An article on Fibre Channel.
-Jay
_________
Fibre Channel Use Accelerates
Al Gillen
December 17, 1997
LAS VEGAS -- Over 5 years ago some of the first pieces of Fibre Channel
technology were put into place through an IBM Corp.-Hewlett-Packard Co.
technology swap. Now, the rest of the world has found a use for that technology.
Today, Fibre Channel is finally poised to replace SCSI technology in at least one
key part of intelligent storage subsystems.
The past several months have seen a steady trickle of Fibre Channel
announcements being made, with a significant splash of products occurring at the
Comdex trade show last month. Yet nearly all of the players in the storage market
are taking an evolutionary approach to replacing SCSI technology with Fibre
Channel in the host-to-subsystem connection, leaving SCSI disks and traditional
RAID controllers within the disk array itself for some time to come. Most industry
observers anticipate a lengthy transitional period between today's pure SCSI
subsystems and the pure Fibre Channel subsystems that may dominate the future.
The attraction of Fibre Channel over SCSI is threefold: It has a significantly smaller
packaging footprint, it is faster, and it can communicate over longer distances.
Fibre Channel Arbitrated Loop (FC-AL) is a serial transmission technology,
requiring only two conductors for a single connection to be established vs. a
68-wire cable required for a "wide" 16- or 32-bit SCSI connection. Current FC-AL
interfaces operate at up to 100 MBps per port, and can be extended physically up
to 10 km, or about 6.2 miles, using fiber optic connections. Ultra SCSI
theoretically supports data transfers of up to 40 MBps over distances of up to 25
meters, or 82 feet. Users can deploy multiple FC-AL ports to increase bandwidth.
FC-AL backers claim sustained data transfer performance in excess of 90 MBps
and transaction rates of at least 25,000 input/outputs per second (IOPS).
Adam Zagorski, product manager with Adaptec Inc. (Irvine, Calif.) says a pure
Fibre Channel system can achieve high efficiency as compared with the theoretical
performance limits. When tested with a Fibre Box FC-AL disk array from Box Hill
Systems Corp. (New York), Adaptec's AHA-F940 PCI-to-Fibre Channel adapter
can sustain up to 97 MBps of data transfer under optimal conditions. Even on more
typical random reads and writes, Zagorski claims that test results of 70 to 80 MBps
is not unusual. "The overhead is very small, so it's very easy to sustain the
bandwidth," he says.
But for now, that level of performance is likely to be the exception rather than the
norm, as the majority of Fibre Channel systems will use a mixed format. Typical of
a hybrid system in the industry is what Digital Equipment Corp. announced earlier
this fall. Digital unveiled its plans for a migration to Fibre Channel technology,
which call for a phased approach to Fibre Channel adoption.
Phase one is shipment of storage subsystems with a factory-configured Fibre
Channel host-to-subsystem link. In effect, the company is replacing the SCSI
connection between host and disk subsystem with a Fibre Channel link, keeping
the other building blocks largely unchanged. The company will phase in a field
grade option during the first half of 1998 for existing units. Full Fibre Channel
systems will follow at a later point.
"For now, we believe we get the best of both worlds by using the Fibre Channel on
the front end and the ultra SCSI on the back end. If all you're going to do is
replace the same architecture and topology today with Fibre Channel disks, there's
not a lot of [benefit]," says Kirby Wadsworth, director of marketing for Digital's
storage business unit. "If you order a new RAID Array from us, you will have
your choice of using the ultra SCSI or the Fibre Channel interconnect," he says.
But, Wadsworth adds, "What's going to happen over time, as the technology
moves and the prices come down, the architectural model will change. We'll be
moving more toward that network array, the storage area network. When you do
that, your entire model changes."
Skip Jones, board director of the Fibre Channel Loop Community (Austin, Texas,
www.fcloop.org) and director of planning and technology for SCSI and FC-AL
adapter and semiconductor technology provider Qlogic Corp. (Costa Mesa, Calif.),
argues that a transitional approach makes sense. "We don't need Fibre in the box --
yet," he says. "Before a year ago, Fibre Channel was only for the most elite,
high-end systems." Even with the broad adoption of Fibre Channel, Jones says it
won't soon grow beyond disk subsystems. "For most peripherals, SCSI will
continue [to dominate]. Most tapes don't need the speed of Fibre Channel. But
inside the loaders, that's a good idea."
In fact, true end-to-end Fibre Channel systems have been a rare commodity until
recently. More than 1 year ago, Box Hill Systems announced its Fibre Box product,
which uses FC-AL disks from Seagate Technology Inc. (Scotts Valley, Calif.) --
the only Fibre Channel disks available until recently -- and a full FC-AL
implementation. The system uses a host bus adapter that connects directly to the
disks without an interim RAID controller. The individual disks use a built-in
intelligence called X/OR RAID, which in effect distributes the RAID parity
processing load to the disks themselves in a distributed architecture. Because the
X/OR RAID capabilities are built into the disks themselves, not a RAID controller
board, other vendors may offer this technology in the future.
But, says Carol Turchin, Box Hill vice president of marketing and strategic
planning, "it's the setup on our X/OR RAID Module which tells the drives what
they should do." She expects other disk vendors to offer this option, but not until
they feel comfortable moving away from the traditional RAID controller engine.
To be certain, the limited availability of end-to-end Fibre Channel disk subsystems
has been caused, in part, by a lack of drives that support the Fibre Channel
interface natively.
That situation has changed. For example, Quantum Corp. (Milpitas, Calif.) has
announced Fibre Channel-ready drives, available first quarter 1998. Other major
drive makers are expected to announce products early next year as well.
It may be several months before these disk drives work their way through to
finished products. When they do arrive, new entries will broaden storage choices,
adding to other products already announced by vendors such as nStore Corp.
(Lake Mary, Fla.) and Data General's Clariion Storage Systems Unit (Westborough,
Mass.).
Comments to Al Gillen, Editor-in-Chief | Last updated December 1997 | Copyright c 1 |
