Memory Hotplug and Windows 11/Windows Server 2025

[bertram]

When activating memory hotplug on a Windows 2025 VM, Windows setup constantly fails with an error I didn't remember. When doing the same with Windows 11, setup complains about needing at least 4GB of RAM. No matter, how much memory is assigned to the vm.

This is reproducible. Is this a know behaviour?

When enabling memory hotplug after the setup, everything is working fine. Even changing memory size.

This is the config of a non-working vm:

agent: 1
bios: ovmf
boot: order=virtio0;ide1;ide0;net0
cores: 2
cpu: x86-64-v2-AES
description: Windows 11 Evaluation Template
efidisk0: dir-8t-ssd:111/vm-111-disk-0.raw,efitype=4m,pre-enrolled-keys=1,size=528K
hotplug: disk,network,usb,memory,cpu
ide0: local:iso/win11_eval_x64FRE_en-us.iso,media=cdrom,size=6926570K
ide1: dir-ssd:iso/virtio-win-0.1.285.iso,media=cdrom,size=771138K
machine: pc-q35-9.2+pve1
memory: 6144
meta: creation-qemu=9.2.0,ctime=1760102185
name: templ-win11
net0: virtio=BC:24:11:79:0F:63,bridge=vmbr0,firewall=1
numa: 1
onboot: 0
ostype: win11
scsi0: dir-8t-ssd:111/vm-111-disk-1.raw,backup=0,cache=writeback,discard=on,iothread=1,size=52G,ssd=1
scsihw: virtio-scsi-single
smbios1: uuid=a6f8f8b1-3e31-42ba-9c1d-73fe3486db8e
sockets: 1
tags: windows,win11,ansible,template
tpmstate0: dir-8t-ssd:111/vm-111-disk-2.raw,size=4M,version=v2.0

PVE-Version pve-manager/8.4.13/5b08ebc2823dd9cb (running kernel: 6.8.12-15-pve)

 

[MarkusKo]

That's expected, the windows PE image used for the windows installer gui does not include any virtio drivers. For memory hotplugging to work you have to install virtio guest utils after windows is installed.

If you have to install windows more often you could integrate the virtio drivers into the windows installer image. But i'm not sure if memory hotplugging works in the windows setup even if the drivers are included, never tested this myself.

https://learn.microsoft.com/en-us/w...s-to-an-offline-windows-image?view=windows-11