The HBA has 4 ports, a- d but only 2 ASICs (Application Specific Integrated Circuits).
One of the ASICs controls ports a & b, and the other controls ports c & d.
In your case, this makes the ASIC a single point of failure.
You should use either ports a & c or ports b & d.
That way, even if one of the ASICs should fail, you will still have connectivity to the disk shelf.