Fibre Channel, CEE, and FCoE –
25
what they’re really all about
TECHNOL
As with all new technologies, first comes the hype, and then reality (and
complexity) kick in, as Leo Kappeler, SE Director EMEA at Brocade, explains.
OGY
F
Over the last ten years, Fibre for the server can be fatal: wants to send packets, the IBRE CHANNEL
Channel has become the usually a server failure or at network node waits for a short,
standard technology worldwide least the failure of important specified amount of time during
for Storage Area Networks applications. On the operating which no data can be sent on
(SANs) and external storage system side, there are also no the cable (“Carrier Sense [CS]”)
systems in the mid- and high- mechanisms for catching such before sending the data
end ranges. Especially in terms fatal errors. The cable packets. If two or more network
of external storage systems, connections that Fibre Channel nodes attempt to send data
Fibre Channel has slowly but replaces can thus be over the cable simultaneously
surely replaced parallel SCSI as considered extremely critical. (“Multiple Access [MA]”), both
the standard interface. are corrupted, i.e. a “collision”
Ethernet and its occurs. All network nodes are
Today, Fibre Channel is, and will protocols equipped with “Collision
remain, the de facto standard Ethernet was developed about Detection (CD)”, so that they
on the data storage market for 30 years ago out of a need for know which data blocks were
many years. different computers to not transferred. There is no
exchange data directly and use form of acknowledgement.
To describe Fibre Channel as common resources (e.g.
merely “another network printers). In other words, to It is obvious that this
protocol” would not do justice connect autonomous computer rudimentary CSMA/CD protocol
to the actual demands of the systems. will quickly outgrow its
data storage market. In usefulness. However, Ethernet
comparison to the classic and Although it is inconvenient was already very widely
most successful network when this connection fails, the distributed, relatively
technology, the Ethernet, there networked computers do not affordable, and simple to use.
are several concrete also fail as a result. For this The solution for more complex
differences. reason, and also to keep the demands and high scalability
infrastructure cheap and was provided by “Top Level”
Let’s start with the fundamental simple, a “Collision Domain” protocols. TCP and IP (TCP/IP)
development requirements: was created for use with are the two most commonly
In essence, Fibre Channel must Ethernet, i.e. an environment of used today. Unfortunately, this
replace the cable between network nodes with a clear has caused a dramatic rise in
server and storage, supplying addresses (MAC addresses) both the protocol overhead and
in effect a very fast and reliable that are linked together in a latency times. While modern
connection between these chain (Daisy Chain) connected Ethernet-based LANs really
system components. If this to the same medium (cable). All don’t have much in common
connection fails, even for just nodes receive all data packets with the initial Ethernet
an extremely short time, or if and use the MAC address in the configurations, Ethernet is still
individual data blocks are lost, block header to verify that the based on the same protocol
changed, or transferred in the packet was sent to nodes on standard, with the same
wrong order, the consequences the same network. If one node disadvantages.
WWW.SNS-UK.CO.UK JUNE 09
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