Fibre Channel Means Business
Here`s a rundown of the key business benefits of Fibre Channel and the applications that are driving its adoption.
By Logan Henriquez
In 1997, the average storage capacity of x86 servers doubled, and this year`s forecast is no less bullish. In business applications, the increasing use of information-sharing applications such as Lotus Notes, email, Web, and data marts is driving storage growth. Another factor is the average file and database size required by these applications--not to mention the ease of adding graphical, animated, and sound content to data files.
For knowledge workers, these are critical applications with stringent up-time requirements. The migration of traditional mission-critical applications from mainframe environments to client/server networks also adds to the data growth and strains the ability of IS staff to deliver mainframe-class availability, management, and backup.
To address these needs, storage vendors are rallying around the Fibre Channel interconnect. Initially, Fibre Channel storage systems will be used where SCSI-based systems are inadequate, while SCSI will continue to be used in many applications. More features, new technology, and lower production volumes will mean higher costs--at least initially--for some of Fibre Channel`s electronics, though an actual apples-to-apples price comparison of SCSI and Fibre Channel isn`t truly possible since many of the new interconnect`s features and components (e.g., optical-electrical converters and hubs) don`t exist in the SCSI market. As volumes increase and prices drop, however, Fibre Channel will become as ubiquitous as SCSI.
What Is Fibre Channel?
Fibre Channel is a next-generation transport mechanism that supports multiple protocols, including SCSI, IP, HIPPI, and IPI. The five layers of the Fibre Channel standard define a physical layer, encode/decode scheme, framing protocol and common services, and channel and network protocols.
Fibre Channel uses the same physical media as Gigabit Ethernet: fiber optic or copper connections. Both Fibre Channel and Gigabit Ethernet offer 100MBps transfer speed. However, the two interconnects require different electronics (they can`t share hubs, switches, or controllers) and have distinctly different applications: Ethernet is designed for communications network; Fibre Channel, for low-latency storage networks.
Fiber-optic connections allow distances of 500 meters with multi-mode fiber and up to 10 kilometers with single-mode fiber. Industry-standard connectors, such as the electro-optic GBIC, enable users to attach devices from different vendors with the same hot-pluggable connector. Thus, storage users are no longer restricted to the 12-foot cable lengths of single-ended SCSI.
Mirrored storage configurations are also possible--and at a lower cost than some of today`s more expensive alternatives. Physical consolidation of storage also becomes easier, even if the servers are located at different corners of a data center or building.
Fibre Channel also supports multiple topologies (e.g., point-to-point, crosspoint-switched, and arbitrated loop), depending on performance requirements, packaging options, and capacity/scalability requirements. At first, storage solutions are expected to implement primarily Fibre Channel-Arbitrated Loop (FC-AL) topologies; switched fabrics will be added as bandwidth requirements increase.
Many FC-AL implementations consist of a loop expansion module or a hub between servers and storage devices, which allows star-cabling configurations while maintaining a logical loop between the connected devices. The FC-AL topology allows users to attach up to 127 devices to a single loop, but actual implementations will involve fewer devices due to slot limitations and performance requirements.
Communication between these devices may occur using any of the supported protocols, but due to the size of the installed base of SCSI storage devices, many implementations will use the SCSI command set on top of the Fibre Channel transport. Disk drives, arrays, tape backup devices, hubs, and switches may be connected to the loop, enabling users to build storage-area networks (SANs)--i.e., high-speed networks of intercommunicating storage devices.
Storage backbones can be distinguished from communications backbones by their protocols. Gigabit Ethernet implementations will continue to use CSMA/CD to arbitrate network usage among clients and will not be optimized for the low-latency, high-reliability requirements of storage. A separate storage backbone means that the communications network is not burdened by storage traffic and vice versa. Instead, each backbone is optimized for its specific purpose.
What Are the Applications?
Fibre Channel is not an application- specific technology. Like SCSI, it covers a wide range of applications. However, Fibre Channel opens up some new possibilities for certain applications. The following discussion focuses on general business applications rather than specialty applications (e.g., video).
