Storage switches have a key role to play in enabling firms to get
the most out of their storage area networks. Nick Enticknap looks
at the latest developments
Storage area networking is still in its infancy, but it is evolving
fast. Users are now concentrating less on the basic viability of
Sans and on setting them up, and more what they allow you to do. As
Robin Pilcher, European marketing director at storage networking
specialist CNT, says, "The question now is not do I need a San? It
is what can I do with it next?"
Helping this process is progress in the storage switch arena, which
is rapidly becoming big business. IDC estimates the value of the
storage switch market will exceed $1bn (£700m) in 2003.
The major development last year was the arrival of the FC-SW-2
standard, which was ratified by the American National Standards
Institute (Ansi) in June. This has removed one of the major areas
where standards were lacking - switch interoperability.
The problem dates back to the arrival of the Fibre Channel Fabric
Protocol in 1999. This was a major advance on the Fibre Channel
Arbitrated Loop (FC-AL) protocol which preceded it. It is a
connectionless, frame-based protocol (as opposed to the
connection-oriented, circuit-based FC-AL).
Peter Coleman, director of network supplier Gadzoox , explains, "It
defines up to 16 million addresses; defines name servers, security
servers and management services; and also defines a routing
protocol specifying how information is transported across the
fabric."
Just two years later, the FC-AL standard has become legacy, and the
Fabric protocol (as it is usually known) is implemented by
virtually all San products sold today.
But the routing protocol quoted by Coleman has proven to be a major
weakness of the Fabric protocol. It was intended to ensure switch
interoperability, but this did not happen.
The standard in question was known as FC-SW. The definition was
inadequate and, as a result, every supplier enhanced the standard
in its own proprietary way. This meant switches from one supplier
could not interoperate with switches from any other supplier. So
users were locked in.
The switch suppliers soon realised that their best interests were
served by encouraging interoperability between each others'
products. Five major companies - Ancor (now QLogic), Brocade,
Gadzoox, McData and Vixel - formed a consortium to develop a
standard. They based this standard, which is now known as FC-SW-2,
on the routing protocol used by the market leader, Brocade, called
Fabric Shortest Path First (FSPF).
The consortium's draft FC-SW-2 standard was ready by the end of
2000, and was submitted to Ansi's T11 committee, which is
responsible for all Fibre Channel standards, for
ratification.
Ansi completed its work in June last year. In the meantime, all the
switch products introduced in 2001 featured compatibility with the
draft standard, so the switch suppliers were ready when Ansi's work
was done, and only had to implement the minor changes which
resulted from Ansi's vetting process.
Switch interoperability benefits users in two ways. It makes it
easier to merge or interlink two Sans that have been built using
switches from different suppliers. And it gives users the choice of
changing switch suppliers when upgrading or enhancing a San.
But FC-SW-2 does more than merely ensure all the switch suppliers
route traffic around the network in the same way. It also
incorporates functionality not present in the original
standard.
Most importantly, it increases the self-configuration capability,
and so makes switches easier to install. They are also easier to
manage, because there is greater exchange of zoning capability
information (zoning is the name given to the technique used to
allocate different parts of storage devices to different
servers).
Another major development during 2001 was the arrival of a 2Gbit
switching standard, which doubled the speed at which traffic
travels around a San.
As yet, it has had little impact on installed Sans, because to take
full advantage of it you need every component of the San to be
compliant - the servers and the storage devices as well as the
switches. Host bus adaptors, which provide this capability for
servers and storage devices, have been available for many months,
but relatively few suppliers offer them as an option.
So 2Gbit switching is currently mainly used in the heart or core of
the network, where the higher speed is of greatest value. Paul
Talbut, chairman of Fibre Channel Industry Association (FCIA)
Europe, explains, "Its main use is in the backbone and inter-switch
links, to provide high-speed backbones between switches."
This is similar to the situation with Gigabit Ethernet. Here too
the higher-speed devices are first being used at the heart of
Ethernet Lans, with slower speed transmissions at the edges.
An important feature of the 2Gbit standard is that it is
backwards-compatible with the 1Gbit standard.
All the major switch suppliers except McData have now announced
2Gbit-enabled switches (and McData is promising one for the first
quarter of this year).
Gadzoox was the first, with the Slingshot 4218, launched in April
2001. This represents a move up for the company into the
departmental sector of the market; previously it concentrated on
the low-end workgroup sector with its Capellix products, which
remain in the catalogue.
Slingshot offers 18 ports in a box one rack unit (1.75 inches)
high, priced at less than $1,000 (£700) per port. This illustrates
how the switch interoperability provided by FC-SW-2 is stimulating
competition: prices for 1Gbit switches were typically between
$1,500 and $2,000 per port.
Vixel announced its 9000 Series in May. The products offer full
duplex speeds of 400mbps at each port. There are currently
eight-port and 16-port versions, and also high-availability
models.
Brocade announced its 2Gbit switch, the 3800, in October. Like its
competitors, it conforms to the FC-SW-2 standard, but also
incorporates many other new features. It supports 16 ports, and has
redundant power supplies and cooling facilities. Pricing is set at
about 15% above that of the company's successful 1Gbit products, at
$1,700 to $1,800 per port.
