Arcserve runs slow

I have ARCserve 6.6 on my Novell 5 box, ARCserve starts at 10:00 pm and finishes at 6:30 am. That’s very slow, any ideas what could cause such a slow backup? I have a Novell 4.11 box with ARCserve 6.6 and it takes only 1.5 hours.