Azure Site Recovery learnings – Azure-To-Azure

A few things I’ve learned about Azure Site Recovery (ASR) recently, while doing an Azure-to-Azure DR design – some quite surprising:

  • Both your Recovery Services Vault AND it’s resource group must be located in a different region than the source
  • You need a cache storage account in the source region, however the staged incremental data will have negligible cost according to Microsoft
  • For source VMs utilizing Managed Disks, ASR will create destination Managed Disks and you will be charged for provisioned storage size, not consumed size. This differs from using unmanaged disks or for on-premises ASR, where consumed size is stored as page blobs in the destination storage account. I can’t find a Microsoft Doc link that specifically outlines this.
  • Egress bandwidth compression is estimated at about 60%, according to this blog post: Know exactly how much it will cost for enabling DR to your Azure VMs
  • VM Extensions are not replicated to a failover VM, and need to be manually installed: Doc Link
  • Secondary IP addresses are not replicated! These will need to be re-added through a Post-Failover task: Doc Link


Some things I still need to research and test are:

  • What happens if you perform a failover (or test failover) to a VM that is reporting into Log Analytics and Azure Automation (DSC, Update Management)? Will it seamlessly continue these operations, even when the VM extension no longer exists?
  • What happens to Azure Backup? Will the test failover VM using the Azure Backup Agent try to send backup data cross-region to the source Recovery Services Vault if the schedule time is triggered?

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