Powershell script to reduce OS disk size in Azure is safe to run?

Question

Powershell script to reduce OS disk size in Azure is safe to run?

TechGuy_MS1 61

Hi... I am new at Azure and not familiar with PowerShell scripts. I found following method to reduce the OS disk size via script. I want to know is it safe and secure to run this script? Since the script seems granting some permissions (with admin rights), any possible security, data theft/lost etc or any other issues? I just want to make sure script is COMPLETELY safe and secure to run.

Looking for kind feedback please.

https://jrudlin.github.io/2019-08-27-shrink-azure-vm-osdisk/
https://github.com/jrudlin/Azure/blob/master/General/Shrink-AzDisk.ps1

Thanks.

Answer accepted by question author

2 additional answers

Your answer

Answer 1

Andreas Baumgarten 129.4K MVP Volunteer Moderator

Hi @TechGuy_MS1 ,

The script is pretty straight forward and is not doing something suspicious.
After everything is done and the VM is up and running again without any issues I would recommend to check if the temporary created storage account still exists (not deleted). If the temporary created storage account still exist just delete this.

----------

(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)

Regards
Andreas Baumgarten

TechGuy_MS1 61 Reputation points

2021-02-19T15:05:53.207+00:00

Excellent!
Thanks for the info.

Answer 2

Hello @TechGuy_MS1 ,

Thanks for reaching out

I have reviewed and executed each line from this script individually and didn't find anything suspicious or problematic from security standpoint except below error which caused due to Az/ Azure RM modules were coexist on my system and when I updated Az module after removing Azure RM module which started working as expected without any issue.

Error: Update-AzVM : Required parameter 'bootDiagnostics.storageAccountUri' is missing (null).
Resolution: Uninstall the AzureRM and install Az module

I had tested this one on my azure VM, was able to Shrink Az disk. Here, I am attaching PS success outcome for your reference.

I hope this help you, If you have any additional queries, feel free to reach out to us, I would be happy to help you out. Thanks.

PowerShell Outcome:

PS C:\> # Variables  
$DiskID = "/subscriptions/xxxxx-xxx-xxxx-xxxx-xxxxxxfff/resourceGroups/CXP/providers/Microsoft.Compute/disks/testvm_OsDisk_1_93481399ceeb487e8ab46c4830ccc036"# eg. "/subscriptions/xxxxx-xxx-xxxx-xxxx-xxxxxxfff/resourcegroups/rg-server1-prod-1/providers/Microsoft.Compute/disks/Server1-Server1"  
$VMName = "testvm"  
$DiskSizeGB = 32  
$AzSubscription = "Microsoft Azure Internal Consumption"  
  
PS C:\> Connect-AzAccount  
  
Account                    SubscriptionName                     TenantId                             Environment  
-------                    ----------------                     --------                             -----------  
******@xxxxx.onmicrosoft.com Microsoft Test Sub xxxxx-xxx-xxxx-xxxx-xxxxxxfff        AzureCloud   
  
  
PS C:\> Select-AzSubscription -Subscription $AzSubscription  
PS C:\> $VM = Get-AzVm | ? Name -eq $VMName  
PS C:\> $VM = Get-AzVm | ? Name -eq $VMName  
PS C:\> $resourceGroupName = $VM.ResourceGroupName  
PS C:\> $Disk = Get-AzDisk | ? Id -eq $DiskID  
PS C:\> $HyperVGen = $Disk.HyperVGeneration  
PS C:\> $DiskName = $Disk.Name  
PS C:\> $SAS = Grant-AzDiskAccess -ResourceGroupName $resourceGroupName -DiskName $DiskName -Access 'Read' -DurationInSecond 600000;  
PS C:\> $storageAccountName = "shrink" + [system.guid]::NewGuid().tostring().replace('-','').substring(1,18)  
PS C:\> $storageContainerName = $storageAccountName  
PS C:\> $destinationVHDFileName = "$($VM.StorageProfile.OsDisk.Name).vhd"  
PS C:\> $StorageAccount = New-AzStorageAccount -ResourceGroupName $resourceGroupName -Name $storageAccountName -SkuName Standard_LRS -Location $VM.Location  
PS C:\> $destinationContext = $StorageAccount.Context  
PS C:\> $container = New-AzStorageContainer -Name $storageContainerName -Permission Off -Context $destinationContext  
  
