17 Oct

Retrieve the size of the OS Disk in Resource Manager Azure Deployments using PowerShell

Recently I noticed that a script I was using wasn’t quite working correctly because it was failing to get the size of a Azure VM’s disk.

Usually I would use something similar to the following:

$VM = Get-AzureRmVM -ResourceGroupName $ResourceGroupName -Name $VirtualMachineName
$size = $VM.StorageProfile.OsDisk.DiskSizeGB

However $VM.StorageProfile.OsDisk.DiskSizeGB was null. I decided that I would write a function instead which would go and look at the underlying vhd blob and find the size that way. The below is my code and usage:

function Get-AzureRmVhdSize {

        [Uri] $uri = $(throw "Please enter a URI")
    $blobEndpoint = $uri.Scheme + "://" + $uri.Host + "/"
    $sa = Get-AzureRmStorageAccount | ? { $_.PrimaryEndpoints.Blob -eq $blobEndpoint }

    if ($sa -eq $null -or $sa.Length -ne 1) {

        Throw "Unable to locate storage account"


    $containerAndBlob = $uri.AbsolutePath.Split("/", [StringSplitOptions]::RemoveEmptyEntries)

    $blob = Get-AzureStorageBlob -Blob $containerAndBlob[1] -Container $containerAndBlob[0] -Context $sa.Context

    $sizeInBytes = $blob.Length
    $sizeInGB = [int]($sizeInBytes/1073741824)

    return $sizeInGB


function Get-AzureRmOSDiskSize {

        [string]$VirtualMachineName = $(throw "Specify virtual machine name"),
        [string]$ResourceGroupName = $(throw "Specify resource group name")

    $VM = Get-AzureRmVM -ResourceGroupName $ResourceGroupName -Name $VirtualMachineName

    if ($VM -eq $null) {

        throw "Virtual Machine Not Found"


    return Get-AzureRmVhdSize -uri $VM.StorageProfile.OsDisk.Vhd.Uri


Get-AzureRmOSDiskSize -VirtualMachineName testvm -ResourceGroupName testrg