How to expand the OS drive of a Virtual Machine in an Azure Resource Group

10/18/2016
4 minutes to read
Contributors

Overview

When you create a new virtual machine (VM) in a Resource Group by deploying an image from Azure Marketplace, the default OS drive is often 127 GB (some images have smaller OS disk sizes by default). Even though it’s possible to add data disks to the VM (how many depending upon the SKU you’ve chosen) and moreover it’s recommended to install applications and CPU intensive workloads on these addendum disks, oftentimes customers need to expand the OS drive to support certain scenarios such as following:

Support legacy applications that install components on OS drive.
Migrate a physical PC or virtual machine from on-premises with a larger OS drive.

Important

Azure has two different deployment models for creating and working with resources: Resource Manager and Classic. This article covers using the Resource Manager model. Microsoft recommends that most new deployments use the Resource Manager model.

Warning

Resizing the OS Disk of an Azure Virtual Machine will cause it to restart.

Resize the OS drive

In this article we’ll accomplish the task of resizing the OS drive using resource manager modules of Azure Powershell. We will show resizing the OS drive for both Unmanaged and Managed disks since the approach to resize disks differs between both disk types.

For resizing Unmanaged Disks:

Open your Powershell ISE or Powershell window in administrative mode and follow the steps below:

Sign-in to your Microsoft Azure account in resource management mode and select your subscription as follows:
```
Connect-AzureRmAccount
Select-AzureRmSubscription –SubscriptionName 'my-subscription-name'
```

Set your resource group name and VM name as follows:

$rgName = 'my-resource-group-name'
$vmName = 'my-vm-name'

Obtain a reference to your VM as follows:

$vm = Get-AzureRmVM -ResourceGroupName $rgName -Name $vmName

Stop the VM before resizing the disk as follows:

Stop-AzureRmVM -ResourceGroupName $rgName -Name $vmName

And here comes the moment we’ve been waiting for! Set the size of the Unmanaged OS disk to the desired value and update the VM as follows:
```
$vm.StorageProfile.OSDisk.DiskSizeGB = 1023
Update-AzureRmVM -ResourceGroupName $rgName -VM $vm
```
Warning
The new size should be greater than the existing disk size. The maximum allowed is 2048 GB for OS disks. (It is possible to expand the VHD blob beyond that size, but the OS will only be able to work with the first 2048 GB of space.)
Updating the VM may take a few seconds. Once the command finishes executing, restart the VM as follows:
```
Start-AzureRmVM -ResourceGroupName $rgName -Name $vmName
```

For resizing Managed Disks:

Open your Powershell ISE or Powershell window in administrative mode and follow the steps below:

Sign-in to your Microsoft Azure account in resource management mode and select your subscription as follows:
```
Connect-AzureRmAccount
Select-AzureRmSubscription –SubscriptionName 'my-subscription-name'
```

Set your resource group name and VM name as follows:

$rgName = 'my-resource-group-name'
$vmName = 'my-vm-name'

Obtain a reference to your VM as follows:

$vm = Get-AzureRmVM -ResourceGroupName $rgName -Name $vmName

Stop the VM before resizing the disk as follows:

Stop-AzureRmVM -ResourceGroupName $rgName -Name $vmName

Obtain a reference to the Managed OS disk. Set the size of the Managed OS disk to the desired value and update the Disk as follows:
```
$disk= Get-AzureRmDisk -ResourceGroupName $rgName -DiskName $vm.StorageProfile.OsDisk.Name
$disk.DiskSizeGB = 1023
Update-AzureRmDisk -ResourceGroupName $rgName -Disk $disk -DiskName $disk.Name
```
Warning
The new size should be greater than the existing disk size. The maximum allowed is 2048 GB for OS disks. (It is possible to expand the VHD blob beyond that size, but the OS will only be able to work with the first 2048 GB of space.)
Updating the VM may take a few seconds. Once the command finishes executing, restart the VM as follows:
```
Start-AzureRmVM -ResourceGroupName $rgName -Name $vmName
```

And that’s it! Now RDP into the VM, open Computer Management (or Disk Management) and expand the drive using the newly allocated space.

Summary

In this article, we used Azure Resource Manager modules of Powershell to expand the OS drive of an IaaS virtual machine. Reproduced below is the complete script for your reference for both Unmanaged and Managed disks:

Unmanaged Disks:

Connect-AzureRmAccount
Select-AzureRmSubscription -SubscriptionName 'my-subscription-name'
$rgName = 'my-resource-group-name'
$vmName = 'my-vm-name'
$vm = Get-AzureRmVM -ResourceGroupName $rgName -Name $vmName
Stop-AzureRmVM -ResourceGroupName $rgName -Name $vmName
$vm.StorageProfile.OSDisk.DiskSizeGB = 1023
Update-AzureRmVM -ResourceGroupName $rgName -VM $vm
Start-AzureRmVM -ResourceGroupName $rgName -Name $vmName

Managed Disks:

Connect-AzureRmAccount
Select-AzureRmSubscription -SubscriptionName 'my-subscription-name'
$rgName = 'my-resource-group-name'
$vmName = 'my-vm-name'
$vm = Get-AzureRmVM -ResourceGroupName $rgName -Name $vmName
Stop-AzureRMVM -ResourceGroupName $rgName -Name $vmName
$disk= Get-AzureRmDisk -ResourceGroupName $rgName -DiskName $vm.StorageProfile.OsDisk.Name
$disk.DiskSizeGB = 1023
Update-AzureRmDisk -ResourceGroupName $rgName -Disk $disk -DiskName $disk.Name
Start-AzureRmVM -ResourceGroupName $rgName -Name $vmName

For resizing Data Disks

Though in this article, we focused primarily on expanding the Unmanaged/Managed OS disk of the VM, the developed script may also be used for expanding the data disks attached to the VM. For example, to expand the first data disk attached to the VM, replace the OSDisk object of StorageProfile with DataDisks array and use a numeric index to obtain a reference to first attached data disk, as shown below:

Unmanaged Disk:

$vm.StorageProfile.DataDisks[0].DiskSizeGB = 1023

Managed Disk:

$disk= Get-AzureRmDisk -ResourceGroupName $rgName -DiskName $vm.StorageProfile.DataDisks[0].Name
$disk.DiskSizeGB = 1023

Similarly you may reference other data disks attached to the VM, either by using an index as shown above or the Name property of the disk as illustrated below: