HP SAS SFF dual port vs. single port HDD

What is difference between dual and single port HDD? 

-- from HP forum:

If you install the SAS drive in a Proliant it does not matter if you installa a SP or DP drive since only one port will be used by the smart array controller. 

Dual port (DP) drives are intended for redundantly connected configurations like with the MSA60 and 70 and if SAS drives are used in the backend of a storage array like the MSA2000. 

note: Dual Port... "will only support HP-UX and OpenVMS environments and will be available on selected HP Integrity Servers only."

So for win/proliant users the dual port, as of today, provides no benefit.