Haven’t you heard about chimney which work as an exhaust in traditional Kitchens and factories?

Now one of the virtual networking features of Hyper-V in Windows Server 2008 R2 is using this word as “VM Chimney” - may be MS wants to emphasize that you got an easy path to flow. Anyway, VM Chimney in Hyper-V allows a VM to offload its network processing load onto the NIC of the host computer. This is something similar to TCP offload scenario, Hyper-V simply extends this functionality into the virtual world. This benefits both CPU and overall network throughput performance, and it is fully supported by Live Migration.

VM Chimney is disabled by default in Windows Server 2008 R2, primarily for compatibility reasons. Vendors like Intel, supports the compatibility for VM Chimney and if you are sure that the hardware you purchased support this – TURN IT ON for a better host system performance and a simultaneous boost to VM network throughput.

Support for Jumbo Frames was first introduced in initial release of Windows Server 2008 to support the hardware and now the same has been extended to support VMs. So, just like improving performance on hardware level, Jumbo Frame capability for VMs now can increase the performance of virtual networking and provides 6 times larger payloads per packet, which improves not only overall throughput but also reduces CPU utilization for large file transfers.