PS C:\> Start-AzStorageBlobCopy -AbsoluteUri $SAS.AccessSAS -DestContainer $storageContainerName -DestBlob $destinationVHDFileName -DestContext $destinationContext  
while(($state = Get-AzStorageBlobCopyState -Context $destinationContext -Blob $destinationVHDFileName -Container $storageContainerName).Status -ne "Success") { $state; Start-Sleep -Seconds 20 }  
$state  
  
PS C:\> Revoke-AzDiskAccess -ResourceGroupName $resourceGroupName -DiskName $DiskName  
  
PS C:\> $destinationVHDFileName = "$($VM.StorageProfile.OsDisk.Name).vhd"  
  
PS C:\> $destinationVHDFileName  
testvm_OsDisk_1_93481399ceeb487e8ab46c4830ccc036.vhd  
  
PS C:\> $emptydiskforfootername = "$($VM.StorageProfile.OsDisk.Name)-empty.vhd"  
  
  
PS C:\> $diskConfig = New-AzDiskConfig `  
    -Location $VM.Location `  
    -CreateOption Empty `  
    -DiskSizeGB $DiskSizeGB `  
    -HyperVGeneration $HyperVGen  
  
PS C:\> $dataDisk = New-AzDisk `  
    -ResourceGroupName $resourceGroupName `  
    -DiskName $emptydiskforfootername `  
    -Disk $diskConfig  
  
PS C:\> $VM = Add-AzVMDataDisk `  
    -VM $VM `  
    -Name $emptydiskforfootername `  
    -CreateOption Attach `  
    -ManagedDiskId $dataDisk.Id `  
    -Lun 63  
  
PS C:\> Update-AzVM -ResourceGroupName $resourceGroupName -VM $VM  
  
  
RequestId IsSuccessStatusCode StatusCode ReasonPhrase  
--------- ------------------- ---------- ------------  
                         True         OK OK            
  
PS C:\> $VM | Stop-AzVM -Force  
OperationId : 499dc01f-b5ce-4753-b1cc-5f06bfe1109c  
Status      : Succeeded  
StartTime   : 24-Feb-21 5:39:56 PM  
EndTime     : 24-Feb-21 5:40:08 PM  
Error       :   
  
PS C:\> $SAS = Grant-AzDiskAccess -ResourceGroupName $resourceGroupName -DiskName $emptydiskforfootername -Access 'Read' -DurationInSecond 600000;  
  
PS C:\> Start-AzStorageBlobCopy -AbsoluteUri $SAS.AccessSAS -DestContainer $storageContainerName -DestBlob $emptydiskforfootername -DestContext $destinationContext  
while(($state = Get-AzStorageBlobCopyState -Context $destinationContext -Blob $emptydiskforfootername -Container $storageContainerName).Status -ne "Success") { $state; Start-Sleep -Seconds 20 }  
$state  
  
   AccountName: shrinkc95365ba3f7498991f, ContainerName: shrinkc95365ba3f7498991f  
  
  
CopyId                  : c0864f4c-8475-487e-802d-2f89a8b06af4  
CompletionTime          : 24-Feb-21 12:26:27 PM +00:00  
Status                  : Success  
Source                  : https://md-mvj44jsj*********************  
BytesCopied             : 34359738880  
TotalBytes              : 34359738880  
StatusDescription       :   
DestinationSnapshotTime :   
  
PS C:\> Revoke-AzDiskAccess -ResourceGroupName $resourceGroupName -DiskName $emptydiskforfootername  
  
Name      : d3a96c26-189a-4246-aca4-2b8bb0b2ff5c  
StartTime : 24-Feb-21 5:57:24 PM  
EndTime   : 24-Feb-21 5:57:55 PM  
Status    : Succeeded  
Error     :   
  
PS C:\> Remove-AzVMDataDisk -VM $VM -DataDiskNames $emptydiskforfootername  
  
ResourceGroupName   Name   Location       VmSize  OsType       NIC ProvisioningState Zone  
-----------------   ----   --------       ------  ------       --- ----------------- ----  
CXP               testvm westeurope Standard_B1s Windows testvm761         Succeeded       
  
  
PS C:\> Update-AzVM -ResourceGroupName $resourceGroupName -VM $VM  
  
RequestId IsSuccessStatusCode StatusCode ReasonPhrase  
--------- ------------------- ---------- ------------  
                         True         OK OK            
  
PS C:\> Remove-AzDisk -ResourceGroupName $resourceGroupName -DiskName $emptydiskforfootername -Force;  
  
