VMware Server – Increasing speed of vmnets

Do you expereince slow data trasfers between your guest operating systems? Is data transfer between the host and guest also very slow? Are you getting megabyte trasefer rates even though your network adpaters are of gigabit speeds? Here is the solution.

The slow trasfer rates between VMware guest operating systems could be due to VMware tools not being correctly installed. Please check whether VMware tools service is running correctly in your Guest OS. Other than mouse and SVGA features, this is what VMware tools does to your Guest OS.

It will install the virtual network driver vmxnet instead of the default vlance. Network devices of the host machine communicates to the vlance driver just like the way it does to real hardware hence a lot of hardware overhead comes with this driver(it constantly checks whether the network is plugged etc..). But vmxnet is treated differently and differentiates itself as a virtual driver and hence a lot of unnecessary hardware checks are avoided.

This improves the network performance and gives you gigabit speeds.The following diagram tell you whether it is properly installed.

vmxnet Windows driver

But the more serious problem that most people face is the slow data trasfer between the host and the guest OS. Their complain always goes like this “I have gigabit network adapters for both my host and my guest OS. But why is that I still have only megabyte trasfer rates between host and guest?”.

After a lot of googling and consulting within the community, i am assuming that Vmware server is designed that way so that gigabit data trasfers are not possible(remember there is no thing as free lunch). In Vmware ESX, there is a straighforward option to configure the speed of the network adapter. Even if you set it as ‘automatic’, it would directly allot the speed of the pipe as gigabit if both your host and guest has that capacity.

However, you can always speed the transefer between your host and guest. One way is to turn off the unwanted checks done by your network adapter. If your host is Linux, you may use ethtool and for Windows, you can directly go to the advanced settings of the network adapter and turn OFF settings for TSO(TCP segmentation offload).Look below for the screenshot. What this setting does is to quicken the file transfer between the host and the guest.


Windows network adapter configuration


9 thoughts on “VMware Server – Increasing speed of vmnets”

  1. Thank you soooooo much! You just helped put our Virtual Machine network speeds through the roof!!!

  2. My “VMware Virtual Ethernet Adapter for VMnet” are configured at 100Mbps although my host OS (Windows 2008 32 Bit) has 1.0Gbps. Please tell me how can I set Virtual Adapters to 1.0G.


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