Monday, September 26, 2011

VMware ESXi 4.1 Optimizations for Cisco UC on UCS

In my previous post I discussed the importance of installing the latest version of VMware Tools on UC virtual servers in a Cisco UC on UCS deployment. A second and equally important VMware 'tweak' is disabling Large Receive Offload (LRO) on VMware ESXi hosts.

VMware Knowledge Base Article 1027511 addresses some Linux TCP/IP stacks perform poorly when handling LRO-generated packets. This results in poor TCP performance.

    Cisco UCS Servers at VMworld
  1. Log into the ESXi host or its vCenter with vSphere Client.
  2. Select the host > Configuration > Software:Advanced Settings.
  3. Select Net and scroll down slightly more than half way.
  4. Set the following parameters from 1 to 0:
    1. Net.VmxnetSwLROSL
    2. Net.Vmxnet3SwLRO
    3. Net.Vmxnet3HwLRO
    4. Net.Vmxnet2SwLRO
    5. Net.Vmxnet2HwLRO
  5. Reboot the ESXi host to activate these changes.

Your guest VMs should now have normal TCP networking performance.

References:
http://docwiki.cisco.com/wiki/Disable_LRO
VMware Knowledge Base - KB Article 1027511
Cisco UC on UCS - Don't Forget VMware Tools

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