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VMXNET3 Virtual Adapter Notes

A new vSphere feature is the VMXNET3 network interface that is available to assign to a guest VM. This is one of four options available to virtual machines at version 7 (the other three being E1000, flexible and VMXNET2 enhanced).

There are a couple of key notes to using the VMXNET3 driver. The most obvious is that the guest will appear to be using a 10 Gb/s interface. While the underlying media may not actually be 10 Gb/s, the operating system will perceive it to be. This can assist in VM-to-VM traffic on the same host and port group, and this uses CPU cycles for the local traffic in lieu of the physical Ethernet media in most situations (as does VMXNET2). What it doesn't mean is that it is 10x faster than a 1 Gb/s connection. The VMware VMXNET3 whitepaper shows the gain in performance for a test situation, available in this PDF from VMware.

It's unfortunate that this driver is not the default one for a new virtual machine. There are a few reasons for this, primarily the fault tolerant (FT) virtual machine is not supported with the VMXNET3 driver, nor is it able to be used with paravirtualized SCSI drivers (PVSCSI). Check Scott Lowe's information on this topic.

Windows Server 2008 and Linux virtual machines will benefit most from using VMXNET3 due to added support of key features such as receive-side scaling (RSS). There new features with IPv6 offloading, should you be using it. There are larger transmit and receive buffer sizes with VMXNET3, which can accommodate burst-frequent and high-throughput guest VMs.

I'm going to configure my VMs for the VMXNET3 virtual network driver. I don't have any FT-required systems, nor do I use the PVSCSI drivers.

Do you see yourself using VMXNET3? Share your comments here.

Posted by Rick Vanover on 02/16/2010 at 12:47 PM


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