What can prevent a successful migration with VMotion?
network cards located in different server slots
a physical CD-ROM that is connected from the virtual machine
different CPU clock speeds
one of the virtual disks that is a mapped SAN LUN
VMware DRS and VMotion: Improve workload balance, prevent problems
Some virtual machines may fail to migrate, whether by automatic VMotion task or if evoked manually. This is generally caused by obsolete virtual machines, CD-ROM binding or other reasons that may not be intuitive