Slow backup performance of ArcserveIT

I have problem about low backup performance of arcserveIT6.6 in netware 5.1.I have checked from novell web side and recommend to set some parameter but after set it also poor performance.PLease see h/w and s/w profile below.
Hardware profile:
Backup server:Compaq proliant 370
Tape:HP DLT 35/70
Remote backup server:Compaq proliant 530
Software profile:
ArcserveIT 6.6 with service pack (build 111.239 01/10/00)
Currently backup performance:
Remote backup :432 KB/S
Local backup : about 1.4 MB/S
Have any idea from you to increase performace?
Thanks,