The value of 'hrStorageIndex' corresponding to the first
associated conceptual row in the 'hrStorageTable' of the
Host Resources MIB (RFC 2790) and an (optional) associated row
in 'xcmHrStorageTable' of the XCMI Ext to Host Resources MIB,
or zero if none.
Usage: A 'chain' of one or more Storage entries in
the Host Resources MIB MAY be associated with a service.