Reducing size of Azure VM OS Disk for download/export

Question

I would like to create an Azure VM with a smaller OS disc than the default 127gb. I've been unable to find such an option in the Azure Portal, so I have attempted to shrink the disk. I have not been successful.

I understand I can trim (using the defragmentation tool) and shrink the volume (with Disk Management) but this won't change the "physical" size of the hard disk. That is, if I shrink the disk to 40gb, there will just be 87gb unallocated and the blob will still report 127gb.

What I am attempting to achieve is to shrink the blob to match the allocated space facilitating smaller downloads/exports of the VM image (e.g. 40 vs 127gb).

Any and all help is appreciated.

Answer 1

I'm still not 100% sure what was the magic criteria to make it work, but finally, I have a VM running with the reduced disk. Making it Gen1 was one. I tried many similar things and they all got stuck at boot time.

My way was:

1. Create the VM from the gallery images. For instance, Windows Server 2019 - Data Center. You'll have a 128 GB OS disk. Note: do not use the "smalldisk" version as it has no GUI.

2. Tweak the VM according to your needs. Here you can run the resize script. So, you'll end up with a ~90 GB unallocated space.

3. (Optional) Make a snapshot of this disk then make a disk from the snapshot. After some failed attempts, I started valuing the configured VM and didn't want to repeat the configuration. These options will be presented to you by the snapshot and by the disk.

4. Make a new vm from the disk. Check if it boots. Boot diagnostics show it rather quickly.

5. After stopping the new VM, look up the 3 (subscriptionID, diskID, vmName) required parameters for Sapnandu's script (Step 5. in his post) and execute the script in Azure Cloud Shell. (the icon in the header)

It takes time, about 10 minutes or so. When the script finished the new VM was running with the smaller disk.

So, there is a VM setup where the script works perfectly. Sapnandu's solution works. Many thanks!

Answer 2

In Azure if you create a VM it will create with some default configuration. At present it is not supported to reduce/shrink the OS disk (managed or unmanaged) size of an Azure VM from the Azure Portal (say from 128Gb to 32Gb for example), using the following process we can archive that, and cut down the disk cost.

Step 1. Open your VM and go to the Disk Management.

Step 2. Open PowerShell and execute the following command.

After successful execution you can find the following

Step 3. Now deallocate the VM from the Azure portal

Step 4. Now Go the Properties blade of the disk and copy the Resource ID

Step 5. Now execute the following PowerShell script from your local system. Must change $DiskID, $VMName, $AzSubscription with your value

    # Variables
$DiskID = ""# eg. "/subscriptions/203bdbf0-69bd-1a12-a894-a826cf0a34c8/resourcegroups/rg-server1-prod-1/providers/Microsoft.Compute/disks/Server1-Server1"
$VMName = "VM-Server1"
$DiskSizeGB = 32
$AzSubscription = "Prod Subscription"

# Script
# Provide your Azure admin credentials
Connect-AzAccount

#Provide the subscription Id of the subscription where snapshot is created
Select-AzSubscription -Subscription $AzSubscription

# VM to resize disk of
$VM = Get-AzVm | ? Name -eq $VMName

#Provide the name of your resource group where snapshot is created
$resourceGroupName = $VM.ResourceGroupName

# Get Disk from ID
$Disk = Get-AzDisk | ? Id -eq $DiskID

# Get VM/Disk generation from Disk
$HyperVGen = $Disk.HyperVGeneration

# Get Disk Name from Disk
$DiskName = $Disk.Name

# Get SAS URI for the Managed disk
$SAS = Grant-AzDiskAccess -ResourceGroupName $resourceGroupName -DiskName $DiskName -Access 'Read' -DurationInSecond 600000;

#Provide the managed disk name
#$managedDiskName = "yourManagedDiskName" 

#Provide Shared Access Signature (SAS) expiry duration in seconds e.g. 3600.
#$sasExpiryDuration = "3600"

#Provide storage account name where you want to copy the snapshot - the script will create a new one temporarily
$storageAccountName = "shrink" + [system.guid]::NewGuid().tostring().replace('-','').substring(1,18)

#Name of the storage container where the downloaded snapshot will be stored
$storageContainerName = $storageAccountName

#Provide the key of the storage account where you want to copy snapshot. 
#$storageAccountKey = "yourStorageAccountKey"

#Provide the name of the VHD file to which snapshot will be copied.
$destinationVHDFileName = "$($VM.StorageProfile.OsDisk.Name).vhd"

#Generate the SAS for the managed disk
#$sas = Grant-AzureRmDiskAccess -ResourceGroupName $resourceGroupName -DiskName $managedDiskName -Access Read -DurationInSecond $sasExpiryDuration

#Create the context for the storage account which will be used to copy snapshot to the storage account 
$StorageAccount = New-AzStorageAccount -ResourceGroupName $resourceGroupName -Name $storageAccountName -SkuName Standard_LRS -Location $VM.Location
$destinationContext = $StorageAccount.Context
$container = New-AzStorageContainer -Name $storageContainerName -Permission Off -Context $destinationContext

#Copy the snapshot to the storage account and wait for it to complete
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

