Is Fibre Channel losing SAN dominance?
- By Brian Robinson
- Dec 05, 1999
If you follow the conventional wisdom as you prepare to build your agency's new storage-area network (SAN), then Fibre Channel will be the technology you use to connect servers, network equipment and storage devices. But is Fibre Channel your only option? What about SCSI or Ethernet links - two proven and affordable alternatives?
Although many issues about Fibre Channel need to be resolved, such as product availability and interoperability, the consensus remains that it is the best candidate for providing SAN connectivity. "Fibre Channel is to SANs what Ethernet is to [local-area networks]," said Rick Luttrall, senior manager for storage marketing at Dell Computer Corp. "It's a key enabler."
Technically speaking, SCSI or Gigabit Ethernet could make a play in SANs, said Roger Cox, chief analyst for server and RAID storage for Dataquest, "but it's not likely." Dataquest projects that the Fibre Channel infrastructure market, largely a result of the demand for SANs, will grow from $478 million this year to about $3.4 billion in 2003.
The idea behind setting up a dedicated network for storage - the SAN - is to offload storage traffic from the enterprise's general-purpose data network. To perform this role, the SAN must meet several requirements:
* It must share storage devices among systems, and it has to be able to scale well as the number of storage devices increases.
* The SAN must be able to shift large blocks of data at high speeds.
* And it must ensure fast data access and backup while maintaining data integrity.
SCSI falls short in several areas:
* It is designed for point-to-point connections between the computer and storage device, and can support multiple host-to-device connections only with difficulty.
* It also can stretch no farther than 25 meters between devices, limiting storage to a limited area close to a host server.
* Its typical data throughput of 40 megabytes/sec is no match for the transfer speeds needed by current multimedia and database applications.
Gigabit Ethernet's nominal data rate does match the current 100 megabytes/sec of Fibre Channel, but Ethernet typically suffers at least a 10 percent overhead load, something that can increase depending on how many devices are on the network.
Also, Ethernet is designed to carry small packets of data across an IP network using a "best effort" scheme, to be collected and combined at the target address. Apart from the need to handle much larger blocks of data, backup memory processes on a SAN require guarantees that can't be met by the best effort method.
Fibre Channel, on the other hand, provides high data rates via fiber-optic links of up to 10 kilometers, supports up to 127 devices on a single Fibre Channel loop and, by using a credit-based system, can guarantee transfers of large blocks of data. Fibre Channel also can handle simultaneous transmission of different protocols, such as IP and SCSI.
However, that doesn't mean Fibre Channel will be used for every connection in a SAN. There is a huge legacy base of SCSI devices that has to be brought into the mix.
"The answer is to move to Fibre Channel and provide adapters out front in order to link to SCSI peripherals," said Aloke Guha, vice president and chief architect at Storage Technology Inc. "We have installed some 250 SANs worldwide, and all have gone this route."
The Education Department is not using SANs, said Jeffrey Conklin, director of systems engineering, but plans to do so in its next round of mass storage deployment due next year. It now uses Fibre Channel for standard Microsoft Corp. Windows NT platform interconnects.
"That's our first major Fibre Channel deployment, and we'll have to see how that goes, but I'm not contemplating any problems with the use of Fibre Channel in SANs," Conklin said. "As far as it working with [our installed base of peripherals], we've had fibre arrays hooked up with SCSI devices for some time. And from our experience with that, I don't expect major problems."
The Patent and Trademark Office also does not have SANs deployed now but is looking to them "as a strategic way to migrate our computer facility in 2003," according to Larry Cogut, director of PTO's office of system architecture and engineering. However, how much SANs are used within PTO will depend on how well products interoperate within the Fibre Channel loop. Much of the work in this area remains to be done.
The history of battles over SCSI, Ethernet and LAN standards might point to problems ahead for Fibre Channel. Because most of the developers involved with Fibre Channel also suffered through the earlier standards skirmishes, lessons have been learned and Fibre Channel standards "are coming together much faster than other standards have in the past," said Rich Lautzenheiser, strategic marketing manager at Agilent Technologies, a Hewlett-Packard Co. spin-off.
Cogut, however, said he thinks the standards process has been "painfully slow" and that even when standards are hammered out, their eventual market acceptance will be uncertain. If there is any problem with Fibre Channel-based SANs, he said, it lies in the slow pace of the standards process.
Robinson is a free-lance journalist based in Portland, Ore. He can be reached at email@example.com.
What is Fibre Channel?
Fibre Channel is an American National Standards Institute (ANSI) standard that enables gigabits/sec connectivity. It is also used as the basis for the physical foundation layer specification of Gigabit Ethernet. However, unlike Ethernet, which is a networking protocol geared for message-based traffic, Fibre Channel is designed to move large blocks of data in groups.
The Fibre Channel specification describes three network topologies in which it can be used: point-to-point or arbitrated loops for smaller implementations, and in a switched fabric for enterprise-scale environments.
Upstart challenges Fibre Channel
A possible challenge to Fibre Channel could come from the emerging System I/O (SIO) standard, a combination of two previously proposed connectivity architectures called Future I/O and Next Generation I/O.
SIO - which is being backed by leading companies such Compaq Computer Corp., Dell Computer Corp., Hewlett-Packard Co., IBM Corp., Intel Corp., Microsoft Corp. and Sun Microsystems Inc. - could provide interoperable links with aggregate bandwidths ranging from 500 megabytes/sec to 6 gigabytes/sec.
A major potential advantage of SIO compared with Fibre Channel is that it offers backward compatibility with older I/O technologies, promising easier connectivity than the bridges and adapters needed with Fibre Channel, as well as a compatible upgrade path for higher performance interconnect products.
How well this will come together is unclear. Most industry participants are cautious, particularly given the immediate demand for fast SAN interconnections.
"The goal behind both Future I/O and Next Generation I/O was to come up with a channel to move more data between servers and hosts," said Aloke Guha, vice president and chief architect for Storage Technology Inc. "There are plans also to provide switched links to various forms of storage, and in theory SIO could provide much lower cost links than Fibre Channel."
However, it will take time to prove itself in the marketplace. Tom Lassen, senior product manager for EMC Corp. said it could take as long as five years for the SIO group to produce a stable standard. "SCSI has lived its life, and people need to do something now [about their storage]," he said.
It will be several years before the first SIO products are ready, said Rich Lautzenheiser, strategic marketing manager for Agilent Technologies, and even then it will never completely replace Fibre Channel. "There'll be a sizable installed base of Fibre Channel by then, and we are already seeing a move downwards in the cost curve for Fibre Channel," he said.
The first version of the SIO specification could be available by early next year.
- Brian Robinson