I will bring up a point for the original poster- more than likely having more than 1 array will lower performance, this may depend on the raid card, but I have tested a few in this exact scenario, and they have all lowered their speed when adding a 2nd array, or even just adding a stand alone drive as a JBOD will bring down your main array speed. This is because the card is forced to share its cache, with reduced cache available to the array, less data is allowed in the cache for any single array, so you loose the performance of that high speed buffer.
I tested this running dd of large files to/from separate disks/arrays.
I tested this running dd of large files to/from separate disks/arrays.