Azure: Set-AzVMOSDisk doesn't replace the OsDisk, but also doesn't show error

Question

Azure: Set-AzVMOSDisk doesn't replace the OsDisk, but also doesn't show error

Dan Black 26

I'm trying to restore a VM OsDisk back to a previously created Snapshot.

Here's my ps1 file:

Param($resourceGroupName, $vmName, $snapshotName)

$snapshot = Get-AzSnapshot -ResourceGroupName $resourceGroupName -SnapshotName $snapshotName 

$diskConfig = New-AzDiskConfig -Location $snapshot.Location -SourceResourceId $snapshot.Id -CreateOption Copy

$disk = New-AzDisk -Disk $diskConfig -ResourceGroupName $resourceGroupName -Name "$($vmName)_$([guid]::NewGuid())"

$vm = Get-AzVM -ResourceGroupName $resourceGroupName -Name $vmName

$oldDiskName = $vm.StorageProfile.OsDisk.Name

$virtualMachine = Set-AzVMOsDisk -VM $vm -ManagedDiskId $disk.Id -CreateOption Attach -Windows

Remove-AzDisk -ResourceGroupName $resourceGroupName -Name $oldDiskName -Force

The final step, to remove the old OsDisk, is throwing an error:

Disk <diskname> is attached to VM

Which means the old disk is still attached to the VM, which means that Set-AzVMOsDisk didn't work.

Any ideas?

Thanks

Ravi Kanth Koppala 3,391 Reputation points Microsoft Employee Moderator

2022-01-07T14:15:38.353+00:00

@Dan Black ,
Please do "Accept Answer" which might be beneficial to other community members reading this thread. Thanks

Accepted answer

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Ravi Kanth Koppala 3,391 Reputation points Microsoft Employee Moderator

2022-01-07T14:15:38.353+00:00

@Dan Black ,
Please do "Accept Answer" which might be beneficial to other community members reading this thread. Thanks

Answer 1

Hello @Dan Black ,
Glad that you are able to figure it out. Yes - That's the right approach.
By using Set-AzVMOSDisk you are modifying the state of the Virtual machine by using it's attributes and those changes are cached.
Now, in order for those changes to reflect - it needs to be followed by either Update-azVM / New-AzVM

Couple of examples:
https://learn.microsoft.com/en-us/powershell/module/az.compute/set-azvmdatadisk?view=azps-7.0.0

Other easy way of updating is: (You can just use pipe symbol followed by update-azvm)
Set-AzVMOSDisk -VM $azureVM -ManagedDiskId $newVMDisk.Id -Name $newVMDiskName | update-azvm

Answer 2

I got some help:

Set-AzVMOsDisk just stages the changes, but you then need to use Update-AzVM to apply the changes back to Azure like this:

Param(
    $resourceGroupName,
    $vmName,
    $snapshotName
)

# Get target VM and snapshot

$azureVM = Get-AzVM -ResourceGroupName $resourceGroupName -Name $vmName

$snapshot = Get-AzSnapshot -ResourceGroupName $resourceGroupName -SnapshotName $snapshotName



# Create new disk config and provision managed disk

$diskConfig = New-AzDiskConfig -Location $snapshot.Location -SourceResourceId $snapshot.Id -CreateOption 'Copy'

$oldVMDisk = $azureVM.StorageProfile.OsDisk.Name

$newVMDiskName = "$($vmName)_OsDisk_$([guid]::NewGuid())"

$newVMDisk = New-AzDisk -Disk $diskConfig -ResourceGroupName $resourceGroupName -Name $newVMDiskName 



# Set new OS managed disk (pending VM config)

Set-AzVMOSDisk -VM $azureVM -ManagedDiskId $newVMDisk.Id -Name $newVMDiskName 

# Apply pending VM config

Update-AzVM -ResourceGroupName $resourceGroupName -VM $azureVM

# Delete old OS disk

Remove-AzDisk -ResourceGroupName $resourceGroupName -Name $oldVMDisk -Force

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Azure: Set-AzVMOSDisk doesn't replace the OsDisk, but also doesn't show error

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