[Feature Request] Support Aligned Zonal Fault Domains for VMSS Flex

[fitzgeraldsteele]

Service Team Request

API Spec: Azure/azure-rest-api-specs#39109
Feature Description: Aligned Zonal Fault Domains for VMSS Flex - enables 1:1 mapping between compute fault domains and storage fault partitions within a single Availability Zone
Target GA Date: 2026-06-01

---

Preview Requirements

⚠️ Feature Flag Required During Preview
Register the following AFEC on your subscription:
\\�ash
az feature register --namespace Microsoft.Compute --name ZonalAlignedMultipleFDs
az provider register --namespace Microsoft.Compute
\\

---

Requested Commands

New Parameters for Existing Commands

Command	Parameter	Type	Required	Description
\�z vmss create\	--zonal-fault-domain-align-mode\	string	No	Alignment mode: \Aligned, \Unaligned, \BestEffortAligned\
\�z vmss create\	--os-disk-storage-fd-alignment\	string	No	OS disk alignment override: \Aligned, \Unaligned, \BestEffortAligned\
\�z vmss create\	--data-disk-storage-fd-alignment\	string	No	Data disk alignment override: \Aligned, \Unaligned, \BestEffortAligned\

No New Commands Required

Updates leverage generic --set\ for \�z vmss update.

---

Example Usage

\\�ash

Create VMSS with full alignment

az vmss create \
--name myVmss \
--resource-group myRg \
--location eastus2 \
--zones 1 \
--orchestration-mode Flexible \
--platform-fault-domain-count 3 \
--zonal-fault-domain-align-mode Aligned \
--image Ubuntu2204 \
--vm-sku Standard_D4s_v5 \
--instance-count 3

Create VMSS with best effort alignment

az vmss create \
--name myVmss \
--resource-group myRg \
--location eastus2 \
--zones 1 \
--orchestration-mode Flexible \
--platform-fault-domain-count 3 \
--zonal-fault-domain-align-mode BestEffortAligned \
--os-disk-storage-fd-alignment BestEffortAligned \
--image Ubuntu2204 \
--vm-sku Standard_D4s_v5

Update existing VMSS (using generic --set)

az vmss update \
--name myVmss \
--resource-group myRg \
--set zonalPlatformFaultDomainAlignMode=BestEffortAligned

Query disk alignment status

az disk show \
--name myDisk \
--resource-group myRg \
--query "{alignmentState: storageAlignmentStatus}"
\\

---

API Properties

Model	Property	Type	Description
\VirtualMachineScaleSet.properties\	\zonalPlatformFaultDomainAlignMode\	Enum	Scale set level alignment mode
\VirtualMachineScaleSetOSDisk\	\storageFaultDomainAlignment\	Enum	Per-disk alignment override
\VirtualMachineScaleSetDataDisk\	\storageFaultDomainAlignment\	Enum	Per-disk alignment override
\DiskInstanceView\ (read-only)	\storageAlignmentStatus\	Enum	Current alignment state (Aligned, Unaligned)

---

Dependencies

• Requires swagger PR: Add BestEffortAligned and PerDiskAlignment azure-rest-api-specs#39109
• Minimum API version: \2025-04-01\
• Related to: \�z vmss create, \�z vmss update, \�z disk show\
• Orchestration mode: Flexible only

---

Contact

• PM: Jerry Steele (fisteele@microsoft.com)
• Engineering: Alex Roth (alroth@microsoft.com)
• Service Team: Azure Compute VM Team

[yonzhan]

Thank you for opening this issue, we will look into it.

[github-actions]

Here are some similar issues that might help you. Please check if they can solve your problem.

• Assign Fault Domain during VM Create #16346

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[yanzhudd]

May I confirm whether the Swagger is public? Azure CLI can only develop the feature if the Swagger is publicly available

[fitzgeraldsteele]

hi @yanzhudd. This will be available in the 2025-11-01 CRP API version which is currently working its way through approval, though not public yet. I put a link to the PR for this change above. The branch for the 2025-11-01 api version is here: https://github.com/Azure/azure-rest-api-specs/tree/cplat-2025-11-01