As discussed in previous 2 posts, traditional Data Centers typically have multiple networks to handle various types of network traffic for example, an Ethernet LAN for TCP/IP communication and an FC SAN for FC communication. 
 
TCP/IP is typically used for server-to-server communication, data backup, infrastructure management communication, and so on. FC is typically used for moving block-level data between storage systems and compute systems. 

To support multiple networks, servers or hosts in a data center are equipped with multiple redundant physical network interfaces for example, multiple Ethernet and FC network adapters. In addition, to enable the communication, different types of networking switches and physical cabling infrastructure are implemented in data centers. The need for two different kinds of physical network infrastructure to deploy the traditional FC SAN & LAN networks increases the overall cost and complexity of data center operation.

To address the above drawbacks, we have a new type of SAN geerally known as Fibre Channel over Ethernet (FCoE) SAN. This new type of SAN uses the Converged Enhanced Ethernet (CEE) functionalities to send the FC traffic over the enhanced ethernet infrastrucuture.

Fibre Channel over Ethernet (FCoE) SAN Overview

FCoE SAN is a Converged Enhanced Ethernet (CEE) network that is capable of transporting FC data along with regular Ethernet traffic over high speed (such as 10 Gbps or higher) Ethernet links. 
FCoE

It uses FCoE protocol that encapsulates FC frames into Ethernet frames. FCoE protocol is defined by the T11 standards committee. FCoE is based on an enhanced Ethernet standard that supports Data Center Bridging (DCB) functionalities (also called CEE functionalities). DCB ensures lossless transmission of FC traffic over Ethernet. 

FCoE SAN provides the flexibility to deploy the same network components for transferring both server-to-server traffic and FC storage traffic. This helps to mitigate the complexity of managing multiple discrete network infrastructures. FCoE SAN uses multi-functional network adapters and switches. Therefore, FCoE reduces the number of network adapters, cables, and switches, along with power and space consumption required in a data center.

FCoE SAN Components

The key FCoE SAN components are:
  • Network adapters such as Converged Network Adapter (CNA) and software FCoE adapter
  • Cables such as copper cables and fiber optical cables
  • FCoE switch
Converged Network Adapter (CNA)
The CNA is a physical adapter that provides the functionality of both a standard NIC and an FC HBA in a single device. It consolidates both FC traffic and regular Ethernet traffic on a common Ethernet infrastructure. CNAs connect hosts to the FCoE switches. They are responsible for encapsulating FC traffic onto Ethernet frames and forwarding them to FCoE switches over CEE links. 
 
They eliminate the need to deploy separate adapters and cables for FC and Ethernet communications, thereby reducing the required number of network adapters and switch ports. 
 
A CNA offloads the FCoE protocol processing task from the compute system, thereby freeing the CPU resources of the compute system for application processing. It contains separate modules for 10 Gigabit Ethernet (GE), FC, and FCoE Application Specific Integrated Circuits (ASICs). 

Software FCoE Adapter

Instead of a CNA, a software FCoE adapter may also be used. A software FCoE adapter is OS or hypervisor kernel-resident software that performs FCoE processing. The FCoE processing consumes hosts CPU cycles. With software FCoE adapters, the OS or hypervisor implements FC protocol in software that handles SCSI to FC processing. The software FCoE adapter performs FC to Ethernet encapsulation. Both FCoE traffic (Ethernet traffic that carries FC data) and regular Ethernet traffic are transferred through supported NICs on the hosts.

 
FCOE Switch
 
An FCoE switch has both Ethernet switch and FC switch functionalities. It has a Fibre Channel Forwarder (FCF), an Ethernet Bridge, and a set of ports that can be used for FC and Ethernet connectivity. FCF handles FCoE login requests, applies zoning, and provides the fabric services typically associated with an FC switch. It also encapsulates the FC frames received from the FC port into the Ethernet frames and decapsulates the Ethernet frames received from the Ethernet Bridge to the FC frames.
 
Upon receiving the incoming Ethernet traffic, the FCoE switch inspects the Ethertype  of the incoming frames and uses that to determine their destination. If the Ethertype of the frame is FCoE, the switch recognizes that the frame contains an FC payload and then forwards it to the FCF. From there, the FC frame is extracted from the Ethernet frame and transmitted to the FC SAN over the FC ports. If the Ethertype is not FCoE, the switch handles the traffic as usual Ethernet traffic and forwards it over the Ethernet ports.


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