Azure Site Recovery now supports churn (data change rate) up to 100 MB/s per VM. You will be able to protect your Azure VMs having high churning workloads (like databases) using Azure Site Recovery which earlier could not be protected efficiently because Azure Site Recovery has churn limits up to 54 MB/s per VM. You may be able to achieve better RPO performance for your high churning workloads.

Table of contents:

Limitations

  • Available only for DR of Azure VMs.
  • Recommend VM SKUs with RAM of min 32GB.
  • Source disks must be Managed Disks.
Warning:
Azure Site Recovery recommends using High Churn while using following regions only as the Source region or the Target region: Japan East, Japan West, UK South, UK West, West US, West US 2, East Asia, East US, East US 2, Australia East, Australia Southeast, Canada East, Canada Central, Central US, West India and Southeast Asia. When using High Churn with any other regions outside the regions in the list, replication and/or reprotection may fail.

Data change limits

  • These limits are based on our tests and don’t cover all possible application I/O combinations.
  • Actual results may vary based on your app I/O mix.
  • There are two limits to consider, per disk data churn and per virtual machine data churn.
  • Limit per virtual machine data churn – 100 MB/s.

The following table summarizes Site Recovery limits:

Target Disk TypeAvg I/O SizeAvg Churn Supported
Standard or P10 or P158 KB2 MB/s
Standard or P10 or P1516 KB4 MB/s
Standard or P10 or P1524 KB6 MB/s
Standard or P10 or P1532 KB and above10 MB/s
P208 KB10 MB/s
P2016 KB20 MB/s
P2024 KB and above30 MB/s
P30 and above8 KB20 MB/s
P30 and above16 KB35 MB/s
P30 and above24 KB and above50 MB/s

How to enable High Churn support

From Recovery Service Vault

  1. Select source VMs on which you want to enable replication. To enable replication, follow the steps here.
  2. Under Replication Settings > Storage, select View/edit storage configuration. The Customize target settings page opens.Screenshot of Replication settings storage.
  3. Under Churn for the VM, there are two options:
    • Normal Churn (default option) – You can get up to 54 MB/s per VM. Select Normal Churn to use Standard storage accounts only for Cache Storage. Hence, Cache storage dropdown will list only Standard storage accounts.
    • High Churn – You can get up to 100 MB/s per VM. Select High Churn to use Premium Block Blob storage accounts only for Cache Storage. Hence, Cache storage dropdown will list only Premium Block blob storage accounts.Screenshot of churn.
  4. Select High Churn (Public Preview).Screenshot of high-churn.If you select multiple source VMs to configure Site Recovery and want to enable High Churn for all these VMs, select High Churn at the top level.Screenshot of churn top level.
  5. After you select High Churn for the VM, you will see Premium Block Blob options only available for cache storage account. Select cache storage account and then select Confirm Selection.Screenshot of Cache storage.
  6. Configure other settings and enable the replication.

From Azure VM screen

  1. In the portal, go to Virtual machines and select the VM.
  2. On the left pane, under Operations, select Disaster recovery.Screenshot of Disaster recovery page.
  3. Under Basics, select the Target region and then select Next: Advanced settings.
  4. Under Advanced settings, select Subscription, VM resource group, Virtual network, Availability, and Proximity placement group as required.
  5. Under Advanced settings > Storage settings, select [+] Show details.Screenshot of Storage show details.
  6. Under Storage settings > Churn for the VM, select High Churn (Public Preview). You will be able to use Premium Block Blob type of storage accounts only for cache storage.Screenshot of Churn for VM.
  7. Select Next: Review + Start replication.
Note:
* You can only enable High Churn only when you enable replication while configuring Azure Site Recovery on a VM.
* If you want to enable High Churn support for VMs already protected by Azure Site Recovery, disable replication for those VMs and select High Churn while enabling replication again. Similarly, disable and enable replication again to switch back to Normal Churn.

Cost Implications:

  • High Churn uses Premium Block Blob storage accounts which may have higher cost implications as compared to Normal Churn which uses Standard storage accounts. For more information, see pricing.
  • For High churn VMs, more data changes may get replicated to target for High churn compared to Normal churn. This may lead to more network cost.
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