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VMware ESXi and vSphere: vmNIC speeds are limited by your CPU and RAM speeds, not by the vNIC drivers

Posted by jpluimers on 2022/01/11

Still a lot of people think that network speed depends on the vNIC driver and vNIC speed settings.

This is not true: it mainly depends on CPU and RAM speeds as that is where the bottleneck of virtual network processing is.

See:

  • [Wayback] VMXNET3 = 10GbE ? – Hypervisor.fr
  • [Wayback] Debunking the VM Link Speed Myth! – vswitchzero

    10Gbps from a 10Mbps NIC? Why not? Debunking the VM link speed myth once and for all!

    And again, we see  the same pattern. Link speed – even from an adapter type that never supported 10Gbps – has no bearing at all on actual throughput and performance.

    Thankfully, even standard vSwitches support traffic shaping, where you can limit throughput. If you are trying to accomplish this, the traffic shaping feature is a fully functional way to achieve this.

  • [Wayback] virtual_networking_concepts.pdf

    Note: The speed and duplex settings found in physical networking are not relevant in the virtual network, because all the data transfer takes place in the host system’s RAM, nearly instantaneously and without the possibility of collisions or other signaling-related errors.

    vSwitch and vNIC speeds mainly depend on CPU and RAM speeds.

    vSwitch and vNIC speeds mainly depend on CPU and RAM speeds.

–jeroen

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