Tutorial - Manage Azure disks with the Azure CLI

Applies to: ✔️ Linux VMs ✔️ Flexible scale sets

Azure virtual machines (VMs) use disks to store the operating system, applications, and data. When you create a VM, it is important to choose a disk size and configuration appropriate to the expected workload. This tutorial shows you how to deploy and manage VM disks. You learn about:

Default Azure disks

When an Azure virtual machine is created, two disks are automatically attached to the virtual machine.

Operating system disk - The operating system (OS) disk hosts the VM operating system and can be up to 4,095 gibibytes (GiB), although many operating systems are partitioned with master boot records (MBRs) by default. An MBR limits the usable size to 2 TiB. If you need more than 2 TiB, create and attach data disks and use them for data storage. Device names vary by VM generation and disk controller type, so don't rely on a fixed path such as /dev/sda. OS disk caching is optimized for OS performance, so don't store application data on the OS disk. Use data disks for application and data storage.

Temporary disk - Temporary storage uses local storage on the same Azure host as the VM. Depending on the VM size and generation, this storage might appear as a temporary disk or local NVMe disk. It's high-performance, but nonpersistent. If the VM is moved to a new host, data on temporary storage is removed. The available size depends on the VM size.

data disks

To install applications and store data, additional data disks can be added. Data disks should be used in any situation where durable and responsive data storage is desired. The size of the virtual machine determines how many data disks can be attached to a VM.

VM disk types

Azure managed disks offer five disk types:

• Ultra Disks
• Premium SSD v2
• Premium SSDs
• Standard SSDs
• Standard HDDs

In general, use Premium SSD v2 or Premium SSD for production workloads, Standard SSD for dev/test and less performance-sensitive workloads, and Ultra Disks for IO-intensive data workloads. Ultra Disks and Premium SSD v2 are data-disk only options and can't be used as OS disks. For detailed limits, region availability, and sizing guidance, see Azure managed disk types.

Launch Azure Cloud Shell

Azure Cloud Shell is a free interactive shell that you can use to run the steps in this article. It has common Azure tools preinstalled and configured to use with your account.

To open Cloud Shell, select Try it from the upper-right corner of a code block. You can also launch Cloud Shell in a separate browser tab at https://shell.azure.com. Select Copy to copy a code block, paste it into Cloud Shell, and press Enter to run it.

Create and attach disks

Data disks can be created and attached at VM creation time or to an existing VM.

Attach disk at VM creation

Create a resource group with the az group create command.

az group create --name myResourceGroupDisk --location eastus

Create a VM using the az vm create command. The following example creates a VM named myVM, adds a user account named azureuser, and generates SSH keys if they don't already exist. The --data-disk-sizes-gb argument specifies additional data disks to create and attach. To create and attach more than one disk, use a space-delimited list of disk sizes. In the following example, a VM is created with two data disks, both 128 GB. Because the disk sizes are 128 GB, these disks are both configured as P10s, which provide maximum 500 IOPS per disk.

az vm create \
  --resource-group myResourceGroupDisk \
  --name myVM \
  --image Ubuntu2204 \
  --size Standard_DS2_v2 \
  --admin-username azureuser \
  --generate-ssh-keys \
  --data-disk-sizes-gb 128 128

Attach disk to existing VM

To create and attach a new disk to an existing virtual machine, use the az vm disk attach command. The following example creates a premium disk, 128 gigabytes in size, and attaches it to the VM created in the last step.

az vm disk attach \
    --resource-group myResourceGroupDisk \
    --vm-name myVM \
    --name myDataDisk \
    --size-gb 128 \
    --sku Premium_LRS \
    --new

Prepare data disks

Once a disk has been attached to the virtual machine, the operating system needs to be configured to use the disk. The following example shows how to manually configure a disk. This process can also be automated using cloud-init, which is covered in a later tutorial.

