SAS-Lanes and SAS-Expander quesitons - eviltoast

Hey guys!

I own a HP Server with a p408i-a. I have connected it to a SAS expander.

8 Slots of the SAS Expander are filled with the front disks in the server. 2 Slots are connected to the RAID-Controller. So far so good, everyhing is working. I want to connect another SAS-Device to my expander - will it work?

The p408i-a has 8 SAS lanes. Do I need 1 lane per available/used slot on the expander? Or is it just total bandwidth? Somehow I couldn’t find any information about that online. Any help? :)