I would highly recommend not installing Xenserver or any visualization OS onto an SD card. I tried for several days to get Xenserver stable on the internal SD Card slot on a Poweredge r420 and it would blue screen after 2-3 days. If you want to select the SD card as the boot device, I followed these instructions (you have to change the initrd filename to reflect your version of Xenserver):
If you get this working I would be very happy to know what you did!