# Ultra Disk Compatibility Enabled Without an Attached Ultra Disk Canonical: https://www.pointfive.co/efficiency-hub/inefficiencies/ultra-disk-compatibility-enabled-without-an-attached-ultra-disk To attach an Ultra Disk, a VM must first have Ultra Disk compatibility enabled, which allocates dedicated bandwidth between the VM and the block... By: PointFive Updated: 2026-09-28 [Cloud Efficiency Hub](https://www.pointfive.co/efficiency-hub) The short version To attach an Ultra Disk, a VM must first have Ultra Disk compatibility enabled, which allocates dedicated bandwidth between the VM and the block storage scale unit. PointFive Research Cloud cost research at PointFive Azure service [Azure Managed Disks](https://www.pointfive.co/efficiency-hub/cloud-services/azure-managed-disks) Category [Storage](https://www.pointfive.co/efficiency-hub/service-category/storage) Reference CER-0429 Type Idle or Unused Resource ## Explanation Why the waste happens and who it affects. Azure charges a reservation fee for this capability whenever it is enabled on a VM that has no Ultra Disk attached. The fee is charged per vCPU provisioned on the VM, so it grows with VM size. The situation arises when an Ultra Disk is detached or migrated to Premium SSD v2 but the VM keeps the compatibility flag, when templates or images enable the flag for VMs that never receive an Ultra Disk, or when a planned Ultra Disk is never created. The charge appears against the VM's vCPUs rather than as a disk, so reviews that look for unattached disks do not find it. ## Billing model The pricing dimensions that drive this cost. Ultra Disk compatibility is billed differently depending on whether an Ultra Disk is attached. Ultra Disk VM reservation fee Charged per vCPU provisioned on the VM when Ultra Disk compatibility is enabled and no Ultra Disk is attached Constrained-core sizes For constrained vCPU sizes the fee is based on the full vCPU count, for example 32 vCPUs for Standard\_E32-8s\_v3 Attached Ultra Disk Once an Ultra Disk is attached the reservation fee no longer applies, and the disk is billed for provisioned capacity, IOPS and throughput ## How to detect 4 checks to find it in your estate. - Query Azure Resource Graph for Microsoft.Compute/virtualMachines where properties.additionalCapabilities.ultraSSDEnabled is true, and check whether any entry in storageProfile.dataDisks has managedDisk.storageAccountType UltraSSD\_LRS; VMs with the flag and no Ultra Disk pay the reservation fee - For a single VM, run az vm show with --query "{ultraSSDEnabled:additionalCapabilities.ultraSSDEnabled,dataDisks:storageProfile.dataDisks\[\].name}" and confirm the attached disks' SKUs - In Cost Management, look for the Ultra Disk reservation (provisioned vCPU) charge on subscriptions or resource groups and map it to VMs that have no Ultra Disks - Review VM templates, images and landing zone modules that set ultraSSDEnabled to true by default ## How to fix 3 ways to remove the waste. - Deallocate the VM, set Enable Ultra Disk compatibility to No under Disks \> Additional settings (or run az vm update with --ultra-ssd-enabled false), then start the VM again; the setting can only be changed while the VM is deallocated, so plan it for a maintenance window - Remove the ultraSSDEnabled setting from templates and scale set models for workloads that will not use Ultra Disks - Keep the flag only on VMs that will attach an Ultra Disk soon, and re-check after any Ultra Disk is detached or migrated to Premium SSD v2 ## Documentation Vendor references for pricing and configuration. - [Select a disk type for Azure IaaS VMs - managed disks learn.microsoft.com](https://learn.microsoft.com/en-us/azure/virtual-machines/disks-types) - [Configure Ultra Disks for Azure virtual machines learn.microsoft.com](https://learn.microsoft.com/en-us/azure/virtual-machines/disks-enable-ultra-ssd) - [az vm learn.microsoft.com](https://learn.microsoft.com/en-us/cli/azure/vm) - [Pricing - Managed Disks azure.microsoft.com](https://azure.microsoft.com/en-us/pricing/details/managed-disks/) ## Related inefficiencies [Browse the library](https://www.pointfive.co/efficiency-hub) - Azure Managed Disks CER-0074 ### [Managed Disk Attached to a Stopped VM](https://www.pointfive.co/efficiency-hub/inefficiencies/managed-disk-attached-to-a-stopped-vm) Disks attached to VMs that have been stopped for an extended period, particularly when showing no read or write activity, may indicate abandoned infrastructure or obsolete resources. Retaining these disks without validation leads to... Storage - Azure Managed Disks CER-0073 ### [Managed Disk Attached to a Deallocated VM](https://www.pointfive.co/efficiency-hub/inefficiencies/managed-disk-attached-to-a-deallocated-vm) A VM is deallocated but its attached managed disks are still active and incurring storage charges. While compute billing stops for deallocated VMs, the disks remain provisioned and billable. These disks often persist unintentionally after... Storage - Azure Managed Disks CER-0039 ### [Inactive and Detached Managed Disk](https://www.pointfive.co/efficiency-hub/inefficiencies/inactive-and-detached-managed-disk) Managed Disks frequently remain detached after Azure virtual machines are deleted, reimaged, or reconfigured. Some may be intentionally retained for reattachment, backup, or migration purposes, but many persist unintentionally due to the... Storage --- Source: the public page above. 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