[fedora-virt] disk perf again

[Tom Horsley <tom horsley att net>]

In my xen virtual machines, I found that switching my disk
image files from file: to tap:aio: made the machines (all
HVMs) run much better with far fewer hangs and glitches.

If I were to try to run with KVM rather than XEN, is there
some equivalent of something like tap:aio that provides
better disk performance, or is the KVM equivalent of file:
the only way to access a disk image in a file?

(I hasten to add I have absolutely no idea what the
heck file: versus tap:aio: means, I just tried it when
I saw it mentioned somewhere and it worked much much
better :-).