Multipathing is the technique of creating more than one physical path between the server and its storage devices. It results in better fault tolerance and performance enhancement. Oracle VM supports multipath I/O out of the box. Oracle VM Servers are installed with multipathing enabled because it is a requirement for SAN disks to be discovered by Oracle VM Manager.
Any system disks (disks that contain / or /boot) are blacklisted by Oracle VM Manager and are not available for use in an Oracle VM environment.
Multipath configuration information is stored in
/etc/multipath.conf on each Oracle VM Server and
contains specific settings for Oracle VM along with an
extensive set of configuration details for commonly used SAN
hardware. In most cases the user should not need to modify this
file and is advised not to. Examining the contents of the file may
be useful to better understand how it works in Oracle VM and
what may need to be configured if your SAN is not using
multipathing and your LUNs are not appearing.
More detail on how multipathing is configured is covered in Enabling Multipath I/O Support in the Oracle VM Administrator's Guide.