How To Convert A Virtual Machine’s Disk Tiers

Note that this post is based on managed disks – anyone using un-managed disks should upgrade to managed disks because un-managed disks are no longer being improved. You can learn more here:

• Converting Azure VM Disks to Managed Disks
• Converting Availability Set Virtual Machines to Azure Managed Disks

The Process

How you will do the conversion will depend on the type of virtual machine that you have and the tier of disk that you want to convert to:

• Standard HDD: Can be associated with any kind of virtual machine.
• Standard SSD: Also can be associated with any kind of virtual machine.
• Premium SSD: Can only be associated with virtual machines with the “S” specialization.

For example, if I want to convert a disk of an A_v2-Series virtual machine to Standard SSD then there will be no change required to the virtual machine. However, if I want to change the disk to a Premium SSD, I would have to convert the machine to something like a DS_v3 or FS_v2 virtual machine.
So this means there are two possible conversion processes. If your desired disk tier is supported by the virtual machine’s current specification then you will:

1. Shut down the virtual machine
2. Change the series of the virtual machine
3. Change the disk tier
4. Start up the virtual machine

If your desired tier is not supported by the machine then you will:

1. Shut down the virtual machine
2. Change the disk tier
3. Start up the virtual machine

While the human act of changing a disk tier is instant, the result, which is done in the background while the machine is running, takes some time; you will notice a gradual change in the disk’s performance over time.

Change the Virtual Machine

If your virtual machine cannot support the desired disk tier, then you will do this process first. Start by shutting down the virtual machine – if you don’t do this you will have limited conversion options and a shutdown is required to modify the disk tier anyway. Then open the virtual machine in the Azure Portal and click Size under Settings. Choose the desired series/size/specialization – you might need to adjust the filters at the top to reveal otherwise hidden options.

Click Resize after you select the size. You will have to wait for the resize action to complete.

Change the Disk Tier

Make sure that the virtual machine is (still) shut down. Open the disk that you want to modify the tier of. Browse to Configuration under Settings. Click Account Type, select the desired tier, and click Save.

Wait for the save job to complete and then restart the virtual machine.
Note that the tier change is not instant. You can start the virtual machine immediately, even if you just changed the series of the virtual machine. Something like a Hyper-V storage live migration is happening in the background and the performance traits of the disk will change as the disk contents migrate from the old tier to the new tier.