if you are Talking Celerra ISCSI (Not Clariion) then you can just configure if you have the license  no extra hardware necessary - it uses the existing Ethernet ports on the blade / data mover  yes you can connect multiple ISCSI clients
Our Celerra is configured as CIFS file server, now we would like to make use of iSCSI with the existing setup.  1) Will there be any impact to the existing setup? 2) What are the harware requirement? 3) Can i connect multiple servers to iSCSI on NAS?    
How to setup iSCSI on celera NAS?