After configuring UCS Service profile, installing VMWare ESXi and configuring Nexus 1000v, i found VMWare vmnics were showing 20 gbps per nic. It was little confusing for me as each UCS Server port from blade to Fabric Interconnect should show 10 gbps. I started exploring it and found an interesting design of Cisco UCS VIC Cards 1340/1380 or UCS Port expander.
As you can see there is hardware port channel between the virtual nics, and the outward ports connected to the IO modules.
As you can see it depends upon different type of connectivity between VIC cards and IO Modules, if you are connecting VIC 1340 without port expander then hardware port-channel see only two 10 gig interfaces connected to it and it presents 20 gig connections to each server Ethernet link, vmnic on ESXi in our case. And if a port expander is connected then the hardware port-channel sees four 10 gig interfaces connected to it so it represents as 40 gig connection for each Ethernet link down the Server. This bandwidth is provided only when UCS IO Modules of 2208xp are installed, if the IO Module 2104 is installed then the bandwidth will be reduced by half, as only four 10 gig connections are provided from 2104 IO module to each blade Server.