If my EVA does an implicit lun transition, the esx servers themselves would not detect a path failure, correct? As this is the backend controller changing ownership the esx hosts still send IO to the same path – so no path failure right?
As the implicit transition happens, is there any issue sending IO to either controller?

Scenario. lun is owned by sp0 and most IO is coming through sp1 (and has been for a while). However, some IO is coming through sp0 also. EVA initiates an implicit transition from sp0 to sp1. during which time IO still comes in to both sp’s for that lun….what will happen?

However, for Frank’s point, assuming you have presented the same LUNs to each server, my script should assign the same path to every server the same way, so that the managing controller issue should be moot. If all the hosts are accessing LUN 5 via path 5 (which goes to controller 2) then the EVA should switch the managing controller for that LUN to #2.

Although an EVA is listed as an Active\Active Storage Array, Eva’s assigns a managing controller to a virtual disk (LUN). When an I/O is send to the second, non-owning controller, the I/O is send by this controller to the owning controller. Communications between controllers are really fast, but it’s still an unnecessary extra command.
In command view eva, on the present tab you can see which controller is the managing controller. Configure the preferred paths aligned with the managing controller.