Ephemeral Disk Support for NCasT4_v3 sizes series

Jubish Jose 5

I am trying to create a Windows 11 23H2 VM of size Standard_NC8as_T4_v3 with ephemeral disk placed on OS cache. Looking at https://learn.microsoft.com/en-us/azure/virtual-machines/sizes/gpu-accelerated/ncast4v3-series?tabs=sizebasic, it says ephemeral disks are supported.

We need to deploy this VM as a gold image to use on VMware Horizon on Azure Cloud and want 512 GB of disk space considering the number of applications we have. But when choosing ephemeral disk, the disk size defaults to 127 GB.

Is there a way I can create a VM with 512 GB disk with ephemeral option?

Lijitha B 330 Reputation points Microsoft Vendor

2024-09-17T07:42:18.83+00:00

Hi Jubish Jose,

I understand that you are facing an issue with creating a Standard_NC8as_T4_v3 Windows 11 VM including a 512 GB ephemeral disk!

If you choose to deploy ephemeral OS Disk on VM cache or VM temp disk. The image OS disk’s size should be less than or equal to the temp/cache size of the VM size chosen. Size requirements

Ephemeral disks use the VM's temporary storage or cache. This size is fixed for each VM size and can't be increased beyond what the VM type offers
Below You can explore two alternative approaches: Switch to a managed OS disk: You can change from using the unmanaged data disk to using a managed OS disk, which makes it possible to use custom sizing up to 4 TB. For example, you could use this technique to provision a VM with a 512 GB OS disk that meets the needs of your application. Attach a data disk: If you could live with ephemeral OS disk (127GB - for the operating system), then you could attach another data disk of 512 GB to store your apps.

For detailed information please go through the followed links:
Azure managed disks overview
Ephemeral OS disks for Azure VMs

If you have any further queries, do let us know. If it was helpful, please click "Upvote" on this post to let us know.
Jubish Jose 5 Reputation points

2024-09-18T00:43:45.2366667+00:00

Thanks for the response. How can I find the OS cache size of Standard_NC8as_T4_v3? O don't see this in the documentation.

Installing app on the data disk may not be a good idea. We have a lot of heavy apps and we prefer to use the default installation path due to a few dependencies.
Lijitha B 330 Reputation points Microsoft Vendor

2024-09-20T06:58:49.84+00:00

Hi Jubish Jose,
Just checking in to see if you have got a chance to see the comment posted in resolving the issue.If it was helpful, please click "Upvote" on this post to let us know.

1 answer

Lijitha B 330 Reputation points Microsoft Vendor

2024-09-18T07:21:31.28+00:00

Hi Jubish Jose,
Thanks for sharing information.

The maximum size for an ephemeral OS disk on the Standard_NC8as_T4_v3 virtual machine size is 127 GB, as you have observed. This is because the ephemeral OS disk is stored on the VM's cache disk, which has a maximum size of 127 GB for this virtual machine size.

If you need more than 127 GB of disk space for your gold image, you may want to consider using a managed disk instead of an ephemeral disk. Managed disks can be larger than 127 GB and can be used as the OS disk for your virtual machine.

If you have any further queries, do let us know. If it was helpful, please click "Upvote" on this post to let us know.
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Lijitha B 330 Reputation points Microsoft Vendor

2024-09-24T01:36:47.0566667+00:00

Hi Jubish Jose,

Following up to see if the above answer was helpful. If this answers your query, do click Accept Answer and Upvote for was this answer helpful. And, if you have any further query do let us know.
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Ephemeral Disk Support for NCasT4_v3 sizes series

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