Comment # 29 on bug 954452 from Franck Bui

(In reply to Olaf Hering from comment #27)
> libxl supports the domU.cfg files from xend. Their syntax is equal anyway,
> but some aspects of the "old" disk=[] syntax needed an update to handle more
> use cases. In the end this translates to "existing domU.cfg files must be
> supported". This means that even the names of the devices (such as "hda")
> are accepted on the libxl side.
> 
> I'm sure there are domU.cfg files with 'hd?' out there, and TW will simply
> breaks in those VMs. For no good reason.

Currently your the first one reporting a bug for that, and if the name you're
using is considered as a bad practice, then you should rename it instead of
asking for us to support one more hack forever.