High growth/capacity apps--Applications that are driving capacities higher include data marts and data warehouses, group ware (e.g., Lotus Notes), Web servers, email servers, and databases. And then there is the trend at larger companies to consolidate the hundreds of small server platforms distributed in work groups into larger servers deployed in departments or data centers. Even basic file and print servers are affected--the consolidation is driving some companies to build terabyte-size servers that serve thousands of clients.
Fibre-Channel storage systems have clear benefits for such high-capacity applications. While most servers today may not be in the hundreds of gigabytes range, they will be within the life cycle of the server`s storage system. Decision support applications in particular require more scalable storage systems so that multiple versions of analyses can be stored.
"Plan for three times the capacity you think you`ll need." That`s the often quoted rule for rolling out a data mart. Fibre Channel`s connectivity and higher speed enables 3TB+ configurations using six PCI slots and 9GB drives with an industry-standard x86 server, but allows users to start with configurations of under 50GB. The result: a simpler and more cost-effective path to multi- terabyte storage.
Some vendors have circumvented SCSI`s limitations by building large external controllers that have many SCSI connections on the disk-drive side. In these architectures, the controller is the potential bottleneck. Consequently, vendors are engineering large amounts of cache and processing power into the controller, which increases the cost of the total system and results in a higher initial purchase price.
Fibre Channel, on the other hand, does not require a large controller, which allows vendors to use more cost-efficient modular and scalable components. Moreover, Fibre Channel drives do not need to be used, thereby protecting users` investments in SCSI drives.
Clustering--Fibre Channel also improves server connectivity--for the very same reasons that it increases storage connectivity. FC-AL hardware allows users to attach multiple servers to a storage network in high-availability clusters. Server hardware vendors and their software partners are collaborating to integrate solutions.
Right now, vendors are focusing on Fibre Channel storage systems that work with Microsoft`s two-node failover cluster (MSCS, a.k.a. Wolfpack). Fibre Channel`s architecture allows users to attach multiple servers and storage devices to the same loop via a hub or switch.
Transaction environments--In on-line transaction processing (OLTP) environments, disk I/O often determines ultimate system performance. By adding more drive spindles and increasing peripheral processing power, the disk subsystem is no longer a bottleneck.
Fibre Channel allows users to attach more disk drives and storage controllers to single servers or clusters of servers, significantly increasing I/O perfor- mance. And Fibre Channel maximizes peripheral slot usage.
Fibre Channel can be implemented as an interconnect between a server and a storage enclosure or inside the storage enclosure connecting the hard drives. Over the next two years, however, the majority of Fibre Channel-based storage devices are expected to emphasize the server-to- storage interconnect rather than the drive-level interconnect, primarily because the benefits of Fibre Channel can be achieved without using Fibre Channel disk drives. Currently, multiple vendors are manufacturing SCSI disk drives; in contrast, Seagate is the only drive manufacturing currently shipping Fibre Channel drives.
Later this year, more vendors are expected to begin shipping Fibre Channel drives, and the prices of these drives are expected to come down in 1999. At that point, Fibre Channel will become common at the drive level. Fibre Channel disk drives are not compatible with SCSI storage enclosures, and SCSI drives cannot be used with Fibre Channel backplanes and enclosures.
From a technical perspective, Fibre Channel delivers some exciting features: higher transfer speeds, greater connectivity, simpler cabling, and longer distances. From the user perspective, some of the key benefits of building storage backbones with Fibre Channel include:
- The ability to scale storage capacity and performance from a few gigabytes to terabytes without starting from scratch with new equipment.
- High speed backups that transfer data directly between disk and tape over the storage backbone.
- Flexibility to locate your hard-disk subsystems, backup devices, and servers where you want, without giving up the benefits of centralized backup and management.
Applications Driving Demand for Fibre Channel
- Data marts, data warehouses and decision support
- Web servers
- Large databases, including online transaction processing
More information about the Fibre Channel standard is available from the Fibre Channel Association at www.fibre- channel.com and from the Fibre Channel Loop Community at www.fcloop.org.
The five layers of the Fibre Channel standard define a physical layer, encode/ decode scheme, framing protocol and common services, as well as channel and network protocols.
Logan Henriquez is group product manager in Compaq Computer Corp.`s enterprise storage and options division in Houston, TX.