Use Ephemeral OS Disks in Azure

In Azure, you have the option to create Ephemeral OS disks for your machine. This sounds really cool but what is it actually, what pro’s and cons are coming with them, what is the pricing and how do we use them? I will do my best to explain everything in this guide.

Requirements
What are Ephemeral OS Disks?
- Ephemeral OS Disk topology
- Managed OS Disk topology
Pro’s and Cons of Ephemeral OS Disks
Theoretical performance difference
Let’s deploy a virtual machine with Ephemeral OS disk
Testing Ephemeral OS disk performance
Summary
- Sources

📖 Estimated read time: 7 minutes

🔄 Page last updated on: July 23, 2025

Requirements

Around 25 minutes of your time
An Azure subscription (if wanting to deploy)
Basic knowledge of Azure
Basic knowledge of servers and infrastructure

What are Ephemeral OS Disks?

Ephemeral OS Disks are disks in Azure where the data is stored directly on the hypervisor itself, rather than having a managed disk which could be resided at the very other end of a datacenter. Every cable and step between the disk and the virtual machine creates latency which will result in your machine being slower.

Ephemeral OS Disk topology

Now this looks really how it normally should look.

Managed OS Disk topology

Now, let’s take a look at how normal, Managed disks work:

Topologies are simplified for more understanding.

As you can see, they could be stored anywhere in a datacenter or region. It could even be another datacenter. We can’t see this in the portal. We only see that a VM and disk are in a specific region and availability zone, but we don’t have further control.

Configuring Ephemeral OS Disks so mean much less latency and much more performance. Let’s dive into the pro’s and cons before being overjoyed.

Pro’s and Cons of Ephemeral OS Disks

Now let’s outline the pro’s and cons of Ephemeral OS Disks before jumping into the Azure Portal and configuring them:

Pro	Con	Difference with managed disk
Very high disk performance and great user experience	Only support for VM sizes with local storage (includes non-capital “d” in size: D8dv4, E4ds_v6	Managed disks support all VM sizes
No disk costs	Deallocation of VM not possible, VMs must be on 24/7	Deallocation possible, saving money when VMs are shutdown and deallocated
	Data storage is non-persistent, this means when a VM is redeployed or moved to another host, you data will be gone	Managed disks are persistent across a complete region
	No datacenter redundancy, VMs stay in the same datacenter for its lifetime	Datacenter redundancy and region redundancy possible with ZRS and GRS
	Resizing of disk not possible	Resizing possible (only increase)
	Backup, imaging or changing disk after deployment not possible	Backup, imaging and changing disks possible

As you can see, this is exactly why I warned you for the cons, because these cons make it unusable for most workloads. However, there is at least one use-case where I can think of where the pros weigh up to the cons: Azure Virtual Desktop.

Theoretical performance difference

According to the Azure Portal, you have the following performance difference when using Ephemeral OS disks and Managed disks for the same VM size:

When using a E4ds_v6 VM size (and 128GB size disk);

Disk type	IOPS	Throughput (Mbps)
Ephemeral OS disk	18000	238
Managed OS disk	500	100

Let’s deploy a virtual machine with Ephemeral OS disk

To deploy a new virtual machine with a Ephemeral OS disk, follow these steps:

Select a resource group
Give it a name
Disable availability zones (as this is not supported)
Select your image (Windows 11 24H2 Multi-session in my case)

Now we have to select a size, which mus contain a non-capital “d”. This stands for having local NVME storage on the hypervisor which makes it bloody fast. In my case, I selected the vm size: “E4ds_v6”

Now the wizard looks like this:

Proceed by creating your local account and advance to the tab “Disks”.

Here we have to scroll down to the “Advanced” section, expand it and here we have the hided options for having Ephemeral OS disks:

Select the “NVME placement” option and let the option “Use managed disks” checked. This is for additional data disks you link to the virtual machine. The Ephemeral OS disk option requires you to enable it.

Finish the rest of the wizard by selecting your needed options.

Testing Ephemeral OS disk performance

Now that the virtual machine is deployed, we can log into it with Remote Desktop Protocol:

In my test period of about 15 minutes, the VM feels really snappy and fast.

Performance testing method

To further test the speed of the VM storage, I used a tool called Crystal Disk Mark. This is a generic tool which tests the disk speed of any Windows instance (physical or virtual).

Performance testing results

To have a great overview of the speeds, I have created a bar diagram to further display the test results of the different tests, each separated by read and write results:

Conclusion from test results

My conclusion from the test results is that Ephemeral OS disks does provide more speed when doing specific actions, like in the random 4KB tests, where it delivers 3 to 10 times te performance of managed disks. This is where you actually profit from the huge increase in Input Output operations Per Second (IOPS)

The sequential 1MB speeds are quite similar to the normal managed disks, in the read cases even slower. I think this has to do with traffic or bottlenecking. As my research goes, disk speed increases when the size of the VM increases, but I could not go for like D64 VMs due of quota limits.

Both of the test were conducted between 20 minutes of each other.

Raw data

Here is the raw data of the tests. Left is Ephemeral and right is Managed disk results.

Summary

Ephemeral OS Disks ensure the VM is powered by great disk performance. Storage will not longer be a bottleneck when using the VM but it will be mostly CPU. However, it comes at the cost of not being able to perform some basic tasks like shutting down and deallocating the machine. Restarting is possible and these machines have an extra option, called “Reimage”, where they can be built again from a disk/image.

If using VMs with Ephemeral OS disks, use it for cases where data loss is no issue om the OS disk. All other data like data disks, data on storage account for FSLogix or outside of the VM is unharmed.

Sources

Thank you for reading this guide and I hope it was helpful.

End of the page 🎉

You have reached the end of the page. You can select a category, share this post on X, LinkedIn and Reddit or return to the blog posts collection page. Thank you for visiting this post.

If you think something is wrong with this post or you want to know more, you can send me a message to one of my social profiles at: https://justinverstijnen.nl/about/

Go back to Blog

The terms and conditions apply to this post.

Page visitors: No page-counter data available yet.

Published by Justin on July 24, 2025July 24, 2025

Table of Contents

Requirements