VMware: TCP Chimney Offload

What is the recommended TCP Chimney Offload setting for a Windows Server 2008 or 2012 VM running in vSphere 5.1?

Also, is there a special case for SQL server VMs?

Note: Windows Server 2008, this setting is ON by default, while in Windows Server 2012 it is off by default.
Who is Participating?
Andrew Hancock (VMware vExpert / EE MVE^2)Connect With a Mentor VMware and Virtualization ConsultantCommented:

See this VMware Knowledge Base Article for additional verification

VMware KB: Poor network performance on Windows 2008 Server

Hence why it's off now in 2012!
pzozulkaAuthor Commented:
Hmm article doesn't explain why. It's counter-intuitive.

With the advent of 10Gbe NICs, the networking throughput is often limited by the processor speed and its ability to handle high-volume network processing tasks. The CPU is designed primarily for computing and not for I/O, and thus cannot keep up with the data flowing through the network. This causes network flow to be processed ata rate slower than the speed of the network.  THis is where TOE comes in to solve the problem by "offloading" from the CPU.
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
In a virtual environment, the network interfaces are virtual.

Network Driver Interface Specification (NDIS) 5.0 lets TCP take full advantage of intelligence in network adapters by letting the adapter do some of the tasks that the processor normally performs. Offloading these tasks to the network adapter leaves the processor free for tasks that only it can perform.

but if it's not a function of the virtual adaptor.

The OS does not know it's virtualised!
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

All Courses

From novice to tech pro — start learning today.