Create an SSH connection with the virtual machine. Replace the example IP address with the public IP of the virtual machine.

ssh azureuser@10.101.10.10

Partition the disk with parted.

sudo parted /dev/sdc --script mklabel gpt mkpart xfspart xfs 0% 100%

Write a file system to the partition by using the mkfs command. Use partprobe to make the OS aware of the change.

sudo mkfs.xfs /dev/sdc1
sudo partprobe /dev/sdc1

Mount the new disk so that it is accessible in the operating system.

sudo mkdir /datadrive && sudo mount /dev/sdc1 /datadrive

The disk can now be accessed through the /datadrive mountpoint, which can be verified by running the df -h command.

df -h | grep -i "sd"

The output shows the new drive mounted on /datadrive.

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        29G  2.0G   27G   7% /
/dev/sda15      105M  3.6M  101M   4% /boot/efi
/dev/sdb1        14G   41M   13G   1% /mnt
/dev/sdc1        50G   52M   47G   1% /datadrive

To ensure that the drive is remounted after a reboot, it must be added to the /etc/fstab file. To do so, get the UUID of the disk with the blkid utility.

sudo -i blkid

The output displays the UUID of the drive, /dev/sdc1 in this case.

/dev/sdc1: UUID="33333333-3b3b-3c3c-3d3d-3e3e3e3e3e3e" TYPE="xfs"

Open the /etc/fstab file in a text editor as follows:

sudo nano /etc/fstab

Add a line similar to the following to the /etc/fstab file, replacing the UUID value with your own.

UUID=33333333-3b3b-3c3c-3d3d-3e3e3e3e3e3e   /datadrive  xfs    defaults,nofail   1  2

When you are done editing the file, use Ctrl+O to write the file and Ctrl+X to exit the editor.

Now that the disk has been configured, close the SSH session.

exit

Take a disk snapshot

When you take a disk snapshot, Azure creates a read-only, point-in-time copy of the disk. Azure VM snapshots are useful to quickly save the state of a VM before you make configuration changes. In the event of an issue or error, you can restore a VM by using a snapshot. When a VM has more than one disk, a snapshot is taken of each disk independently. To take application-consistent backups, consider stopping the VM before you take disk snapshots. Alternatively, use Azure Backup, which supports automated backups while the VM is running.

Create snapshot

Before you create a snapshot, you need the ID or name of the disk. Use az vm show to show the disk ID. In this example, the disk ID is stored in a variable so that it can be used in a later step.

osdiskid=$(az vm show \
   -g myResourceGroupDisk \
   -n myVM \
   --query "storageProfile.osDisk.managedDisk.id" \
   -o tsv)

Now that you have the ID, use az snapshot create to create a snapshot of the disk.

az snapshot create \
    --resource-group myResourceGroupDisk \
    --source "$osdiskid" \
    --name osDisk-backup

Create disk from snapshot

This snapshot can then be converted into a disk using az disk create, which can be used to recreate the virtual machine.

az disk create \
   --resource-group myResourceGroupDisk \
   --name mySnapshotDisk \
   --source osDisk-backup

Restore virtual machine from snapshot

To demonstrate virtual machine recovery, delete the existing virtual machine using az vm delete.

az vm delete \
--resource-group myResourceGroupDisk \
--name myVM

Create a new virtual machine from the snapshot disk.

az vm create \
    --resource-group myResourceGroupDisk \
    --name myVM \
    --attach-os-disk mySnapshotDisk \
    --os-type linux

Reattach data disk

All data disks need to be reattached to the virtual machine.

Find the data disk name using the az disk list command. This example places the name of the disk in a variable named datadisk, which is used in the next step.

datadisk=$(az disk list \
   -g myResourceGroupDisk \
   --query "[?contains(name,'myVM')].[id]" \
   -o tsv)

Use the az vm disk attach command to attach the disk.

az vm disk attach \
   --resource-group myResourceGroupDisk \
   --vm-name myVM \
   --name $datadisk

Next steps

In this tutorial, you learned about VM disks topics such as:

Advance to the next tutorial to learn about automating VM configuration.