Poor user experience with Windows Server 2025 on Proxmox

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qemu

New Member
Mar 27, 2026
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Hi everyone,


I’d like to share an issue we’re experiencing and see if anyone has encountered something similar or can provide some insight.


We have been testing Windows Server 2025 on Proxmox VE 8.4 (QEMU 9) as well as Proxmox VE 9.1 (QEMU 10). We tried different CPU configurations and resource allocations, but in all cases the user experience is noticeably worse compared to Windows Server 2022 and earlier versions.


Observed issue​


The main problem appears when navigating folders:


  • File Explorer is not responsive instantly
  • It briefly shows a blank (white) window
  • Then the folder contents load afterward

This behavior did not occur with previous Windows Server versions under similar conditions.


Environment details​


  • Host:
    • CPU: Intel Xeon E5-2630 v4
    • RAM: 128 GB
  • Virtual Machine:
    • 8 vCPU
    • 32 GB RAM
    • Disk in qcow2 format
  • Configuration:
    • Following both Proxmox and Microsoft best practices
    • VirtIO drivers version 271 installed

Additional testing​


We tested the same setup (Windows Server 2025) on a Nutanix environment using the same hardware (same Xeon CPU), and the experience is perfectly smooth. The issue only occurs on Proxmox.


Questions​


We are considering several possible causes:


  • Could this be due to an outdated CPU?
  • Are we missing any important Proxmox tuning or configuration?
  • Could it be a lack of optimization between Proxmox and Windows Server 2025?
  • Has anything changed in File Explorer behavior in this version?

Any feedback, similar experiences, or suggestions would be greatly appreciated.


Thanks in advance!
 
As always, it primarily depends on the underlying hardware (CPU/BIOS patch level).
The Intel Xeon E5-2630 v4 is 10 years old (and as new not very fast...) :rolleyes::oops:
 
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Per Microsoft's own website, that processor is not (officially) supported. Only 2nd gen Xeon Scalable and up for Windows 2025.

However, Nutanix is also QEMU, but will attempt to pass through as much of the CPU as possible. So something like x86-v2 is ultimately too restrictive, I would set it to host to begin with.

Given the errors are seemingly UI-based or potentially file-based, what is the difference between your Nutanix and Proxmox setup as for storage? Proxmox by default sets the storage to no cache, Windows always operates in write-back unsafe for NTFS, but write-back (safe) option is likely the best for safety.
 
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Make sure that your CPU and NUMA configuration are set correctly. This is something I had to learn coming from VMware. Proxmox does exactly what you configure VM vCPUs to be. If things are mis-configured, the VM will run poorly and be sluggish.

Here is the rule of thumb I use (this will depend on your host CPUs):

1 socket with multiple cores, (up to 12 or so) with NUMA UN-checked
If your host has more than one socket, check NUMA box and assign multiple sockets and cores.

**Here is the key: Your host must have the physical sockets and the CPU should have the number of physical cores your assigning in the VM configuration**
 
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How is cross-socket memory access and topology mismatches not an issue?

Compared to VMware that just "fixes" incorrect vCPU settings, Promox will do what you tell it, without guardrails.
 
We have tested with the latest VirtIO drivers and the disk in RAW format, also configuring the system for maximum performance, but for example, on the desktop, when opening the context menu, there is noticeable lag; it is not instantaneous like in Windows Server 2022 or earlier.

Windows Server 2025 feels less optimized. We do not have the possibility to test it on new hardware, only to try to fine-tune it as much as possible.
 
I’m still running tests, and on CPUs of the same generation—or even older ones—running Nutanix or VMware, it works correctly.


I suspect it’s a lack of optimization, but not related to CPU or RAM; I’d say it might be GPU-related.


I’ve checked that even with VirtIO-GPU enabled, Windows Server 2025 was using the basic drivers. I disabled them, but since I only access the machine via RDP, I suspect it’s not properly picking up the correct driver. I’m still experiencing latency when opening the context menu from the desktop or when navigating between directories. It doesn’t switch instantly and display the data; instead, there’s a slight delay where the Explorer window appears blank for a fraction of a second before rendering.
 
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