XenServer supports 3 different types of storage repositories (SR)
1) File based vhd, which is a local ext3 or remote NFS filesystems, which supports thin provisioning for vhd
2) Block device-based vhd format (SAN based on FC, iSCSI, SAS) , which has no support for thin provisioning of the virtual disk but supports thin provisioning for snapshots
3) LUN based raw format - a full LUN is mapped as virtual disk image (VDI) so to is only applicable if the storage array HW supports that functionality