Migrate to Managed Disks - Old OS / Agent Version

Question

Darren Hickman 0

We're planning on re-creating this VM, but as an immediate precaution we wanted to upgrade the disk to a managed one.

I wanted to confirm the possible options:

Creating a new "managed" copy of the disk and attaching it to the VM
1. Based on my research this will not work.
Using the "migrate to managed disks" functionality in the Azure GUI (or CLI).
1. My concern with this is the age of the OS / Agent version (based on mentions in the documentation linked above).
2. I wanted to confirm moving forward with this migration process is OK, or at the least that we'll be able to revert it / get the VM back to what it was (i.e. attaching the old non-managed disk and starting it) as we currently don't have the new instance set up.

Anonymous

2026-04-16T19:52:54.6933333+00:00
Darren Hickman - Creating a new managed disk copy and attaching it to the existing VM: Not supported for in-place OS disk replacement on a legacy, unmanaged‑disk VM. This approach is not recommended and will not work for safely converting the OS disk.

Using “Migrate to managed disks” (Portal/CLI): This is the correct and supported approach, even for older OS versions like Windows Server 2012. The migration is a metadata + platform operation and is not blocked by the OS or guest agent version (the VM must be deallocated during migration).

Revertability / rollback:

There is no automatic rollback after migration. Once migrated, the VM points to managed disks.

Best practice before migrating:

Take a snapshot/export of the unmanaged VHD(s) or

Create a backup copy of the VHDs in the storage account

This ensures you can manually recreate the VM using the old unmanaged disks if needed.

Proceed with Migrate to managed disks but take a snapshot/backup of the unmanaged disks first. This gives you a safety net until the new VM is ready.

Reference: https://learn.microsoft.com/en-us/azure/virtual-machines/windows/migrate-to-managed-disks
Anonymous

2026-04-17T23:50:00.02+00:00

Darren Hickman -Just checking if provided response was helpful! please let me know if you have any queries.

Your answer

Anonymous

2026-04-16T19:52:54.6933333+00:00

Darren Hickman - Creating a new managed disk copy and attaching it to the existing VM: Not supported for in-place OS disk replacement on a legacy, unmanaged‑disk VM. This approach is not recommended and will not work for safely converting the OS disk.

Using “Migrate to managed disks” (Portal/CLI): This is the correct and supported approach, even for older OS versions like Windows Server 2012. The migration is a metadata + platform operation and is not blocked by the OS or guest agent version (the VM must be deallocated during migration).

Revertability / rollback:

There is no automatic rollback after migration. Once migrated, the VM points to managed disks.

Best practice before migrating:

Take a snapshot/export of the unmanaged VHD(s) or

Create a backup copy of the VHDs in the storage account

This ensures you can manually recreate the VM using the old unmanaged disks if needed.

Proceed with Migrate to managed disks but take a snapshot/backup of the unmanaged disks first. This gives you a safety net until the new VM is ready.

Reference: https://learn.microsoft.com/en-us/azure/virtual-machines/windows/migrate-to-managed-disks
Anonymous

2026-04-17T23:50:00.02+00:00

Darren Hickman -Just checking if provided response was helpful! please let me know if you have any queries.