How far can the fcal cable be and what sort of performace hit do you take on that 3rd loop (since each loop can only consist of 8 shelves)?
As far as performance goes, the three FCAL loops are peers in the system. They are "parallel". Each loop is independently connected into the system via its own FCAL adapter/controller and there is no significant prioritization of requests/responses on any one loop over another.
You figure, the last shelf in the 3rd loop is going to be more than a few meters away from the filer...
Well yes, but distance-from-the-controller is not a significant influencer of device performance on an FCAL loop. This type of fibre channel incorporates some cunning stunts at the MAC layer, borrowed from Token Ring and FDDI, that do an effective job of spreading the available bandwidth betwixt all of the connected players, regardless of their physical position on the loop.
Keith