I posted this question to et-mgmt-tools after someone asked me about
driver selection in Cobbler.
https://www.redhat.com/archives/et-mgmt-tools/2009-May/msg00037.html
It appears the virtinst library (which is the library underneath Virt
Manager) that we use for Xen installations is not using blktap driver by
default, which is slower for Xen paravirt and may also not handle
unclean shutdowns well (KVM apparently doesn't have this problem).
I wanted to bring this up here first, rather than making a last minute
change to 1.6.5 -- we can possibly change this in a future release
(needs testing) and also for the devel branch.
https://www.redhat.com/archives/et-mgmt-tools/2009-May/msg00037.html
--Michael