Running XENU on vnodes.

Hi.

I created and partitioned a vnode device and installed NetBSD to it.
It runs as a XENU host:
disk = [ 'file:/vserv/netbsd/nbsd1,xbd0a,w' ]
My question is how (if) running of XEN in a vnode device affects
system's speed. I'd like to use such setups in production enviroment
running mail server and sql server on XENU hosts inside vnd devices.
Would there be any particual perfomance loss if I chose to run my XEN
'guests' on vnd devices instead of a separate HD partition?

Cheers,
Marcin.