What are the performance and cost advantages of using Ephemeral OS disks for our Windows virtual machine hosts in Azure?

Hi SRR Shinka

When you're designing Azure Virtual Desktop hosts as truly stateless machines, Ephemeral OS disks can be a great fit. Since your users' profiles are already being redirected through FSLogix and their files are stored in OneDrive, there's very little value in maintaining a persistent OS disk between VM lifecycles. The biggest advantage is performance Ephemeral OS disks are stored on the VM's local storage, so provisioning, reimaging, and scaling operations are significantly faster than with managed disks. This allows AVD session hosts to be deployed or refreshed much more quickly, which is especially useful in autoscaling scenarios where capacity needs to expand rapidly during peak demand.

From a cost perspective, you also eliminate the managed OS disk charges because the operating system resides on the host's local storage rather than Azure Storage. Another benefit is simplified lifecycle management; if a VM becomes unhealthy, you can simply redeploy it from your golden image instead of troubleshooting and preserving the existing OS state. The tradeoff, of course, is that any changes made to the local OS disk are lost when the VM is deallocated or recreated, but in a properly designed non-persistent AVD environment, that's typically the desired behavior.

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