Not sure, You need at least 2 disks for a raid 0 array to operate like it should, after that it shouldn't matter, nor do you have to have an even # of drives. Just remember, the more drives in the array, the higher chance of a failure. western digital says the raptor drives are good for 1.2 million hours, So my 2x raptor array should last about half that or 57 years.
