Para Virtualization or Full Virtualization with Para virt Dirvers??

[Nuwan Alwis]

Hi Guys,
Im involved in virtualization project on RHEL5. According to my knowledge i know that para virt VMs perform better than full virt VMs for sure. I want to know if Full virt VM with Para Virt Drivers installed can perform better or come equal to a Para virt VM.
Note that this is for server consolidation, so please add which type of servers are good to keep as Full Virt and Which is good to keep as para Virt(I dont need OS types, I need eg:Data base servers with external storage is better to keep as Full Virt VMs)

Have a Grate Day Yo...ll..!

[Matti_Kurkela · Accepted solution]

As I understand "full" virtualization and paravirtualization, a system with paravirtualization only in drivers can never quite match a system with complete paravirtualization.

"Full" virtualization = the interface between the VM and the hypervisor is exactly the same as with the real hardware. The operating system of the VM does not neeed to "know" it is a VM.

Paravirtualization = the code "knows" it is running within a VM and is allowed to take certain "shortcuts" as the hypervisor handles the actual hardware.

In other words:
Full virtualization = the operating system of the VM is not at all optimized for working in the virtual environment.

Drivers-only paravirtualization = the drivers are optimized for the virtual environment, but the OS kernel of the VM is not. This has a better performance than full virtualization, but not quite as good as complete paravirtualization.

Complete paravirtualization = the drivers and the OS kernel of the VM are both fully optimized to the virtual environment.

The complete paravirtualization should always have the best performance, but depending on the characteristics of the particular workload, the difference between complete and drivers-only paravirtualization may be insignificant.

For a rule of thumb, remember that the overhead of the virtualization is incurred whenever the application needs to access anything other than CPU or RAM. So an application which is mainly CPU-bound (=number-cruncher) is not going to care much about the virtualization type, but for an I/O-bound application you'll really want as much paravirtualization as you can get.

Of course, there may be other things that limit your choices: if you're moving a legacy system into a virtual environment and are required to limit the changes within the legacy system to absolute minimum, full virtualization is the way to go.

MK