Windows VMs on Proxmox and KVM: Drivers, TPM, Licensing and Performance

Proxmox VE runs Windows inside KVM virtual machines, with QEMU emulating the hardware. Windows ships with drivers for emulated SATA disks and Intel E1000 network cards, which work but are slow. The fast path is paravirtualized VirtIO hardware, and that needs drivers Windows does not include. Most problems people report with Windows guests trace back to one of the settings below.

The drivers come from the open source virtio-win project and are signed by Red Hat. As of October 2026 the Proxmox wiki still recommends version 0.1.271 for production and lists 0.1.302 as under test, after storage problems in 0.1.285 on busy Windows Server 2025 guests. Roll new driver versions out to a few VMs first. Proxmox notes that write back cache is faster for Windows disks while the default no cache setting is safer.

This is the decision most teams face once VMware renewals get expensive. Hyper-V is part of Windows Server, so an organisation that already licenses Datacenter on every host gets the hypervisor, failover clustering and Windows-native tooling in one stack. Proxmox VE is free and open source, runs Linux containers next to VMs, and charges only for optional support subscriptions.

Source: VM Platform Ledger 2026, with full scorecards for Microsoft Hyper-V and Proxmox VE. Hyper-V scores higher on raw capability. Proxmox VE scores higher on the overall index, which also weighs credibility, buyer risk and lock-in.

Our verdict: choose Hyper-V when nearly every guest is Windows, the team thinks in PowerShell and Failover Cluster Manager, and Datacenter licences are already paid for. Choose Proxmox VE when the estate mixes Linux and Windows, when budget matters more than Microsoft integration, or when you want ZFS, Ceph and Proxmox Backup Server in one product. The side by side detail is in Hyper-V vs Proxmox and VMware vs Hyper-V, and the Hypervisor Advisor ranks platforms for your own workload mix.

Moving Windows to Proxmox or plain KVM does not change what you owe Microsoft. Windows Server 2025 is licensed by physical core, with a minimum of 8 core licences per processor and 16 per server. Standard edition covers two operating system environments per fully licensed server, and Datacenter covers any number. A Proxmox host running more than a handful of Windows guests usually comes out cheaper on Datacenter. Licensing per virtual machine is also possible, but only with subscription licences or Software Assurance.

Activation is the other surprise. Windows ties activation to hardware identifiers, so a guest converted from VMware may ask to be activated again once it sees new virtual hardware. Plan for that in the migration window, and keep your volume licence or KMS details at hand.

Windows 11 requires a TPM and UEFI firmware. On Proxmox VE you add a TPM State disk with version 2.0 and an EFI disk on OVMF. Both can be removed later but not changed once created. Proxmox is open about the limit: an emulated TPM stores its secrets on an ordinary volume, so it satisfies Windows without adding the protection of a physical chip. Our TPM storage on Proxmox guide covers where that state lives and how it behaves during backup and migration.

Secure Boot needs attention in 2026. The original 2011 Microsoft certificates expire in June 2026, and a VM whose EFI disk holds only those certificates will refuse bootloaders signed with the 2023 replacements. New EFI disks made with pve-edk2-firmware 4.2025.05-1 or later carry both sets. Older VMs need the Enroll Updated Certificates disk action or qm enroll-efi-keys while shut down. Suspend BitLocker first, or the guest will ask for its recovery key on the next boot.

Slow Windows guests are the most common complaint in this topic, and the CPU type setting is the first thing to check. The host type passes every host CPU flag to the guest. That sounds fastest, yet several reports on this site show Windows enabling heavier speculative execution mitigations under host, with an emulated model such as x86-64-v2-AES or x86-64-v3 running the same workload much faster. Host also blocks live migration between nodes with different CPUs.

Our verdict: keep the default or pick the newest generic model every node supports, measure, and switch to host only for a concrete reason. WSL and other nested virtualization inside Windows is the usual one. After the CPU, check the disk bus, the driver version and the Windows power plan. QEMU itself is rarely the bottleneck.

Migration from VMware brings its own boot problem. The import wizard in Proxmox VE 8 and later brings Windows disks across on SATA or IDE because those work without extra drivers. Install the VirtIO drivers while the guest runs on SATA, then move the boot disk to VirtIO SCSI. Skipping that order produces the INACCESSIBLE_BOOT_DEVICE stop error.

Passing a GPU to a Windows VM works for CAD, gaming and VDI. The host needs IOMMU support (Intel VT-d or AMD-Vi) enabled in firmware, and the GPU needs its own IOMMU group. Use OVMF when the card's firmware supports UEFI. Two limits to plan around: a VM with a passed-through device cannot be live migrated, and a GPU given to a VM is not available to containers on the same host at the same time.

For backup, enable the guest agent. Proxmox then freezes the guest file system before a backup or snapshot, which on Windows runs through the Volume Shadow Copy Service, so databases and file servers come back consistent. Proxmox Backup Server adds deduplicated incremental backups and verification jobs; the Proxmox backup guide compares it with commercial tools.

Every post below deals with Windows guests on Proxmox, KVM or Hyper-V. Each is grouped by the decision or problem it helps with.