We sold a few systems in the early 2000's with RAID drives. Problem was if one drive failed or had damaged files, the RAID copied the damage to the second drive and you were hosed.
I don't know what RAID # you are using, but we don't recommend this any more.
The RAID backup sw runs in background and causes an unknown load on the system. I'd suspect this first if you are having any anomalies in performance.