Name      : d547bbc4-a1f4-45cf-a9e7-ca3452865baf  
StartTime : 24-Feb-21 6:02:16 PM  
EndTime   : 24-Feb-21 6:02:47 PM  
Status    : Succeeded  
Error     :   
  
PS C:\> $emptydiskforfootername  
testvm_OsDisk_1_93481399ceeb487e8ab46c4830ccc036-empty.vhd  
  
PS C:\> $emptyDiskblob = Get-AzStorageBlob -Context $destinationContext -Container $storageContainerName -Blob $emptydiskforfootername  
PS C:\> $emptyDiskblob  
  
   AccountName: shrinkc95365ba3f7498991f, ContainerName: shrinkc95365ba3f7498991f  
  
Name                 BlobType  Length          ContentType                    LastModified         AccessTier SnapshotTime                 IsDeleted  VersionId                       
----                 --------  ------          -----------                    ------------         ---------- ------------                 ---------  ---------                       
testvm_OsDisk_1_9... PageBlob  34359738880     application/octet-stream       2021-02-24 12:26:27Z Unknown                                 False                                      
  
PS C:\> $osdisk = Get-AzStorageBlob -Context $destinationContext -Container $storageContainerName -Blob $destinationVHDFileName  
  
PS C:\> $osdisk  
  
   AccountName: shrinkc95365ba3f7498991f, ContainerName: shrinkc95365ba3f7498991f  
  
Name                 BlobType  Length          ContentType                    LastModified         AccessTier SnapshotTime                 IsDeleted  VersionId                       
----                 --------  ------          -----------                    ------------         ---------- ------------                 ---------  ---------                       
testvm_OsDisk_1_9... PageBlob  136367309312    application/octet-stream       2021-02-24 10:37:51Z Unknown                                 False                                      
  
  
PS C:\> $footer = New-Object -TypeName byte[] -ArgumentList 512  
  
PS C:\> write-output "Get footer of empty disk"  
Get footer of empty disk  
  
PS C:\> $downloaded = $emptyDiskblob.ICloudBlob.DownloadRangeToByteArray($footer, 0, $emptyDiskblob.Length - 512, 512)  
  
PS C:\> $osDisk.ICloudBlob.Resize($emptyDiskblob.Length)  
  
PS C:\> $footerStream = New-Object -TypeName System.IO.MemoryStream -ArgumentList (,$footer)  
  
PS C:\> write-output "Write footer of empty disk to OSDisk"  
  
Write footer of empty disk to OSDisk  
  
PS C:\> $osDisk.ICloudBlob.WritePages($footerStream, $emptyDiskblob.Length - 512)  
  
PS C:\> Write-Output -InputObject "Removing empty disk blobs"  
  
Removing empty disk blobs  
  
PS C:\> $emptyDiskblob | Remove-AzStorageBlob -Force  
  
PS C:\> $NewDiskName = "$DiskName" + "-new"  
  
PS C:\> $NewDiskName  
testvm_OsDisk_1_93481399ceeb487e8ab46c4830ccc036-new  
  
PS C:\> $accountType = $Disk.Sku.Name  
  
PS C:\> $accountType  
Standard_LRS  
  
PS C:\> $vhdUri = $osdisk.ICloudBlob.Uri.AbsoluteUri  
  
PS C:\> $vhdUri  
https://shrinkc95365ba3f7498991f.blob.core.windows.net/shrinkc95365ba3f7498991f/testvm_OsDisk_1_93481399ceeb487e8ab46c4830ccc036.vhd  
  
PS C:\> $diskConfig = New-AzDiskConfig -AccountType $accountType -Location $VM.location -DiskSizeGB $DiskSizeGB -SourceUri $vhdUri -CreateOption Import -StorageAccountId $StorageAccount.Id -HyperVGeneration $HyperVGen  
  
PS C:\> $NewManagedDisk = New-AzDisk -DiskName $NewDiskName -Disk $diskConfig -ResourceGroupName $resourceGroupName  
  
PS C:\> $VM | Stop-AzVM -Force  
  
OperationId : 74c8ebee-160e-4673-9abb-6fc8847db2d4  
Status      : Succeeded  
StartTime   : 24-Feb-21 6:08:52 PM  
EndTime     : 24-Feb-21 6:09:03 PM  
Error       :   
  
PS C:\> Set-AzVMOSDisk -VM $VM -ManagedDiskId $NewManagedDisk.Id -Name $NewManagedDisk.Name  
  
