The multipath driver is installed as part of the Citrix XenServer software.
The following website provides a general overview of multipathing on Citrix XenServer 5.0:
http://support.citrix.com/article/CTX118791
The following website provides the most current information about the IBM configuration file (multipath.conf) for the system:
http://support.lenovo.com/us/en/products/servers/lenovo-storage