By David Smith, Founder and CEO, Atlas AVD, , updated
Yes, with conditions: Microsoft supports ephemeral OS disks for Azure Virtual Desktop session hosts only in pooled host pools that use a session host configuration. These are the automated host pools that come with enhanced host pool management, which Microsoft announced as generally available in July 2026. Personal host pools, and standard host pools whose session hosts you deploy and register yourself, aren't supported. That's why Microsoft's general AVD prerequisites still list ephemeral OS disks among the things not supported for session hosts. Ephemeral hosts can't be deallocated, so a supported pool scales by creating and deleting hosts instead of starting and stopping them.
The short version: An ephemeral OS disk lives on the VM's local storage instead of in Azure Storage, so it has lower latency and resets quickly. Use it in a pooled host pool with a session host configuration, with dynamic autoscaling set to create and delete hosts. Don't use it in a personal pool or a standard host pool: that's outside what Microsoft supports. And remember what you give up anywhere: no deallocation, no snapshots, image capture, Azure Backup or Site Recovery, and the OS disk is wiped whenever Azure redeploys, resizes or heals the VM.
Everything below is from Microsoft Learn and the Azure Virtual Desktop blog as of November 2026, with each source linked. Microsoft's pages don't all agree yet (see below), so check them before you design a pool.
Where Microsoft supports ephemeral OS disks on AVD
From Ephemeral OS disks on Azure Virtual Desktop: "Ephemeral OS disks in Azure Virtual Desktop are supported only in pooled host pools configured with session host configuration."
| Host pool | Ephemeral OS disks supported? |
|---|---|
| Pooled, with a session host configuration (automated host pool) | Yes |
| Pooled, standard management (you deploy and register the VMs) | No |
| Personal | No |
| Azure Government | No, according to the Learn page's preview notes |
Microsoft's pages disagree on the details. The general availability announcement (July 2026) includes ephemeral OS disks in enhanced host pool management. The Learn page, last updated September 2026, still carries preview limits:
- Only Standard SSD is supported as the OS disk type (the base disk).
- Ephemeral OS disks "aren't supported with NVMe and premium SSD".
- They're "not supported in Azure Government".
Meanwhile the AVD prerequisites still list "Ephemeral OS disks for Azure VMs" among the items that "aren't supported for session hosts", with no exception for automated host pools. Read that as applying to standard host pools. The same page notes that West US 3 isn't supported for automated host pools.
What an ephemeral OS disk is
A normal (persistent) OS disk is a managed disk in Azure Storage. An ephemeral OS disk is created on the VM's local storage, "not saved to the remote Azure Storage", which gives lower read and write latency and a faster reimage (ephemeral OS disks). Microsoft describes them as "ideal for stateless workloads", which is what a pooled AVD host with FSLogix profiles is.
Where it's placed. For AVD, Microsoft documents two placements: the VM's OS cache or its temp disk. The OS image must fit. The Windows 11 Enterprise multi-session image is 127 GiB, so you need a size whose cache or temp disk is at least that big; Microsoft's example is Standard_D8s_v3, whose 200 GiB temp disk leaves about 73 GiB after the OS disk.
Cost. There's no charge for the ephemeral OS disk itself, but if you choose a Standard SSD or Premium SSD base disk, "you pay the applicable base disk charges". On AVD during the preview limits above, the base disk is Standard SSD.
Ephemeral vs persistent OS disks
From Microsoft's comparison table:
| Persistent OS disk | Ephemeral OS disk | |
|---|---|---|
| Supported for AVD session hosts | Yes | Pooled host pools with a session host configuration only |
| Stop or deallocate the VM | Yes | Not supported |
| Resize to a new VM size | OS disk data is preserved | OS disk is wiped and reprovisioned |
| Redeploy | OS disk data is preserved | OS disk is wiped and reprovisioned |
| Service healing after a host failure | OS disk data is preserved | OS disk data isn't preserved |
| Live migration | OS disk data is preserved | OS disk data is preserved |
| Resize the OS disk | At creation, or after deallocating | At creation only |
| Windows page file | On the temp disk | On the OS disk |
| Snapshots, image capture, Azure Backup, Site Recovery | Supported | Not supported |
| Azure Disk Encryption | Supported | Not supported (encryption at host works) |
How scaling works with ephemeral hosts
AVD usually saves money by deallocating idle hosts, with scaling plans and Start VM on Connect. Ephemeral hosts can't be deallocated, so Microsoft recommends dynamic autoscaling with Minimum percentage of active hosts (%) set to 100% in every phase. The scaling plan then creates hosts when demand rises and deletes them when it falls, instead of starting and stopping them.
