 0s

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Answer

Step-by-Step Solution

Key Concept

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