  
ResourceGroupName   Name   Location       VmSize  OsType       NIC ProvisioningState Zone  
-----------------   ----   --------       ------  ------       --- ----------------- ----  
CXP               testvm westeurope Standard_B1s Windows testvm761         Succeeded       
  
  
PS C:\> Update-AzVM -ResourceGroupName $resourceGroupName -VM $VM  
  
RequestId IsSuccessStatusCode StatusCode ReasonPhrase  
--------- ------------------- ---------- ------------  
                         True         OK OK            
  
  
PS C:\> $VM | Start-AzVM  
  
OperationId : 3ae920a5-17c6-4ae9-9cf4-008048f11c15  
Status      : Succeeded  
StartTime   : 24-Feb-21 6:10:38 PM  
EndTime     : 24-Feb-21 6:14:31 PM  
Error       :   
  
  
PS C:\> $DiskName  
testvm_OsDisk_1_93481399ceeb487e8ab46c4830ccc036  
  
PS C:\> Remove-AzDisk -ResourceGroupName $resourceGroupName -DiskName $DiskName -Force;  
  
  
Name      : d7dacb0f-9842-4efd-a8af-921d9452d056  
StartTime : 24-Feb-21 6:18:12 PM  
EndTime   : 24-Feb-21 6:18:43 PM  
Status    : Succeeded  
Error     :   
  
  
PS C:\> $DiskName  
testvm_OsDisk_1_93481399ceeb487e8ab46c4830ccc036  
  
PS C:\> $osdisk | Remove-AzStorageBlob -Force  
  
PS C:\> $osdisk  
  
   AccountName: shrinkc95365ba3f7498991f, ContainerName: shrinkc95365ba3f7498991f  
  
Name                 BlobType  Length          ContentType                    LastModified         AccessTier SnapshotTime                 IsDeleted  VersionId                       
----                 --------  ------          -----------                    ------------         ---------- ------------                 ---------  ---------                       
testvm_OsDisk_1_9... PageBlob  136367309312    application/octet-stream       2021-02-24 10:37:51Z Unknown                                 False                                      
  
  
PS C:\> $StorageAccount | Remove-AzStorageAccount -Force  
  
PS C:\>

Before executing PS script:

After successful PS script execution:

------------------------------------------------------------------------------------------------------------------------------

Please "Accept the answer" if the information helped you. This will help us and others in the community as well.

MPVM 111 Reputation points

2021-02-24T16:36:52.357+00:00

Fantastic!
Many thanks for your confirmation and help.

Regards,

Answer 3

Andriy Bilous 12,076 MVP Volunteer Moderator

Hello @TechGuy_MS1

Shrink Azure VM disk size officially is not supported. However there are multiple workarounds
https://social.technet.microsoft.com/wiki/contents/articles/52487.azure-vm-decrease-the-disk-size.aspx
https://devblogs.microsoft.com/premier-developer/how-to-shrink-a-managed-disk/

Your link https://github.com/jrudlin/Azure/blob/master/General/Shrink-AzDisk.ps1 relates to the article https://jrudlin.github.io/2019-08-27-shrink-azure-vm-osdisk/
that clearly describes the disk resize process

TechGuy_MS1 61 Reputation points

2021-02-19T13:02:58.53+00:00

Hi @Andriy Bilous .,
Thanks for your early response. I will try your referred method, I hope I will work to reduce OS disk size.

Actually I am looking to know if the script mentioned in the above link is secure to run? Anything suspicious or problematic from safety and security of data?

Thanks.
TechGuy_MS1 61 Reputation points

2021-02-19T15:28:28.72+00:00

Hi @Andriy Bilous

In the method you referred, any idea how can I change or assign drive letter to the new volume from outside VM?

Thanks.
Andriy Bilous 12,076 Reputation points MVP Volunteer Moderator

2021-02-19T18:32:30.683+00:00

No way to do that outside of the VM
MPVM 111 Reputation points

2021-02-20T08:32:42.297+00:00

Ok. So is it possible to reduce OS disk size by this method? I am actually confused on the last part. After copying the disk, how to rename the disk volume to "C:\".

Thanks
nandakumar balasubramanian 1 Reputation point

2021-09-02T17:13:35.807+00:00

The link you shared talks about reducing data disk. Can we use the same for OS disk as well?

Share via

Powershell script to reduce OS disk size in Azure is safe to run?

2 additional answers

Your answer