Switch on San performance

Storage switches have a key role to play in enabling firms to get the most out of their storage area networks. Nick Enticknap...

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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.

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.

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.
This was first published in March 2002



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