What Are Ephemeral OS Disks?

Ephemeral means short-lived. In Azure, an Ephemeral OS Disk is stored on the local temporary storage of the physical host instead of a managed disk. This provides low latency, high IOPS, and zero OS disk cost. However, the OS disk is deleted when the VM is deallocated.

Why Use Ephemeral OS Disks?

They offer faster performance, quicker provisioning, and cost savings. They’re ideal for stateless workloads like scale sets or pooled session hosts in Azure Virtual Desktop.

Limitations and Considerations

When working with ephemeral disks, it’s essential to be aware of the specific restrictions. These limitations include the following:

Cannot capture VM image
No snapshots
No Azure Backup
No Azure Site Recovery
No Azure Disk Encryption
Limited management in the Azure Portal

Additionally, the VM should be provisioned with sufficient local temporary storage to accommodate the operating system image. Generally, this requires 127 GB for Windows environments and 30 GB for Linux systems.

Deploying via Azure Portal

Below are the steps to configure Azure virtual machines through the portal with ephemeral disks. Ensure that the selected VM SKU provides sufficient local temporary disk capacity to meet the operating system requirements.

Create a new VM in the Azure Portal
Choose a VM size that supports Ephemeral OS Disks
Under Disks > Advanced, select Ephemeral OS Disk placement (Temp or NVMe)
Complete the configuration and deploy

🎥 Watch the video above for a step-by-step guide on how to deploy virtual machines using ephemeral OS disks, both through the Azure portal and with PowerShell.

Deploying via PowerShell

It is possible to create ephemeral OS disks using PowerShell, Bicep, Azure CLI, or Terraform. The following is a sample Set-AzMVOSdisk command that sets up ephemeral disks on a VM with NVMe temporary storage support. For the complete instructions on creating an Azure VM with an ephemeral OS disk, refer to the GitHub link below.

Set-AzVMOSDisk -VM $vmConfig -Name 'osdisk' -CreateOption FromImage -Caching ReadOnly -DiffDiskSetting Local -DiffDiskPlacement NVMeDisk

Ephemeral OS Disks are a great way to optimize Azure VM performance and reduce costs for the right workloads. Watch the full tutorial video for a detailed walkthrough and best practices.