CommScope® Enterprise Data Center Design Guide - Public ...

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Fibre Channel
Fibre Channel (FC) is the primary high-speed network technology for storage networking due to
the protocol’s quality of service, reliable transport (lossless nature) and speed of data transfer.
A fibre channel system can be set up as point-to-point, as an arbitrated loop, or in its most
useful and common configuration, a switched fabric. In a fabric network, the switches manage
the state of the fabric, providing optimized interconnections, and allow multiple pairs of ports
to communicate simultaneously. A high availability (HA) configuration allows for a failure of one
port to be “failed over” to a redundant path, and should not affect operation to the host or
storage devices.
Optical fiber is the typical media utilized for Fibre Channel, although a twisted pair option is
allowed within the standard over shorter distances. FC is commonly available in speeds of 1,
2, 4 and 8 gigabits. Although implementation of 1G speed is trending down, there may be
some need of this lower speed to connect to mainframe storage using 1G ESCON networks.
The industry is moving towards higher data rates now, with 16G speeds in development and
32G speeds on the horizon. Although still in draft form, 16G speeds will likely be capable
with OM3 fiber to distances of 100M, with a potential longer distance option utilizing OM4.
Fibre Channel over Ethernet
Fibre Channel over Ethernet (FCoE) is an attempt to simplify and converge the SAN and LAN
networks at the data link layer. As Ethernet is becoming prevalent in the LAN and even moving
out into the WAN or MAN space, it makes sense to consider a protocol that routes the SAN
over the Ethernet. The FCoE standard was developed by INCITS T11 – The InterNational
Committer for Information Technology Standards and completed in June 2009. FCoE
recognizes that FC will continue to be a dominant storage protocol in the data center, while
also providing for a simplified, consolidated I/O solution.
To implement FCoE, the FC frame has to be encapsulated into an Ethernet frame. Using the
layering models, the top layers of the FC, along with a new mapping layer, are stacked on top
of the Ethernet MAC and physical layers to create the FCoE Frame. To preserve the lossless
nature of FC, the optional PAUSE capability allowed by IEEE 802.3x Ethernet must be used to
allow a busy receive port to send a control frame to the transmit port asking for it to pause
transmission as well. Use of this feature circumvents the traditional Ethernet allowance of
dropped packets. There are other requirements besides the “pause” mechanism required to
make Ethernet lossless. These are part of the Data Center Bridging group of standards under
development in IEEE. Finally the traditional point-to-point addressing of FC is not sufficient, as
Ethernet does not form the same point-to-point connection. A MAC address has to be added as
the first 2 fields of the FCoE frame in order to point to its Ethernet destination. This method of
CEE – Converged Enhanced Ethernet – allows FCoE to exist and its lossless nature
differentiates this from traditional Ethernet.
FCoE is seen as complimentary to the movement towards virtualization. Hypervisors (platform
allowing multiple operating systems to run on a host computer) need to provide guest operating
systems with virtualized storage through a FC network infrastructure. Today it is cumbersome to
move virtual servers to new equipment not just during initial employment, but over the lifetime of
the system for optimization and maintenance purposes. IT managers often use 4, 6 or 8
network adapters in critical applications to cover both Host Bus Adapters (HBA) and Network
Interface Cards (NIC). FCoE enables the consolidation of both SANs and Ethernet traffic onto
a single Converged Network Adapter (CNA), reducing the ever growing number of adapters
required at the server level. FCoE combined with the advent of 10 Gigabit Ethernet (10 GE)
fabrics grants companies the ability to consolidate their I/O, cables and adapters while at the
same time increase the utilization of their servers through virtualization.