I have been working with vSphere and VI for a long time now, and have spent the last six and a half years at VMware in the support organization. As you can imagine, I’ve encountered a great number of misconceptions from our customers but one that continually comes up is around VM virtual NIC link speed.
Every so often, I’ll hear statements like “I need 10Gbps networking from this VM, so I have no choice but to use the VMXNET3 adapter”, “I reduced the NIC link speed to throttle network traffic” and even “No wonder my VM is acting up, it’s got a 10Mbps vNIC!”
I think that VMware did a pretty good job documenting the role varying vNIC types and link speed had back in the VI 3.x and vSphere 4.0 era – back when virtualization was still a new concept to many. Today, I don’t think it’s discussed very much. People generally use the VMXNET3 adapter, see that it connects at 10Gbps and never look back. Not that the simplicity is a bad thing, but I think it’s valuable to understand how virtual networking functions in the background.
Today, I hope to debunk the VM link speed myth once and for all. Not with quoted statements from documentation, but through actual performance testing.