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Tutorial: Create and use disks with Virtual Machine Scale Set with Azure PowerShell

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Virtual Machine Scale Sets use disks to store the VM instance's operating system, applications, and data. As you create and manage a scale set, it is important to choose a disk size and configuration appropriate to the expected workload. This tutorial covers how to create and manage VM disks. In this tutorial you learn about:

  • OS disks and temporary disks
  • Data disks
  • Standard and Premium disks
  • Disk performance
  • Attach and prepare data disks

If you don't have an Azure subscription, create a free account before you begin.

Azure Cloud Shell

Azure hosts Azure Cloud Shell, an interactive shell environment that you can use through your browser. You can use either Bash or PowerShell with Cloud Shell to work with Azure services. You can use the Cloud Shell preinstalled commands to run the code in this article, without having to install anything on your local environment.

To start Azure Cloud Shell:

Option Example/Link
Select Try It in the upper-right corner of a code or command block. Selecting Try It doesn't automatically copy the code or command to Cloud Shell. Screenshot that shows an example of Try It for Azure Cloud Shell.
Go to https://shell.azure.com, or select the Launch Cloud Shell button to open Cloud Shell in your browser. Button to launch Azure Cloud Shell.
Select the Cloud Shell button on the menu bar at the upper right in the Azure portal. Screenshot that shows the Cloud Shell button in the Azure portal

To use Azure Cloud Shell:

  1. Start Cloud Shell.

  2. Select the Copy button on a code block (or command block) to copy the code or command.

  3. Paste the code or command into the Cloud Shell session by selecting Ctrl+Shift+V on Windows and Linux, or by selecting Cmd+Shift+V on macOS.

  4. Select Enter to run the code or command.

Default Azure disks

When a scale set is created or scaled, two disks are automatically attached to each VM instance.

Operating system disk - Operating system disks can be sized up to 2 TB, and hosts the VM instance's operating system. The OS disk is labeled /dev/sda by default. The disk caching configuration of the OS disk is optimized for OS performance. Because of this configuration, the OS disk should not host applications or data. For applications and data, use data disks, which are detailed later in this article.

Temporary disk - Temporary disks use a solid-state drive that is located on the same Azure host as the VM instance. These are high-performance disks and can be used for operations such as temporary data processing. However, if the VM instance is moved to a new host, any data stored on a temporary disk is removed. The size of the temporary disk is determined by the VM instance size. Temporary disks are labeled /dev/sdb and have a mountpoint of /mnt.

Azure data disks

Additional data disks can be added if you need to install applications and store data. Data disks should be used in any situation where durable and responsive data storage is desired. Each data disk has a maximum capacity of 4 TB. The size of the VM instance determines how many data disks can be attached. For each VM vCPU, two data disks can be attached.

VM disk types

The following table provides a comparison of the five disk types to help you decide which to use.

Ultra disk Premium SSD v2 Premium SSD Standard SSD Standard HDD
Disk type SSD SSD SSD SSD HDD
Scenario IO-intensive workloads such as SAP HANA, top tier databases (for example, SQL, Oracle), and other transaction-heavy workloads. Production and performance-sensitive workloads that consistently require low latency and high IOPS and throughput Production and performance sensitive workloads Web servers, lightly used enterprise applications and dev/test Backup, non-critical, infrequent access
Max disk size 65,536 GiB 65,536 GiB 32,767 GiB 32,767 GiB 32,767 GiB
Max throughput 4,000 MB/s 1,200 MB/s 900 MB/s 750 MB/s 500 MB/s
Max IOPS 160,000 80,000 20,000 6,000 2,000, 3,000*
Usable as OS Disk? No No Yes Yes Yes

*Only applies to disks with performance plus (preview) enabled.

For a video that covers some high level differences for the different disk types, as well as some ways for determining what impacts your workload requirements, see Block storage options with Azure Disk Storage and Elastic SAN.

Create and attach disks

You can create and attach disks when you create a scale set, or with an existing scale set.

As of API version 2019-07-01, you can set the size of the OS disk in a Virtual Machine Scale Set with the storageProfile.osDisk.diskSizeGb property. After provisioning, you might have to expand or repartition the disk to make use of the whole space. Learn more about how to expand the volume in your OS in either Windows or Linux.

Attach disks at scale set creation

Create a Virtual Machine Scale Set with New-AzVmss. When prompted, provide a username and password for the VM instances. To distribute traffic to the individual VM instances, a load balancer is also created. The load balancer includes rules to distribute traffic on TCP port 80, as well as allow remote desktop traffic on TCP port 3389 and PowerShell remoting on TCP port 5985.

