Slow Arcserve 4 NT Backups

We have a Compaq Proliant DL380 with a intergrated smart array controller card, and an external DLT 20/40. OS is WIndows NT 4 SP6 and Arcserve 6.5 4 NT (build 620). We are experiencing very slow backups with a throughput rate of about 4 to 7 MB pm.

The jobs backs up the local machine shares & registry and three other NT servers shares & regisrty across the wire, in the same domain. All servers are running at 100Mb on the local switched lan.

Does anyone have any ideas how to increase this. I have searched Compaq, CA & MS, but have only found on document on CA (16005) which we have implemented but with no difference.