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Difficulty: MediumDesign Azure Site Recovery Solutions

An organization is designing a disaster recovery (DR) solution from the North Europe region to the West Europe region for an application hosted on an Azure Virtual Machine (VM1). The business requirements specify a Recovery Point Objective (RPO) of 15 minutes and a Recovery Time Objective (RTO) of 2 hours. VM1 runs a high-throughput PostgreSQL database and has the following disk configuration:

- OS Disk: 128 GB Premium SSD with a peak write churn of 2 MB/s
- Data Disk: 1 TB Premium SSD with a peak write churn of 28 MB/s
- Log Disk: 256 GB Premium SSD with a peak write churn of 32 MB/s

The total peak write churn for VM1 is 62 MB/s. Which disaster recovery design should you recommend to meet the requirements?

  1. Replicate VM1 using Azure Site Recovery, excluding the Data Disk and Log Disk from replication, and implement PostgreSQL native streaming replication to the target region for database data.Answer
  2. B
    Replicate VM1 and all of its disks using Azure Site Recovery, configuring the replication policy to use the High Churn tier.
  3. C
    Replicate VM1 and all of its disks using standard Azure Site Recovery replication.
  4. D
    Configure Azure Backup with Cross-Region Restore (CRR) to perform hourly backups of VM1 and restore them in the target region during a disaster.

Answer

Replicate VM1 using Azure Site Recovery, excluding the Data Disk and Log Disk from replication, and implement PostgreSQL native streaming replication to the target region for database data.
The correct design uses Azure Site Recovery to replicate the virtual machine's OS disk while excluding the high-churn database disks (Data Disk and Log Disk). To protect the database workload without exceeding replication thresholds, native database-level replication (PostgreSQL streaming replication) is implemented. This combination respects the per-disk limits of ASR (which caps Premium SSD write churn at 30 MB/s even with High Churn support) while ensuring database replication remains within the 15-minute RPO constraint.

Step-by-Step Solution

1
Analyze the write churn limits for standard Azure Site Recovery (ASR) replication.
Standard ASR limits write churn to 15 MB/s per Premium SSD disk and 54 MB/s per VM. The VM's Data Disk (28 MB/s), Log Disk (32 MB/s), and total VM churn (62 MB/s) all exceed these thresholds.
To determine if standard ASR replication is a viable option.
2
Analyze the write churn limits for ASR High Churn support.
ASR High Churn support allows up to 30 MB/s per Premium SSD disk and 100 MB/s per VM. While the total VM churn (62 MB/s) and Data Disk churn (28 MB/s) are within limits, the Log Disk peak write churn (32 MB/s) still exceeds the 30 MB/s per-disk limit.
To evaluate if the ASR High Churn feature can accommodate the workload.
3
Select a hybrid replication strategy combining ASR and native database replication.
Exclude the high-churn database disks (Data Disk and Log Disk) from ASR replication to avoid replication failures. Replicate the OS disk using ASR to handle VM configuration recovery, and set up native PostgreSQL streaming replication to replicate the database transactions with a low RPO/RTO.
To design a supported solution that meets the RPO and RTO requirements.

Key Concept

Azure Site Recovery (ASR) write churn limits and disk exclusion strategy
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Topics

Design Azure Site Recovery Solutions

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