I noticed the documentation on instances is not entirely correct as it it says:
(KVM) The Instance must not be using local disk storage. (On XenServer and VMware, Instance live migration with local disk is enabled by CloudStack support for XenMotion and vMotion.) Well, I’m using local storage on KVM and I’ve done like 6 live migrations with local storage until now, it worked fine every of those 6 times :) -- Jimmy