# Revoke SAS token
Revoke-AzDiskAccess -ResourceGroupName $resourceGroupName -DiskName $DiskName

# Emtpy disk to get footer from
$emptydiskforfootername = "$($VM.StorageProfile.OsDisk.Name)-empty.vhd"

# Empty disk URI
#$EmptyDiskURI = $container.CloudBlobContainer.Uri.AbsoluteUri + "/" + $emptydiskforfooter

$diskConfig = New-AzDiskConfig `
    -Location $VM.Location `
    -CreateOption Empty `
    -DiskSizeGB $DiskSizeGB `
    -HyperVGeneration $HyperVGen

$dataDisk = New-AzDisk `
    -ResourceGroupName $resourceGroupName `
    -DiskName $emptydiskforfootername `
    -Disk $diskConfig

$VM = Add-AzVMDataDisk `
    -VM $VM `
    -Name $emptydiskforfootername `
    -CreateOption Attach `
    -ManagedDiskId $dataDisk.Id `
    -Lun 63

Update-AzVM -ResourceGroupName $resourceGroupName -VM $VM

$VM | Stop-AzVM -Force


# Get SAS token for the empty disk
$SAS = Grant-AzDiskAccess -ResourceGroupName $resourceGroupName -DiskName $emptydiskforfootername -Access 'Read' -DurationInSecond 600000;

# Copy the empty disk to blob storage
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

# Revoke SAS token
Revoke-AzDiskAccess -ResourceGroupName $resourceGroupName -DiskName $emptydiskforfootername

# Remove temp empty disk
Remove-AzVMDataDisk -VM $VM -DataDiskNames $emptydiskforfootername
Update-AzVM -ResourceGroupName $resourceGroupName -VM $VM

# Delete temp disk
Remove-AzDisk -ResourceGroupName $resourceGroupName -DiskName $emptydiskforfootername -Force;

# Get the blobs
$emptyDiskblob = Get-AzStorageBlob -Context $destinationContext -Container $storageContainerName -Blob $emptydiskforfootername
$osdisk = Get-AzStorageBlob -Context $destinationContext -Container $storageContainerName -Blob $destinationVHDFileName

$footer = New-Object -TypeName byte[] -ArgumentList 512
write-output "Get footer of empty disk"

$downloaded = $emptyDiskblob.ICloudBlob.DownloadRangeToByteArray($footer, 0, $emptyDiskblob.Length - 512, 512)

$osDisk.ICloudBlob.Resize($emptyDiskblob.Length)
$footerStream = New-Object -TypeName System.IO.MemoryStream -ArgumentList (,$footer)
write-output "Write footer of empty disk to OSDisk"
$osDisk.ICloudBlob.WritePages($footerStream, $emptyDiskblob.Length - 512)

Write-Output -InputObject "Removing empty disk blobs"
$emptyDiskblob | Remove-AzStorageBlob -Force


#Provide the name of the Managed Disk
$NewDiskName = "$DiskName" + "-new"

#Create the new disk with the same SKU as the current one
$accountType = $Disk.Sku.Name

# Get the new disk URI
$vhdUri = $osdisk.ICloudBlob.Uri.AbsoluteUri

# Specify the disk options
$diskConfig = New-AzDiskConfig -AccountType $accountType -Location $VM.location -DiskSizeGB $DiskSizeGB -SourceUri $vhdUri -CreateOption Import -StorageAccountId $StorageAccount.Id -HyperVGeneration $HyperVGen

#Create Managed disk
$NewManagedDisk = New-AzDisk -DiskName $NewDiskName -Disk $diskConfig -ResourceGroupName $resourceGroupName

$VM | Stop-AzVM -Force

# Set the VM configuration to point to the new disk  
Set-AzVMOSDisk -VM $VM -ManagedDiskId $NewManagedDisk.Id -Name $NewManagedDisk.Name

# Update the VM with the new OS disk
Update-AzVM -ResourceGroupName $resourceGroupName -VM $VM

$VM | Start-AzVM

start-sleep 180
# Please check the VM is running before proceeding with the below tidy-up steps

# Delete old Managed Disk
Remove-AzDisk -ResourceGroupName $resourceGroupName -DiskName $DiskName -Force;

# Delete old blob storage
$osdisk | Remove-AzStorageBlob -Force

# Delete temp storage account
$StorageAccount | Remove-AzStorageAccount -Force

Answer 3

I have written a blog post detailing this answer in full. But the main issue here was being able to reduce the size of the Azure VM which defaults to 127gb in order to allow for fasted export/download. The way I have achieved this is by trimming the hard drive and then using Disk2VHD to create a VHD file of the running VM. Disk2VHD will create an expandable disk that is only as large as the current data on the disc, not the entire available disk. In my case 40gb vs 127gb. If one saves this VHD file to an attached disk (read: blob storage) it can be easily downloaded via HTTP by your entire team. Thus, the download is now 40gbs instead of 127gbs. For more, please read my detailed blog post:

http://www.kevinmcloutier.com/?p=263

Original link no longer works: https://web.archive.org/web/20161027213258/http://kevinmcloutier.com/post/4

Answer 4

You would have to create your own VM image and then deploy using that. This template shows you how to deploy using your own image.

https://github.com/Azure/azure-quickstart-templates/tree/master/101-vm-from-user-image

Currently, the images in the gallery are all 127gb. Since Azure VMs only used fixed size discs, you can't just select the size.