1. identify your Tape connected to your FAS via FC with "sysconfig -t" on the console. Than in Arcserve, Device Configuration choose "NAS Server" and next. Click "add" "NAS Server" and type in the IP of your FAS. Compete it by filling in user name & password. After that click "add" "Tape / Changer device.
Here you have write in the name of your tape you've found at the console (for example nrst0a). That's it.