Eu seguiria esta configuração: debaan.blogspot.fr/2014/10/xenserver -boot-from-iscsi.html
também de acordo com este post:
UPDATE: XenServer boot from iSCSI (at least with iBFT) is just plain awful. Don't bother. Multipath does not work. Too many hacks to try to get things to work. It is not supported, anyway, and it will probably break every time you do an upgrade. Plus, the NICs that you use for iSCSI boot will be unusable for any other purpose. This is aspect of XenServer is very immature and not robust.