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VMware ESXi - Transmit buffer setting question.

Trusted Contributor

VMware ESXi - Transmit buffer setting question.

Trung had a VMware question:




Just wondering if anyone can confirm if there is a transmit buffer setting for a ESX host for the physical NICs (FlexFabric CNAs).


A customer has received a recommendation from Microsoft for setting transmit buffer for a Mocrosoft Lync Server 2010 VM. My guess is that it has to do with Hyper-V or a VM specific setting as I can’t seem to find any setting for this at the ESX host level.


Any comments appreciated.




From Deepak:




If Physical Nic support this feature and has proper driver which allows us to manipulate this value. Then this option will be available to virtual machines NIC settings too. If physical NIC does not have this feature then you won’t be able to manipulate it for VMs too.




From Jim:




For VMXNET, the default number of receive and transmit buffers is 100 each, with the maximum possible

being 128. For Enhanced VMXNET, the default number of receive and transmit buffers are 150 and 256,

respectively, with the maximum possible receive buffers being 512. You can alter these settings by

changing the buffer size defaults in the .vmx (configuration) files for the affected virtual machines.


For VMXNET3 and E1000, the default number of receive and transmit buffers are controlled by the guest

driver, with the maximum possible for both being 4096. For Linux, the values for both VMXNET3 and

E1000 can be changed from within the guest by using ethtool. In Windows, the values for E1000 can be

changed in the device properties window.




Reply from Trung:




As I suspected this appears to be a VM setting only in ESX. There does not appear to be a way to set buffers at the host level (i.e. physical NIC) rather than the VMXNET3 or E1000 virtual NICs used by a VM.


Customer is running a BL490c G7 with ESXi 4.1.


Incidentally I have tried to set transmit buffers on a BL460c G7  running Windows 2008 R2 and was not able to go beyond 256.






From Jim:




Yes, number of Ethernet transmit buffers allocated are  64 through 256.


Emulex Drivers for Windows NIC version 4.0.317.0






Hope this helps. Any comments or questions?