Severe I/O performance degradation on Windows VMs (Server 2022) on Proxmox 8/9

[NaderSanders]

Hi everyone,
we are currently facing significant performance issues with Windows guests on both Proxmox VE 8 and 9.

Environment:

• Proxmox VE 8 and 9 (tested on multiple nodes)
• Storage:
  • Local SSD (Software RAID 1)
  • Ceph cluster
• Guest OS:
  • Windows Server 2022

Configuration:
The VM was set up according to the official recommendations:

• VirtIO SCSI controller
• VirtIO drivers installed (latest stable ISO)
• Balloon driver installed
• QEMU Guest Agent installed and running

Problem:
The I/O performance inside the Windows VM initially appears normal, but under load it drops dramatically after a short time.

Symptoms:

• Disk throughput collapses after a few seconds of sustained load
• High latency inside the guest
• System becomes sluggish/unresponsive
• Issue occurs on both local storage (SSD RAID1) and Ceph

What we already tested:

• Different storage backends (local vs. Ceph)
• Reinstalled VirtIO drivers
• Tested with and without Ballooning
• Different disk cache modes (writeback, writethrough, none)
• Different bus types (VirtIO SCSI vs. SATA for comparison)

Observations:

• The issue seems independent of the storage backend
• Linux guests on the same hosts perform normally
• Problem appears specific to Windows guests

Questions:

• Is this a known issue with Proxmox 8/9 and Windows Guests?
• Are there recommended settings for stable I/O performance under load?
• Could this be related to VirtIO drivers or specific kernel/QEMU versions?

Any hints or similar experiences would be appreciated.
Thanks in advance.

 

[spirit]

What is your virtio driver version ? Use 0.1.271 if possible. Previous and more récent have known bugs

 

[SteveITS]

Link to that for posterity: https://pve.proxmox.com/wiki/Windows_VirtIO_Drivers#Known_Issues

 

[jaminmc]

What is your virtio driver version ? Use 0.1.271 if possible. Previous and more récent have known bugs

Link to that for posterity: https://pve.proxmox.com/wiki/Windows_VirtIO_Drivers#Known_Issues

Yes, you’re right! virtio-win-0.1.285 has a significant issue. You can find it here: https://github.com/virtio-win/kvm-guest-drivers-windows/issues/1453.

The issue was resolved in https://github.com/virtio-win/kvm-guest-drivers-windows/pull/1465.

So, newer versions should work well, once they are released. The GitHub site also has pre-releases, but https://fedorapeople.org/groups/vir...ownloads/archive-virtio/virtio-win-0.1.271-1/ is the official recommended version for now.