Two disks are created with the -DataDiskSizeGb parameter. The first disk is 64 GB in size, and the second disk is 128 GB. When prompted, provide your own desired administrative credentials for the VM instances in the scale set:

New-AzResourceGroup -Name "myResourceGroup" -Location "East US"

New-AzVmss `
  -ResourceGroupName "myResourceGroup" `
  -Location "EastUS" `
  -OrchestrationMode "Flexible" `
  -VMScaleSetName "myScaleSet" `
  -VirtualNetworkName "myVnet" `
  -SubnetName "mySubnet" `
  -PublicIpAddressName "myPublicIPAddress" `
  -LoadBalancerName "myLoadBalancer" `
  -DataDiskSizeInGb 64,128

It takes a few minutes to create and configure all the scale set resources and VM instances.

Attach a disk to existing scale set

You can also attach disks to an existing scale set. Use the scale set created in the previous step to add another disk with Add-AzVmssDataDisk. The following example attaches an additional 128 GB disk to an existing scale set:

# Get scale set object
$vmss = Get-AzVmss `
  -ResourceGroupName "myResourceGroup" `
  -VMScaleSetName "myScaleSet"

# Attach a 128 GB data disk to LUN 2
Add-AzVmssDataDisk `
  -VirtualMachineScaleSet $vmss `
  -CreateOption Empty `
  -Lun 2 `
  -DiskSizeGB 128

# Update the scale set to apply the change
Update-AzVmss `
  -ResourceGroupName "myResourceGroup" `
  -VMScaleSetName "myScaleSet" `
  -VirtualMachineScaleSet $vmss

Alternatively, if you want to add a data disk to an individual instance in a scale set, use Add-AzVmssVMDataDisk.

$VirtualMachine = Get-AzVmssVM -ResourceGroupName "myResourceGroup" -VMScaleSetName "myScaleSet" -InstanceId 1
Add-AzVmssVMDataDisk -VirtualMachineScaleSetVM $VirtualMachine -LUN 2 -DiskSizeInGB 1 -CreateOption Empty -StorageAccountType Standard_LRS
Update-AzVmssVM -VirtualMachineScaleSetVM $VirtualMachine

List attached disks

To view information about disks attached to a scale set, use Get-AzVmss as follows:

Get-AzVmss -ResourceGroupName "myResourceGroup" -Name "myScaleSet"

Under the VirtualMachineProfile.StorageProfile property, the list of DataDisks is shown. Information on the disk size, storage tier, and LUN (Logical Unit Number) is shown. The following example output details the three data disks attached to the scale set:

DataDisks[0]                            :
  Lun                                   : 0
  Caching                               : None
  CreateOption                          : Empty
  DiskSizeGB                            : 64
  ManagedDisk                           :
    StorageAccountType                  : PremiumLRS
DataDisks[1]                            :
  Lun                                   : 1
  Caching                               : None
  CreateOption                          : Empty
  DiskSizeGB                            : 128
  ManagedDisk                           :
    StorageAccountType                  : PremiumLRS
DataDisks[2]                            :
  Lun                                   : 2
  Caching                               : None
  CreateOption                          : Empty
  DiskSizeGB                            : 128
  ManagedDisk                           :
    StorageAccountType                  : PremiumLRS

Detach a disk

When you no longer need a given disk, you can detach it from the scale set. The disk is removed from all VM instances in the scale set. To detach a disk from a scale set, use Remove-AzVmssDataDisk and specify the LUN of the disk. The LUNs are shown in the output from Get-AzVmss in the previous section. The following example detaches LUN 3 from the scale set:

# Get scale set object
$vmss = Get-AzVmss `
  -ResourceGroupName "myResourceGroup" `
  -VMScaleSetName "myScaleSet"

# Detach a disk from the scale set
Remove-AzVmssDataDisk `
  -VirtualMachineScaleSet $vmss `
  -Lun 2

# Update the scale set and detach the disk from the VM instances
Update-AzVmss `
  -ResourceGroupName "myResourceGroup" `
  -VMScaleSetName "myScaleSet" `
  -VirtualMachineScaleSet $vmss

Alternatively, if you want to remove a data disk to an individual instance in a scale set, use Remove-AzVmssVMDataDisk.

$VirtualMachine = Get-AzVmssVM -ResourceGroupName "myResourceGroup" -VMScaleSetName "myScaleSet" -InstanceId "c91dfbd9"
Remove-AzVmssVMDataDisk -VirtualMachineScaleSetVM $VirtualMachine -Lun 2
Update-AzVmssVM -VirtualMachineScaleSetVM -VM $VirtualMachine

Clean up resources

To remove your scale set and disks, delete the resource group and all its resources with Remove-AzResourceGroup. The -Force parameter confirms that you wish to delete the resources without an additional prompt to do so. The -AsJob parameter returns control to the prompt without waiting for the operation to complete.

Remove-AzResourceGroup -Name "myResourceGroup" -Force -AsJob

Next steps

In this tutorial, you learned how to create and use disks with scale sets with Azure PowerShell:

  • OS disks and temporary disks
  • Data disks
  • Standard and Premium disks
  • Disk performance
  • Attach and prepare data disks

Advance to the next tutorial to learn how to use a custom image for your scale set VM instances.

Use a custom image for scale set VM instances