[Feature Request] Support Aligned Zonal Fault Domains for VMSS Flex #32693
Description
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