What is the sripe size on your RAID? If it is really low that could affect performance. Other than that it really sounds like your drives aren't being recognized as connected via ATA133. If it has fallen back to a PIO mode you could expect crappy performance and higher CPU usage. You might try ditching those snazzy round cables for some basic 80 conductors.

-Mike
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EmpMenuX - ext3 filesystem - Empeg iTunes integration