pass-thru module is the same as running regular internal fabric switch in access gateway mode (Brocade) or NPV mode on Cisco. Basically the module does not have a domain id, never joins the fabric so it reduces complexity of your SAN fabric. If you have regular internal switch that is not running in AG/NPV mode you have a lot more functionality that you may or may not need. The biggest issue that i see with pass-thru modules is that you need to run 1:1 cable connection. So if you have 10 blades in your enclosure, you will need to run 10 cables per pass-thru module down to your SAN director.

and third option is virtual connects, so it's just like regular switch running in AG/NPV, i am sure it's much cheaper than regular fabric switch. The benefit of virtual connect vs regular pass-thru is that you don't need to run 1:1 cables.

http://h18000.www1.hp.com/products/blades/virtualconnect/infrastructure.html

http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00814156/c00814156.pdf

ya , but i recall that this is limited to HP blades

if you can't get virtual connects with your blade server vendor, i would look into getting a regular fabric switch and run it AG/NPV mode.

Hello Dynamox,

if we are going to cascade 2 chassis, 4 switches with MDS director,this require extra licenses ??

not sure what you mean by cascade, license information is documented here

http://www.cisco.com/en/US/products/ps6029/products_data_sheets_list.html