Inspect image size and placement when an ephemeral OS option is unavailable

Source facts

Microsoft says a disabled ephemeral-disk or placement option can indicate that the chosen VM size lacks sufficient cache or temporary-disk capacity for the OS image, or lacks Premium storage support. The portal’s disk settings offer OS cache, temporary disk, or NVMe placement for the ephemeral OS disk. Microsoft Learn

Applicability

Use this check during an Azure VM or scale-set deployment when the requested ephemeral OS disk placement is unavailable in the portal.

DSE recommendation

DSE recommends recording the selected image, VM size, and intended placement before troubleshooting the disabled control. Compare the image’s requirements with the selected size rather than repeatedly resubmitting the same deployment. Ask the workload owner to approve any change in size or placement and to document the intended operating model for the machine. Keep this eligibility review separate from a decision to use full caching.

Verification

After revising the approved selection, verify that the intended option is available and that the final deployment request expresses the chosen placement. Inspect the resulting VM or scale-set configuration and compare it with the recorded request. Retain a failed validation result if the option remains unavailable, and investigate the remaining eligibility issue before accepting the deployment.

Official references

• Microsoft: Deploy Ephemeral OS disks – Azure Virtual Machines | Microsoft Learn