Azure CLI - How to update cache setting of a live managed data disk attached to an Azure VM

Question

Need some help figuring out the Azure CLI command and parameters to update cache setting of a live managed data disk attached to an Azure VM.

A managed data disk is created and attached to an Azure VM outside of my control. By default, Host caching is set to Read-Only . For some performance reasons, I would like to set Host caching to None for the attached data disk.

What did I try?

1. Tried to use below command

az vm update --subscription my-subscription --name my-vm-name --resource-group my-rgroup-name --disk-caching os=ReadWrite

This command updates the OS Disks Host cache setting. However, could not update managed disks setting. I tried different keys like managed, data-disks, attached, etc... instead of os in os=ReadWrite ; Nothing worked, command throws ValueError

ValueError: invalid literal for int() with base 10: 'data-disks'

2. Explored another command - az disk update . However, it does not have option to update managed disk cache setting.

3. Tried to detach and re-attach the managed disk with --caching set to None . It works. However, this is not permitted in my case.

az vm disk detach --subscription my-subscription -g my-rgroup-name --vm-name my-vm-name --name managed-disk-name

az vm disk attach --subscription my-subscription -g my-rgroup-name --vm-name my-vm-name --name managed-disk-name --caching none

Need this for automation. So changing this setting from Azure portal UI is not an option.

Suggestions are much appreciated.

Answer 1

Without detaching the disk from virtual Machine using the below cmdlet to change the managed disk caching from ReadWrite\\ReadOnly to None .

We have tested this cmdlet in our environment by creating a VirtualMachine & attached a Data disk to it and it is working fine.

Here is the Cmdlet:

az vm update --resource-group <resource-group-name> --name <vmName> --disk-caching os=ReadWrite 0(LunNumberOfTheDisk)=None

Here is the sample output screenshot for reference :

1. Below screenshot show the current state of disk caching before executing the above cmdlet.

2. In the below screenshot , you can see we have executed the cmdlet without stopping or detaching the disk from the virtual machine and the operation got succeeded without any interruption.