An enterprise is designing a disaster recovery (DR) solution from the East US region to th… — Microsoft Azure Solutions Architect (AZ-305)

An enterprise is designing a disaster recovery (DR) solution from the East US region to the West US region for a critical retail application. The source environment consists of the following Azure Virtual Machines:
- `web-vm1`: A web server VM with $2$ Premium SSD v1 disks. Each disk has a write churn rate of $4\text{ MB/s}$ , resulting in a total VM write churn of $8\text{ MB/s}$ .
- `db-vm1`: A database server VM running SQL Server on Azure VMs. It has $3$ Premium SSD v1 disks: one OS disk with a write churn of $2\text{ MB/s}$ , one database data disk with a write churn of $12\text{ MB/s}$ , and one transaction log disk with a write churn of $28\text{ MB/s}$ .

The DR design must meet the following business continuity requirements:
- The web server must achieve a Recovery Point Objective (RPO) of under $4\text{ hours}$ and a Recovery Time Objective (RTO) of under $2\text{ hours}$ .
- The database server must achieve an RPO of under $10\text{ seconds}$ and an RTO of under $15\text{ minutes}$ during a regional outage.

Which recovery design should you recommend to meet these requirements?

Replicate `web-vm1` using Azure Site Recovery. For `db-vm1`, deploy a secondary SQL Server virtual machine in the West US region and configure SQL Server Always On Availability Groups with asynchronous commit replication.Answer
B
Replicate both `web-vm1` and `db-vm1` using Azure Site Recovery, configuring the high-churn replication tier for all disks associated with the database virtual machine.
C
Replicate `web-vm1` using Azure Site Recovery. For `db-vm1`, migrate the database to Azure SQL Database and configure active geo-replication to provide automatic failover and a single read-write listener endpoint.
D
Replicate both `web-vm1` and `db-vm1` using Azure Site Recovery, and route incoming user traffic using Azure Traffic Manager configured to perform SSL offloading and path-based routing.

Answer

The correct design is to replicate the web server using Azure Site Recovery and to configure SQL Server Always On Availability Groups with asynchronous commit replication for the database server.

The web server's write churn (

4\text{ MB/s}

per disk,

8\text{ MB/s}

total) is well within the standard limits of Azure Site Recovery, making it suitable for VM-level replication. However, the database server's transaction log disk has a write churn of

28\text{ MB/s}

, which exceeds the

20\text{ MB/s}

per-disk limit of the Azure Site Recovery high-churn replication tier. Therefore, database-level replication using SQL Server Always On Availability Groups with asynchronous commit must be designed to handle the database write churn and meet the low RPO requirement of under

10\text{ seconds}

Step-by-Step Solution

Evaluate the write churn requirements for the VM disks against Azure Site Recovery limits.

The web server disks (

4\text{ MB/s}

each,

8\text{ MB/s}

total) are within the standard

10\text{ MB/s}

ASR disk limit. The database server's transaction log disk has a churn of

28\text{ MB/s}

, which exceeds the high-churn tier limit of

20\text{ MB/s}

per disk.

To determine if Azure Site Recovery can support the VM workload replication natively.

Identify alternative replication mechanisms for the database workload.

SQL Server Always On Availability Groups with asynchronous commit replication allows near-real-time data replication at the database level without being limited by block-level storage replication thresholds.

To satisfy the low RPO (

< 10\text{ seconds}

) requirement of the database tier despite the high write churn.

Assess the routing and database deployment constraints.

Active geo-replication does not support automatic failover with a single read-write listener endpoint, and Azure Traffic Manager cannot perform SSL offloading or path-based routing because it operates strictly at the DNS level.

To eliminate invalid architectural options that violate traffic management or database capabilities.

Key Concept

Azure Site Recovery write churn limits and database-level replication options for cross-region disaster recovery

Question

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Key Concept

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