What io scheduler to use inside guest VM?

[Piavlo <piavka@cs.bgu.ac.il>]

 Hi,

I use LVM volumes as guest VM disk.
I'm wondering if setting setting the io scheduler inside linux gest has
any effect (with virtio disk  driver and with emulated scsi or ide driver)
And if it has affect what's better choice ? My thoughts is that if
changing the  scheduler inside guest has affect - then it's probably
best to use noop scheduler inside the guest
and let the hypervisor linux decide according to it's scheduler.
So what I don't understand is if there are two levels of io scheduling ,
one inside the guest (the redundant one and setting it to noop will
minimize it's affect) and other inside the hypervisor linux?(or just one
level in the hypervisor)
Probably with virtio driver tthere is no io scheduling inside the guest,
but is it so with emulated drivers too?
And also is there any difference in io scheduling if I use image file
instead of LVM?

Thanks a lot
 Alex