Citrix XenServer Slow Network Performance

People new to the virtualization space could get very frustrated when they find out that their Hypervisor of choice preforms much worse than a bare-metal installation. Haven’t the vendors and independent analysis like Project Virtual Reality Check stated that there is no longer any excuses for not running Citrix XenApp on a Hypervisor. The latest numbers shows that the performance are almost the same on XenServer, VMware and Hyper-V.

That being said, to get these high performances requires that you have done your homework and implemented all the Best Practices. Unfortunately there is way to many bugs out there and I’m not even going to start…but I have almost begged Citrix to pay more attention to their own Support Forum in this post.

In this post I’m going to share some important tunings related to poor network performance on Citrix XenServer 5.x family.

Disable Task Offload :

For Windows 2003 VM’s you will need to create a registry key to DisableTaskOffload – REG_DWORD = 1 under HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameter. The easiest way is to create a Group Policy to push this registry key.

Disable CheckSum Offload :

The second fix you should try if you still have poor network performance is to Disable Checksum on the XenServer interfaces, both the Virtual (VIF) and the Physical (PIF). Be aware that you don’t need to restart the XenServer or the VM’s. This script will do this automatically on all you network interfaces in your XenServer Pool.

echo Setting checksum off on VIFs
VIFLIST=`xe vif-list | grep "uuid ( RO) " | awk '{print $5}'`
for VIF in $VIFLIST
do
echo Setting ethtool-tx=off and ethtool-rx=off on $VIF
xe vif-param-set uuid=$VIF other-config:ethtool-tx="off"
xe vif-param-set uuid=$VIF other-config:ethtool-rx="off"
done
echo Setting checksum off on PIFs
PIFLIST=`xe pif-list | grep "uuid ( RO) " | awk '{print $5}'`
for PIF in $PIFLIST
do
echo Setting ethtool-tx=off and ethtool-rx=off on $PIF
xe pif-param-set uuid=$PIF other-config:ethtool-tx="off"
xe pif-param-set uuid=$PIF other-config:ethtool-rx="off"
done

Note :

Please note that this script is provided “as is” and that using this is at your own risk. Please feel free to leave comments below regarding bugs & suggested improvements in future releases.