Generally on the back of a recent filer, you'll have
the IOIO port this is an RJ45 connection for serial (RS232) - you should have a short cable to convert it to 9 pin D female
E0M this is an RJ45 connection for management
e0a e0b etc these are normal RJ45 Ethernet ports (1Gb or less)
The wretch/spanner port this is an RJ45 for ACP (management of newer shelves)
SAS ports - rectangular ports for newer shelves
Fibre channel ports for either older shelves or FC hosts.
10GB ports - normally rectangular ports for special short run cables or fibre network connections.
http://support.netapp.com/portal?_nfpb=true&_pageLabel=documentation should have all the info you need.