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Protecting large data disks using Azure Site Recovery

Azure Site Recovery users cannot directly protect Hyper-V VMs that have a data disk (VHD) with size greater than 1 TB. This blog describes a workaround that helps you protect Hyper-V VMs with data disks larger than 1 TB.

Azure Site Recovery users cannot directly protect Hyper-V VMs that have any data disk (VHD) with size greater than 1 TB. This is due to an Azure limitation of 1 TB data disk size limit for IaaS VMs (at the time of publishing this blog). This blog describes a workaround which involves the creation of a new striped volume made up of multiple smaller VHDs, each of which is less than 1TB. Once the data is migrated to the new disk drive and the old large VHD is removed from the Hyper-V virtual machine, Azure Site Recovery can be used to protect the VM.

The following instructions are applicable for VMs running Windows, and have been tested with Windows Server 2012 R2. You can follow a similar procedure for Linux VMs using RAID.

  • Add multiple 1000 GB VHD’s to the VM. The number of VHDs depends on the size of the old VHD in TB – example, to replace a 3.2 TB VHD, you would need to create 4 VHD’s of 1000 GB each.
  • Turn off the applications running inside the VM (for example, SQL server etc.)
  • Open Computer Management. Go to the Disk management tab. If prompted to initialize the new disks, click OK.
  • Right click on one of the new Unallocated volumes and click on “Create Striped volume
  • Select all the unallocated disks in the wizard to create a striped volume out of the newly added VHD’s

New striped volume

  • Assign a temporary drive letter (say E:) to the new drive. Select the appropriate file system and select Quick format option.
  • Copy data from old drive to the new drive using the command: robocopy D: E: /mir. Assuming D: is the volume where the data currently resides.
  • Then use the Change Drive Letter and Paths wizard of the Disk management console to do the following
    • Remove the old drive’s letter (D:)
    • Remove the temporary drive letter from the new drive (E:)
    • Assign D: to the new drive
  • Use Powershell to run diskpart. Type “SAN POLICY=OnlineAll
  • Shutdown the VM
  • Remove the old VHD from the VM using Hyper-V Manager
  • Start the VM, application services and validate the availability of your application/server
  • Enable protection for your VM using Azure Site Recovery


So, what are you waiting for? Start protecting your Hyper-V virtual machines (large or small) to Azure with Azure Site Recovery.

If you are new to Azure, you can sign-up for a free Azure trial to get started with Azure Site Recovery.