Comment # 8 on bug 954452 from Olaf Hering

The strings for a given block device are "free strings", that means a given
block driver is free to pick any name. It just happend that IDE used to pick
hd, SCSI picked "sd" and so on. In the early days the PV drivers used to claim
the well known names and their major:minors to make it easier to install and
run existing distros.

Today the names can be still passed into the guest. For some reason I picked
"hd" instead of "xvd" for my PV guests. So that part might be fixeable by
adjusting both the domU.cfg and also the used devicenames within the VM. In the
end I would call this a regression. "hd" per se has no relationship to IDE
hardware anymore, as explained above. Please restore "hd" support, I'm sure
such names are in use.

Not sure why the HVM guest fails. Here the "hd" in domU.cfg has additional
meaning, it tells qemu to create an emulated IDE controller which is later
driven by the SATA drivers. Have to see how to debug this.