Network performance with VMXNET3 compared to E1000E and E1000. This article explains the difference between the virtual network adapters and part 2 will demonstrate how much network performance could be gained by selecting the paravirtualized adapter.
The VMware administrator has several different virtual network adapters available to attach to the virtual machines. The virtual adapters belong to either of two groups:
These are virtual hardware who emulates real existing physical network adapters. (Note that the physical network cards in the physical ESXi host is totally unrelated.) The VMkernel will present something that to the guest operating system will look exactly as some specific real world hardware and the guest could detect them through plug and play and use a native device driver.
Examples for the emulated devices are:
E1000 – which will emulate a 1 Gbit Intel 82545EM card, and is available for most operating systems since the generation of Windows Server 2003. This card is the default when creating almost all virtual machines and is by that widely used.
E1000E – emulates a newer real network adapter, the 1 Gbit Intel 82574, and is available for Windows 2012 and later. The E1000E needs VM hardware version 8 or later.
Above in Windows 2008 R2 with an emulated E1000 adapter the native guest operating system device driver is in use.
The positive side of the emulated network adapters are that they work “out of the box” and need no external code from VMware. It could be used to even (if needed) install the guest operating system by PXE since the E1000 device is available already from the BIOS start up.
The negative side is when using the default emulated adapters extra work is needed for every frame being sent or received from the guest operating system (which could be many thousands each second).
The VMkernel has to in “real time” emulate the exact behavior of the specific Intel 82545EM or 82574 cards, which will cost time and CPU cycles.
The other type of virtual network adapters are the “paravirtualized”. The most recent one is called VMXNET3.
The paravirtualized network card does not exist as a physical NIC, but is a device “made up” entirely by VMware. For the guest operating system this will mean that it typically during the OS installation phase only senses that an unknown device is located in a PCI slot on the (virtual) motherboard, but it has no driver to actually use it.
(Note: some Linux distributions do even have the VMXNET3 driver pre-installed.)
For Windows Server, when a device driver is supplied, typically through the installation of VMware Tools, the guest operating system will perceive this as a real NIC from some network card manufacturer called “VMware” and use it as an ordinary network adapter. It has no reason to believe anything else than this is a NIC just as any other NIC around.
To the guest operating system the VMXNET3 card looks like a 10 Gbit physical device.
Note: there are also two obsolete paravirtualized adapters called VMXNET and VMXNET2 (sometimes the “Enhanced VMXNET”), however as long as the virtual machine has at least hardware version 7 only the VMXNET3 adapter should be used.
Since VMware with the VMXNET3 card owns much more of the network components even inside the VM there are many performance enhancements that could done. With the emulated E1000/E1000E the kernel has to mimic the exact behavior of existing adapters to the guest but with the VMXNET3 it could create a “perfect” virtual adapter optimized to be used in a virtual environment.
In part 2 of this article we will see how really large the performance difference actually is.