From the documentation:

"In addition to supporting Generation 2 modules, the Cisco MDS 9500 Series Switches and the Cisco MDS 9222i Switch support another set of modules called Generation 3 modules. Similar to Generation 2, each Generation 3 module can have one or more ports in port groups that share common resources such as bandwidth and buffer credits.

Generation 3 Fibre Channel modules are supported on the Cisco MDS 9506 and 9509 switches with Supervisor-2 modules, and on the MDS 9513 Director with Fabric 2 modules. The MDS 9222i switch supports the 4/44-port Host-Optimized Fibre Channel Switching module. MDS NX-OS Release 4.1(1) is required to support the Generation 3 modules."

http://cisco.biz/en/US/docs/switches/datacenter/mds9000/sw/4_1/configuration/guides/fm_4_1/gen2.html#wp1700496

The 8GB modules are Generation 3 modules.

Brian