Xserver slowdown

A Xserve (slotloaded) serves AFP and SMB. Only other software is Retrospect server Served volume is 3 striped ATA disks. Backup made via SCSI (ATTO UL3S-66) to an Overland AIT PowerLoader autoloader. After 2-4 days of operation the Xserve slows down and must be rebooted. The kernel process takes up much CPU space. Same results in 10.2.8 and 10.3.1 I get a feeling that it is SCSI related. Anyone else with similar problems?