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

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's 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:

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Prerequisites

• If you prefer to run CLI reference commands locally, install the Azure CLI. If you're running on Windows or macOS, consider running Azure CLI in a Docker container. For more information, see How to run the Azure CLI in a Docker container.

  • If you're using a local installation, sign in to the Azure CLI by using the az login command. To finish the authentication process, follow the steps displayed in your terminal. For other sign-in options, see Sign in with the Azure CLI.

  • When you're prompted, install the Azure CLI extension on first use. For more information about extensions, see Use extensions with the Azure CLI.

  • Run az version to find the version and dependent libraries that are installed. To upgrade to the latest version, run az upgrade.

• This article requires version 2.0.29 or later of the Azure CLI.

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. Temporary disks are high-performance disks and might 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 up to an absolute maximum of 64 disks per virtual machine.

VM disk types

Azure provides two types of disk.

Standard disk

Standard Storage is backed by HDDs, and delivers cost-effective storage and performance. Standard disks are ideal for a cost effective dev and test workload.

Premium disk

Premium disks are backed by SSD-based high-performance, low-latency disk. These disks are recommended for VMs that run production workloads. Premium Storage supports DS-series, DSv2-series, GS-series, and FS-series VMs. When you select a disk size, the value is rounded up to the next type. For example, if the disk size is less than 128 GB, the disk type is P10. If the disk size is between 129 GB and 512 GB, the size is a P20. Over, 512 GB, the size is a P30.

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

First, create a resource group with the az group create command. In this example, a resource group named myResourceGroup is created in the chinanorth2 region.

az group create --name myResourceGroup --location chinanorth2

Create a Virtual Machine Scale Set with the az vmss create command. The following example creates a scale set named myScaleSet, and generates SSH keys if they don't exist. Two disks are created with the --data-disk-sizes-gb parameter. The first disk is 64 GB in size, and the second disk is 128 GB:

az vmss create \
  --resource-group myResourceGroup \
  --name myScaleSet \
  --image Ubuntu2204 \
  --orchestration-mode Flexible \
  --admin-username azureuser \
  --generate-ssh-keys \
  --data-disk-sizes-gb 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 additional disks to each instance in an existing scale set. Use the scale set created in the previous step to add another disk with az vmss disk attach. The following example attaches an additional 128 GB disk:

az vmss disk attach \
  --resource-group myResourceGroup \
  --vmss-name myScaleSet \
  --size-gb 128

Alternatively, if you want to add a data disk to an individual instance in a scale set, use az vm disk attach.

az vm disk attach \
  --vm-name myScaleSet_Instance1 \
  --resource-group myResourceGroup \
  --size-gb 30 \
  --name disk_name \
  --new

List attached disks

To view information about disks attached to a scale set, use az vmss show and query on virtualMachineProfile.storageProfile.dataDisks:

az vmss show \
  --resource-group myResourceGroup \
  --name myScaleSet \
  --query virtualMachineProfile.storageProfile.dataDisks

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:

[
  {
    "additionalProperties": {},
    "caching": "None",
    "createOption": "Empty",
    "diskSizeGb": 64,
    "lun": 0,
    "managedDisk": {
      "additionalProperties": {},
      "storageAccountType": "StandardSSD_LRS"
    },
    "name": null
  },
  {
    "additionalProperties": {},
    "caching": "None",
    "createOption": "Empty",
    "diskSizeGb": 128,
    "lun": 1,
    "managedDisk": {
      "additionalProperties": {},
      "storageAccountType": "StandardSSD_LRS"
    },
    "name": null
  },
  {
    "additionalProperties": {},
    "caching": "None",
    "createOption": "Empty",
    "diskSizeGb": 128,
    "lun": 2,
    "managedDisk": {
      "additionalProperties": {},
      "storageAccountType": "StandardSSD_LRS"
    },
    "name": null
  }
]

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 az vmss disk detach and specify the LUN of the disk. The LUNs are shown in the output from az vmss show in the previous section. The following example detaches LUN 2 from the scale set:

az vmss disk detach \
  --resource-group myResourceGroup \
  --name myScaleSet \
  --lun 2

You can also use az vm disk detach to detach a disk from an individual instance.

az vm disk detach \
  --vm-name myScaleSet_Instance1
  --name disk_name

Clean up resources

To remove your scale set and disks, delete the resource group and all its resources with az group delete. The --no-wait parameter returns control to the prompt without waiting for the operation to complete. The --yes parameter confirms that you wish to delete the resources without an additional prompt to do so.

az group delete --name myResourceGroup --no-wait --yes

Next steps

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

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