Bad Windows network performance - how to improve?

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CPO_Siemens

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Proxmox Subscriber
Aug 4, 2026
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We migrated some Windows 11 VMs from vSphere to Proxmox and are experiencing network bottlenecks.
I compared two similar VMs (one on vSphere with vmxnet3, one on Proxmox with virtio) and did some iperf3 runs which showed, that the vSphere NIC saturates the 10G connection that the host has to the test server while the Proxmox VM barely reaches 6G outbound and max. 2G inbound while the VM-bridge is attached to a 2x100G bond (which as it's own problems but does way more than 6G).

I also tried enabling multiqueue (set to 8 to match the 8 cores of the VM) and compared different virtual NICs (vmxnet3 was way worse than virtio on Proxmox, e1000 slightly worse as well).
Virtio-Win drivers are also up to date (0.1.302 as of writing this, first used 0.1.285 - no difference).

Any ideas?
 
Didn't know that - tested it.
For outwards traffic this made a tremendous difference. Outbound with 4 threads about 22-30G, inbound with 4-6 threads about 3-6G.
The higher numbers are with multiqueue enabled (set to 4, if I actually use the same number as vCores the VM becomes more or less unresponsive during the transfer).
That is a lot better - especially outbound for some reason.
Up to 6G is also still less than with single threaded iperf3 on vSphere though. Is there any way to meaningfully improve the singlethreaded performance as well?
Not all SMB connections are multi threaded (I think they're single threaded by default) and SMB is our main use case here.
 
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vSphere VMs are on Xeon 6242Rs, Proxmox on Xeon 6354s so slightly newer gen on Proxmox (according to Passmark both should have similar single threaded performance with the Proxmox's CPU slightly better on multithreaded tasks).
 
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