Resource Allocation failed

Question

Allocation failed. Azure does not have sufficient capacity for the requested VM size in this Central US zone 1.

Answer 1

Hello @Husain Vijapura ,

This is a known and expected behavior in Azure.

It indicates that the required physical hardware for your selected VM size is temporarily unavailable in Central US (Zone 1). Azure VM capacity depends on the availability of physical hardware within each region and availability zone. When a specific zone runs out of capacity for a particular VM SKU, new deployments or allocations for that size cannot be completed.

As you mentioned, this is impacting your business operations since the VM is required for critical workloads. To avoid encountering the same issue in the future, it is recommended to select multiple availability zones during deployment, which helps improve resiliency and increases the likelihood of capacity availability.

Please note that this is a temporary capacity constraint and is not caused by any misconfiguration in your environment.

Answer 2

I am following up on the previously raised support request regarding the VM deployment failure.

We are currently receiving the following error while attempting to deploy/start the VM:

"Allocation failed. Azure does not have sufficient capacity for the requested VM size in Central US zone 1."

This issue is impacting our business operations, as the VM is required to run critical workloads. We are currently unable to proceed due to the capacity limitation in this zone.

Your prompt assistance would be greatly appreciated due to the business impact of this issue.

Best regards, Husain

Answer 3

Hello Husain

I understand how blocking this can be—especially when you need to bring the VM online immediately. The error you’re seeing (Allocation failed / insufficient capacity) happens when Azure is temporarily unable to allocate the requested VM size in the chosen region/Availability Zone due to platform capacity constraints.

This issue is not related to your configuration, but rather a capacity shortage in the underlying Azure infrastructure. This can happen, especially with large or specialized VM sizes, or during peak times.

Please follow these steps:

• If you’re using availability zones, try selecting another zone within the same region. It’s possible that a different zone has available capacity for the VM size you need.
• Resize a VM or add a VM to an existing availability set must be tried at the original cluster that hosts the existing availability set. The requested VM size is supported by the cluster, but the cluster may not currently have sufficient capacity.
• If the VM can be part of a different availability set, create a VM in a different availability set (in the same region). This new VM can then be added to the same virtual network.

Stop (deallocate) all VMs in the same availability set, then start all applicable VMs in batch. To stop: Click Resource groups > Resources > Virtual Machines > Stop. After all, VMs stop, navigate to Home > Virtual machines, add an Availability set filter and then select Group by availability set. Select all applicable VMs and click Start.

This step makes sure that a new allocation attempt is run and that a new cluster can be selected that has sufficient capacity.

For detailed information, please check: https://learn.microsoft.com/en-us/troubleshoot/azure/virtual-machines/windows/allocation-failure

Also we have verified with the engineering team and they have provided the workaround :

Capacity is currently constraint for the SKU and try deploying NDsr_H100_v5-series in the same region.

If the issue persists after trying the above options, we’re happy to help further please add details in the Comment section (VM size/SKU, region, availability zone selection, and whether resizing/zone change is possible), and we will respond promptly.

Thanks,
Manish.

Answer 4

The error indicates an allocation failure because there isn’t enough capacity for the requested VM size in Central US zone 1. This is a platform capacity issue, not a quota or configuration problem.

To increase the chance of a successful deployment, use one or more of these options:

1. Retry the allocation
   • Capacity constraints can be temporary. Try the same deployment again later.
2. Use an alternative VM size
   • Select a different SKU that has capacity in the same region/zone. In the portal, use the alternative size recommendations shown with the error (for example, sizes like Standard_A2_v2, Standard_A2m_v2, or Standard_D2a_v4 as in the example from the guidance) and redeploy or resize the VM.
3. Change zone or region
   • Try deploying the same VM size in a different availability zone within Central US (for example, zone 2 or 3 if available).
   • If zonal deployment is not required, remove the zone constraint so the VM can be allocated anywhere in the region.
   • If the region itself is constrained, deploy the VM in another region that supports the SKU.
4. Reduce constraints (for overconstrained scenarios)
   • If the request also uses constraints such as proximity placement groups, accelerated networking, ephemeral OS disk, or Ultra/PremiumSSDv2 disks, remove or relax these where possible and retry.
5. For existing availability sets or scale sets
   • If resizing or starting VMs in an availability set fails, consider:
     • Resizing to a supported size for that availability set.
     • Stopping (deallocating) all VMs in the availability set and then starting them together so allocation can use all clusters in the region.
   • For Virtual Machine Scale Sets, follow the same allocation guidance as for standalone VMs; if the scale set is pinned to a single cluster, consider a new scale set in the same region with a different size or zone.
6. Plan ahead with capacity reservations
   • For critical workloads that must always start successfully, use On-demand Capacity Reservations to reserve capacity for specific VM sizes in advance.

If none of these options are acceptable for the workload, wait and retry later; capacity in the requested zone may free up over time.

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References:

• Troubleshoot allocation failures when you create or resize VMs in Azure
• Fix an AllocationFailed or ZonalAllocationFailed error when you create, restart, or resize Virtual Machine Scale Sets in Azure
• Troubleshoot the ZonalAllocationFailed, AllocationFailed, or OverconstrainedAllocationRequest error code
• Troubleshoot deployment issues with restarting or resizing an existing Windows VM in Azure
• Troubleshoot allocation failure in Azure Cloud Services (extended support)