Fibre
Channel For Sans Book
Introduction
Fibre Channel technology is
over a decade old. How successful has it been?
Here is an illustration. The
first edition of this book included a section
called “The Unification of LAN
and Channel technologies,” which
described how Fibre Channel
would be part of a trend towards convergence
between LANs and channels. LANs
(Local Area Networks) are used for
computer-to-computer
communications, and channels are high-efficiency,
high-performance links between
computers and their long-term storage
devices (disk and tape drives),
and other I/O devices.
Since then, the prediction has
come true, in three quite different ways.
• Most important has been the
introduction and widespread use of the term
“Storage Area Network,” or SAN,
describing a network which is highly
optimized for transporting
traffic between servers and storage devices.
• At the physical layer, the
LAN and Fibre Channel technologies have
become nearly identical —
Gigabit Ethernet and Fibre Channel share common
signaling and data encoding
mechanisms, and the future 10 Gb/s
Ethernet and Fibre Channel are
expected to share nearly the same data rate.
• The management methods for
Fibre Channel SANs have steadily
approached the traditional
methods used for LAN management, although
the current level of management
effort required for Fibre Channel SANs is
still higher than for LANs.
Interestingly, however,
although the LAN and SAN types of computer
data communications have
converged at a technology level, they have so far
stayed quite different in how
they are used and how they are managed. That
is, systems are usually built
with the SAN storage traffic separated on separate
networks from the LAN traffic,
so that the management, topologies, and
provisioning of each network
can be optimized for the types of traffic traversing
them.
The trends that originally
motivated the creation of Fibre Channel have
continued or accelerated. The
speed of processors, the capacities of memory,
disks, and tapes, and the use
of switched communications networks have all
been doubling every 18 to 24
months, and the doubling period has in many
cases even been steadily
shortening slightly. However, the rate of I/O
improvement has been much
slower, so that devices are even more I/O limited.
The continuing observation is
that computers usually appear nearly
instantaneous, except when
doing I/O (e.g., downloading web pages), or
managing stored data (e.g.,
backing up file systems).
Fibre Channel, and Storage Area
Networks, are focused at (a) optimizing
the movement of data between
server and storage systems, and (b) managing
the data and the access to the
data, so that communications are optimized as