Deleting an idle host stops its compute charges just as deallocating does. The trade-off is time: creating and registering a new host takes longer than starting a stopped one, so set the ramp-up phase early enough that hosts are ready before the morning sign-ins.
To move an existing automated host pool to ephemeral OS disks, edit its session host configuration and schedule a session host update, which redeploys the hosts with the new settings.
When ephemeral OS disks make sense, and when to skip them
Good fit:
- Pooled, multi-session hosts with profiles in FSLogix and no data on the OS disk.
- Pools you rebuild often from a golden image, where a fast, clean reset is the point.
- Pools where OS disk latency matters, since reads and writes stay on the VM's local storage.
Skip them when:
- The pool is personal, or uses standard management. That's outside Microsoft's support.
- You rely on Start VM on Connect to keep hosts off until someone connects.
- You need snapshots, image capture from a host, Azure Backup or Site Recovery.
- You deploy in Azure Government, or need Premium SSD or NVMe placement, while the preview limits stand.
- Something on the host depends on keys sealed by the vTPM. For Trusted Launch VMs, Microsoft warns that such keys "might not be saved" and "could be lost during actions such as reimaging or service healing events".
For standard host pools: what to do instead
If your pool isn't an automated host pool, you can still get most of the saving on a supported configuration.
Pick the cheaper disk tier for pooled hosts. With profiles in FSLogix, many pooled hosts run well on Standard SSD rather than Premium SSD. Test logon times on a pilot host first. Our AVD sizing guide covers OS disk size and type.
Deallocate idle hosts. Use scaling plans or your management platform's autoscale, plus Start VM on Connect. Our guide to controlling AVD spend shows the order to turn these on.
Move switched-off hosts to a cheaper disk. A deallocated host still pays for its managed OS disk. You can change a deallocated VM's disk to Standard HDD and back to SSD before it starts, which cuts the disk cost for the hours it's off without slowing it down while it runs.
Replace hosts instead of patching them. Rebuilding hosts from a golden image gives you the same clean reset. See golden image management and replace hosts vs staged rings.
How Atlas AVD handles ephemeral OS disks
Atlas AVD deploys and registers session hosts itself, in standard host pools, rather than through an AVD session host configuration. So the support Microsoft gives ephemeral OS disks in automated host pools doesn't extend to a pool Atlas builds on them.
Atlas still lets you choose an ephemeral OS disk when deploying a pool, but only on VM sizes that support one, and it warns you when the OS disk won't fit the size's cache, temp or NVMe storage. Once the hosts exist, autoscale never stops them (it still starts hosts when demand rises), the power control shows Delete instead of Stop, and Smart Disk Tiering leaves them alone.
For production pools managed by Atlas, we recommend managed disks with Smart Disk Tiering: it moves the OS disk of a deallocated, empty host down to Standard HDD and back to the pool's performance tier before autoscale starts it again. The Smart Disk Tiering guide explains the modes.
FAQ
Are ephemeral OS disks supported for Azure Virtual Desktop?
Yes, in pooled host pools that use a session host configuration (automated host pools). They aren't supported in personal host pools or in standard host pools, as of November 2026.
Why do Microsoft's AVD prerequisites say ephemeral OS disks aren't supported?
The prerequisites list describes session hosts in general and doesn't mention the exception for automated host pools. Microsoft's dedicated page on ephemeral OS disks for AVD is the one that sets the exception.
Do ephemeral OS disks save money on AVD?
They remove the OS disk storage charge, apart from any SSD base disk. In an automated host pool, the scaling plan deletes idle hosts, which stops their compute charges. In a standard pool, they can't be deallocated, so they keep paying for compute unless you delete them.
Can I stop or deallocate a VM with an ephemeral OS disk?
No. You can only restart, reimage or delete it.
What happens to an ephemeral OS disk when the VM is resized or redeployed?
The data on the OS disk is deleted and the OS is reprovisioned from the image. The same happens if Azure heals the VM after a host failure. Live migration keeps the data.
Can I convert an existing session host to an ephemeral OS disk?
Not in place. In an automated host pool, edit the session host configuration and schedule a session host update, which redeploys the hosts. Otherwise, deploy new hosts and retire the old ones.
Last updated 10 November 2026. Microsoft details are drawn from Microsoft Learn and the Azure Virtual Desktop blog as of November 2026: Ephemeral OS disks on Azure Virtual Desktop, Enhanced host pool management is now generally available, Prerequisites for Azure Virtual Desktop and Ephemeral OS disks for Azure VMs. Microsoft's pages don't yet agree on the preview limits, so check them before you design a pool.