Server/Storage Networking

ENT, March 4, 1998 by Sam Alunni

A new area of computer technology has slowly emerged over the past year. In fact, it is so new that people are still not certain what to call it. Some refer to it as storage-area networking, or SAN, while others call it server/storage networking, or SSN. Regardless of the problems surrounding its name, server/storage networking (my preference) has attracted the key ingredient that should put it on all our radar screens -- money. Over the past year, venture capitalists have poured their dollars into a new crop of startups such as Gadzoox Networks Inc. (San Jose, Calif.), G2 Networks Inc. (Los Gatos, Calif.) and Brocade Communications Inc. (Sunnyvale, Calif.). In addition, well-established companies are also jumping into the business. McDATA, a subsidiary of the storage giant EMC Corp. (Hopkinton, Mass.), and Ancor Communications Inc. (Minneapolis), a Fibre Channel manufacturer, are just two companies that have expanded their business strategies to include server/storage networking products.

Server/storage networking amounts to nothing more than the application of hub and switching technologies to the space between servers and their storage. In effect, the copper cabling between a particular server and a particular piece of storage is replaced by a fiber-optic based network that uses hubs and switches to connect all the servers and all the storage into one large fabric. The result is a server/storage network that is extendible, manageable, durable and fast. Users can extend it to the limits of fiber-optic technology, control it from a standard management platform such as OpenView, equip it with redundant, hot-standby failover capability, and allow it to transfer data to and from storage at gigabit speeds.

The storage/server network's genesis goes back to 1988 when the American National Standards Institute (ANSI) developed the standards for Fibre Channel so that it could be used as a high-performance link for data transfers between mainframes, supercomputers, workstations and peripheral devices. After that, the Fibre Channel Association was formed to work as the champion for Fibre Channel's use in the areas specified by ANSI. Then, with the advent of hubs and switches in traditional networking, equipment manufacturers found the ideal platform concept on which to offer Fibre Channel storage solutions to the widest possible market. Combine all this with the fact that SCSI is scrambling to stay up with predicted storage transfer rates and requirements.

Interestingly, the differences among server/storage products fall into the same categories as the differences between hubs and switches in traditional networking. First, hubs are shared media devices. As more servers and/or storage peripherals are added to a hub, there is an increased chance that the available bandwidth will be in use at any particular moment. Simply put, more devices on a common medium increase the chance that contention for the medium will occur. As a result, a particular data transfer might be forced to wait until the arbitration mechanism rules that it can have access to the Fibre Channel medium. In short, for hubs, more devices means more contention means more waiting means greater latency in the data transfers. The good news, however, is that hubs are relatively inexpensive, compared with switches. And for many of today's application environments, their shared 1-Gbps speed is more than adequate.

Switches are the real workhorses of server/storage networking -- just as in traditional networking. One of the best features of a switch is its port-related scalable bandwidth. This means that as ports are added to a switch, incremental bandwidth is added as well. In McDATA's-4000, for example, users can install up to 32 ports in the chassis. The good news is that when all 32 ports are used, there are 32 gigabits of full-duplex bandwidth available for all the ports to share. The downside of all switches, of course, is price. Expect to pay for all that performance. But then again, your application environment may cost-justify the use of server/storage network switches.

There is another analogy that holds with traditional networking: Hubs and switches can work together in a server/storage network. One of the ports on a hub is used to connect to one of the ports on a switch. As a result, the devices attached to the hub can get access to the devices connected to the switch. And vice versa. There are many benefits related to this capability. One of the most important, of course, is that users can preserve their investment in hubs if their requirements change and they move up to switches.

Don't expect to get sales calls from most of the suppliers I've mentioned. With the exception of McDATA and Ancor, almost all of the smaller companies are using OEM channels to distribute their products in the U.S. If your tape- or disk-drive manufacturer folks start talking to you about server/storage networking, don't forget to ask them whose products they're selling. -- Sam Alunni is vice president of networking at Sterling Research (Sterling, Mass.). Contact him at alunni@sterlingresearch.com.