Openstack Compute node performance

[sandeepkumar]

Hi all, 

Am starting to learn openstack. As per my understanding (after reading all the docs) is that the compute nodes run a host OS (ubuntu or other linux) and on top of that you have your hypervisor (like KVM) and then the VMs run on top of it i.e HW -> OS -> Hypervisor -> VMs . This is similar to having a VM running on Virtualbox which runs on a host operating system i.e HW-> Host OS ->VBox -> VMs.Please correct me if my understanding is incorrect.

Assuming my first understanding is correct, How will the performance of the VMs on the this architecture be compared to running the VMs directly on hypervisor i.e HW-> Hypervisor (KVM)->VMs ?

Comparing this with VMWare openstack architecture where Nova speaking to VMWare vCenter and then vCenter manages the ESXi nodes (vCenter and ESXi are on different nodes). This way my VMs are directly running on top of hypervisor connected to HW (HW->ESXi->VMs).And all the overlay networking is handled by NSX. This looks much more performant compared to the other architecture. Am i missing something here ?

Thanks in advance.