Can anyone explain VPC and VDC for Nexus switches?

The Virtual Device Contexts (VDC) is a new feature introduced in Cisco Nexus 7000 NX-OS, so does it happens to be the first Data Center Switch to provide Virtual Device Contexts (VDC) capabilities. The Virtual Device Contexts (VDC) allows a Cisco Nexus 7000 Series switch to be logically segmented into four different virtual switches (device contexts). The logical separation of single Nexus 7000 into multiple logical devices provides the following benefits:

• Administration and management separation
• Change and failure domain isolation from other VDSs
• Address, VLAN, VRP and vPC isolation.

When the Cisco Nexus 7000 Series switch is first booted, all interfaces of all line cards in the modular switch platform are placed in the default VDC (VDC 1).  Up to four VDCs can be created including the default VDC, but an interface can only belong to one VDC.  Interfaces from different line cards can be placed in different VDCs.  Once an interface is placed into a VDC, the interface can no longer be managed in the default VDC context.

The Cisco Nexus 7000 Series switch shares some components between VDC(s), which include the following:

• A single instance of the kernel which support all of the processes and VDCs.
• Supervisor Modules
• Fabric Modules
• Power Supplies
• Fan trays
• System fan trays
• CMP
• CoPP
• Hardware SPAN resources.
• and VCP

• Nexus vPC is a treamendous cisco feature that introduced with Nexus 2,5 and 7K.

   

  The vPC is actually eleminate the need of STP on the member vPC ports and allow for efficient loadsharing capabilities.

   

  The VSS on the other hand is a feature introduced with Cisco 6500 catalyst, its basically combines the Backblane throughput of the two syatems which allows for high forwarding rate between ports, it also simplifies the managment by making two physical switch operate as one logical Switch.

   

  Both are amazing features, however, the vPC is a special from my point of view, I wasnt thinking one day Cisco is going to replace/disable STP with such feature , be noted that vPC uses duplicate frame detection to prevent loops and STP would still be running on the background incase of a failure of any of the vPC links, but the idea is a mazing.

   

  Below is an excellent comparison and a link to a good discussion about vPC, you will find in this link also a file contains comparison between both vPC and VSS:

   I hope this help