Performing Guest OS Customization Automatically During VM Conversion

When converting a VM from any other hypervisor to Azure, guest OS customization is performed and the transport mode is changed to direct upload to managed disk (DUMD) automatically.

With DUMD, empty managed disks are first created in Azure. The VM disk data is then written directly into these disks through the upload stream. Once the upload finishes and the disk is sealed, a VM is created out of the managed disks.

Requirements

Windows Source VMs

• Configure your host firewall (Windows firewall or similar) to allow access to Remote Desktop Protocol (RDP) and Network discovery. Otherwise, you cannot access your Azure VM after the conversion is complete.

• Enable RDP.

Linux Source VMs

• Enable Secure Shell (SSH) for remote access.

• The host firewall (such as Linux iptables) must permit access to SSH.

• Verify that Linux VMs use GRUB (GRUB legacy) or GRUB 2 as the bootloader.

• Linux VMs must use one of the following for the root file system: ext2, ext3, ext4, Btrfs, JFS, or XFS.

• Linux VM /etc/fstab entries should use UUIDs instead of device names, because device names might change during replication. For information about updating fstab entries to use UUIDs, see Updating fstab Entries to Use UUIDs. Disk Space Requirements

• Ensure that at least 2 GB of free space is available on the C: drive (for Windows) or on the root (/) directory (for Linux).

Supported Operating Systems

Linux - BIOS and UEFI

• RHEL Family: Red Hat Enterprise Linux (RHEL), Rocky Linux, Oracle Linux, CentOS

• Debian Family: Ubuntu, Debian

• SUSE: SUSE Linux Enterprise Server (SLES), openSUSE

Windows - BIOS and UEFI

• Microsoft Windows Server 2016 (Standard, Datacenter) (64-bit only)

• Microsoft Windows Server 2019 (Standard, Datacenter) (64-bit only)

• Microsoft Windows Server 2022 (Standard, Datacenter) (64-bit only)

• Microsoft Windows Server 2025 (Standard, Datacenter) (64-bit only)

• Microsoft Windows Server 2025 with legal notice (Standard, Datacenter) (64-bit only)

Supported Volume and File System Types (Azure)

The MBR and GPT formatted Azure Managed Disks are supported for both OS and data disks for Windows and Linux operating systems.

Windows

• Azure Virtual Machines with Managed Disks that use Master Boot Record (MBR) and GUID Partition Table (GPT) partitioning are supported.

Linux

• You can convert Linux VMs that use one of the following for the root file system: ext2, ext3, ext4, Btrfs, JFS, or XFS.

Direct Upload to Managed Disk Write Process

1. Create an empty managed disk in the target subscription, resource group, and region using the Microsoft.Compute/disks/write API (with createOption=Upload).

2. Obtain a write-access SAS URI for the disk upload by calling the beginGetAccess API (Microsoft.Compute/disks/beginGetAccess) with access=Write.

3. Upload backup data retrieved from the storage library directly to the managed disk using Put Page operations of the Azure Storage API.

4. Once the managed disks are restored, create a customizer node from image. The customizer node is named “cvcustomizernode” and will be created in the same subscription, region, and zone as the restore VM.

5. Attach the restored managed OS disk to the customizer node and wait for 3-5 minutes for the customization to complete.

   For more information on customization, see Injecting Drivers Automatically Using Direct Upload to Managed Disk Conversion.

6. Detach the disk from the customizer node.

7. Delete the customizer node and its resources.

8. Deploy an Azure VM from the managed disks.

Related Topics

• For information about how to automatically install drivers, Injecting Drivers Automatically Using Direct Upload to Managed Disk Conversion.

• For troubleshooting and installing drivers manually, see Troubleshooting for Converting to Azure Resource Manager