I want to know why resize a datadisk attached to a running VM by terraform cause the VM to reboot?

Question

My VM and datadisk fulfill the requirement to expand without downtime https://learn.microsoft.com/en-us/azure/virtual-machines/windows/expand-os-disk#expand-without-downtime.

VM information: Standard F8s v2 (8 vcpus, 16 GiB memory), Windows (Windows Server 2019 Datacenter),Microsoft.Compute/virtualMachines.

Datadisk information: Standard HDD LRS 256GB 500 IOPS 60 Max through put Encyption SSE with PMK

So WHY it reboot the VM when I change only the disk size from terraform?

Thankyou for your answers in advance!

Answer 1

Hello Hoàng Ân

In Azure, changing the size of an OS disk typically does not require a VM reboot when done through the Azure Portal or Azure CLI . However, Terraform behaves differently due to the way it handles disk resizing operations.

This feature has the limitations on this to the below

• Install and use either:
  • The latest Azure CLI
  • The latest Azure PowerShell module
  • The Azure portal
  • Or an Azure Resource Manager template with an API version that's 2021-04-01 or newer.

To avoid a reboot, the disk resize operation needs to be perceived by Terraform as a non-disruptive change or run using CLI commands.

Please let me know if you have further questions

You can mark it 'Accept Answer' if this helped.