Apple Raid dropping off when doing most data renders

Apple Raid, fully occupied, 3 TB is dropping off when doing renders. Unit is connected via fiber to Mac intel running FCP 7, OS 10.6. Problem has been going on a for a while. Drive will sometimes drop off, when no renders are occurring. Also, drive performance is slower. Although drives are striped all the way accross, front performance meters, do not operate together. Any thoughts as to what is not working?