Having 8 active paths would be overkill. Vplex uses the Adaptive PP policy which assigns IOs based on an algorithm taking into account path load and logical device priority. During a path failure PP marks the failed path for testing so it is no longer sending IO down it. it also prioritises the testing of the remaining  paths to avoid common shared path failures.  The quicker these paths can be tested the quicker IO's can be sent down them.  If there are more than the recommended paths (say 8 paths) then the application may experience time-out issues while waiting for the PP to complete its testing and algorithm calculations.  [URL]  checkout this link - page 23 (Proactive path testing on failures)
The VPLEX best practices recommend a maximum of 4 active paths to a back-end LUN:  VPLEX recommends a maximum of 4 active paths per director to a given LUN (Optimal). This is considered optimal because each director will load balance across the four active paths to the storage volume.    Is there a more detailed reasoning behind this recommendation? What happens if for example there are 8 active paths to a LUN? What would the downside be?
back-end maximum active paths