Last year also saw the industry start to concentrate on IP-based
storage area networking for the first time. There are two main
drivers here. At the low end, the requirement to install a special
network just for storage is expensive and time-consuming, while the
performance benefits offered by Fibre Channel compared with
Ethernet are not so important.
For larger companies, a major defect of Fibre Channel is that the
geographical size of the network is limited to about 100km. For
some purposes, such as remote back-up and mirroring, this is a
constraint. Many users have Sans in different locations and want to
be able to link them. IP is the obvious choice, as this allows
connections to be made via the Internet. Most Lans also employ IP
protocols.
This has led to the development of methods for using IP-based
transmissions to connect one Fibre Channel-based network with
another. The Internet Engineering Task Force is working on three
different
IP-based standards - FCIP, IFCP and iSCSI. This seems too many, and
it is likely that in the long term some will not survive. However,
the jury is still out on which one will prevail, as none of the
standards has been fully ratified yet.
At the moment, you need a special-purpose device at the edge of
your network to provide the necessary conversions out of and back
into Fibre Channel, such as the range of routers and directors
offered by CNT. This company announced its first Ultranet Storage
Director as far back as 1997, for transmitting mainframe-based data
over wide area networks. It has since become one of the first
companies to offer products for Fibre Channel over IP, launching
its Ultranet Storage Router products in early 2001.
CNT's product range provides for conversion between Fibre Channel,
SCSI and Escon, and also caters for transmission over ATM, T3/E3
and FDDI networks.
It seems likely that eventually storage switches will take on
responsibility for Fibre Channel to IP conversion. Certainly
Brocade thinks so. It announced a multiprotocol switch, the 12000,
in April last year. This will support both iSCSI and FCIP when the
standards are ready. Further ahead, it will also allow Infiniband
to Fibre Channel bridging. It comes with 64 or 128 ports.
Paul Trowbridge, Brocade's European marketing director, says,
"People are interested in iSCSI and Fibre Channel over IP. They are
technologies which are going to extend the reach of Fibre Channel
Sans."
For the future, progress is likely to focus on improving management
capabilities, especially through the FC-GS2 and FC-GS3 standards
(GS stands for general services).
"They are standards that will increase features." says Talbut.
"Improving the degree of security in the San; authentification
services; the ability to distribute encryption keys across the San;
access control services and lock services - increased zoning
capability."
Around the middle of this year we can expect a 10Gbit switching
standard. Sensibly, there is a merger at the physical level here
with Ethernet, so the actual plugs and sockets will be identical.
The differences between Ethernet and Fibre Channel will then be
confined to the logical, protocol, layers.
But switch products incorporating the new standard are unlikely to
become available before 2003.
Hubs and switches
Three types of component are used in
storage networks to link storage devices to servers:
Hubs
Hubs were the original storage network connectivity devices, and
date back to 1996, when the FC-AL (Fibre Channel-Arbitrated Loop)
standard was still dominant. They are little more than
concentrators, with virtually no intelligence.
Switches
Switches started to replace hubs in 1998. They can support
concurrent conversations between multiple servers and storage
devices, so permit a lot more flexibility. The major switch
suppliers are Brocade, Gadzoox, McData, QLogic and Vixel.
Switches can be core switches - basically devices that are
connected to other switches - or edge switches, which are mainly
connected to servers and storage devices. There is no technical
distinction between them. Edge switches tend to be smaller, with
eight or 16 ports, whereas core switches extend to 32 ports.
Directors
Core switches are sometimes known as
directors. They typically have more high-availability features than
edge switches, as well as being larger, supporting up to 128 or
even 256 ports. There are two major suppliers in this market,
Inrange and McData. There is no precise technical distinction
between a switch and a director.
Connecting fibre channel SAPS to IP networks
"Customers
are looking to the next step in San technology - creating an
enterprise San that spans the globe. That is why IP is important",
says Paul Talbut, chairman of the Fibre Channel Industry
Association Europe. There is an emerging range of standards which
allow users to connect Fibre Channel Sans to existing Lans,
intranets and wide area networks (including the Internet). Known as
FCIP, IFCP and iSCSI, all three are being developed by the Internet
Engineering Task Force.
FCIP With FCIP (Fibre Channel over
IP), the Fibre Channel frame is encapsulated within IP for
transmission over the Internet or other IP network. At the other
end, you simply remove the packaging to have Fibre Channel data
again.
IFCP IFCP (Internet Fibre Channel Protocol)
translates the Fibre Channel packet directly to IP format. So you
do not need a Fibre Channel device or San at the other end of the
IP link, but you do need another IFCP conversion device.
ISCI
iSCSI is SCSI over IP. It removes the need for
Fibre Channel altogether. It allows Sans to be constructed using
any TCP/IP network, opening up the potential for low-cost,
low-performance Sans. iSCSI can also be used in the same way as
FCIP and IFCP to link Fibre Channel Sans over long distances.