Imagine if all your storage devices were attached to a switch and could communicate with each other. And imagine all storage administration and management was totally automated. With no need to guide storage and retrieval traffic, manage backups or worry about the performance strain on your network, you could become the Maytag repairman of storage management.
This isn't an impossible dream - it's all part of the promise of storage-area networks (SAN). A SAN is a collection of networked storage devices, such as server hard drives, tape libraries, RAID and CD jukeboxes, which are able to communicate with each other automatically.
The automated management software required to make SANs a reality isn't yet available. However, the underpinnings of SANs are maturing, providing the technology for some useful, cost-effective applications that you can start using today.
FC-AL: A first step
Robert Kisor, vice president of engineering and technical services at Paramount Pictures in Hollywood, California, recently implemented the Fibre Channel-Arbitrated Loop (FC-AL) transport protocol as the com- pany's first step toward a SAN. FC-AL supports 200M-bit per second (bps) throughput, dual-port channels and hot-pluggable drives. Storage vendors are positioning FC-AL as the leading interface for SANs.
Think of FC-AL as SCSI on steroids. While SCSI can only connect up to 15 devices, FC-AL lets you connect as many as 125 devices to a single host adapter. And while SCSI requires hundreds of wires to attach devices, FC-AL's loop architecture lets you use one cable to create a loop among the attached devices.
Paramount has eight high-end servers and scores of workstations on a FC-AL loop that's used to transfer video for the TV show Entertainment Tonight. The ample throughput allows editors to send video to the production crew for live news feeds and makes the editing process much faster, Kisor says. It used to take a few minutes to pull up video; now it happens in real time.
"We went with Fibre Channel because we had a 15-year-old video editing system in place that was totally inefficient and obsolete," Kisor says. "When I researched the options, FC-AL was easiest to implement and integrate with our existing editing software and production systems."
Ken Hallam, director of technology for storage systems engineering at Unisys in Mission Viejo, California, says FC-AL is attractive because it's a dual-port technology, just like SCSI. This means a server can simultaneously send and retrieve documents to the same tape drive with no waiting.
FC-AL is also built for distance, which is useful in an environment such as Unisys' in which tape libraries are scattered throughout the building. "I don't need to buy repeaters to cover the distance down the hall to our tape library room like I do with SCSI," Hallam says. While SCSI only allows a 25-meter stretch between machines, FC-AL supports spans of up to 10 km.
Moreover, FC-AL is less expensive to implement than SCSI. FC-AL host adapters cost between US$700 and $1,200; SCSI adapters only cost about $150, but you need to buy one SCSI adapter for every seven to 15 drives, Hallam says. And because FC-AL requires fewer adapters, there's less maintenance and upkeep.
Hallam has been working with FC-AL for about two years, and says one of the most striking differences between it and SCSI is network availability during daily backups. Backups used to push the network to its limit and usually took the entire night. During a backup, many telecommuters were unable to log on because the network was so bogged down.
Now that the SAN routes backup traffic for the best performance, "It takes about one hour, and even during that hour, accessing the network is no problem," Hallam says. "Telecommuters can be a lot more productive."
The implementation itself was a no-brainer, Hallam adds. "Everything gets wired into the backplane of the circuit board with very few software changes."
However, interoperability must be considered when choosing a SAN. "Pay attention to the details and compatibility with existing systems, and you won't have much trouble," Kisor says. "We chose Tektronix because it integrated well with our editing software."
Although companies such as Paramount and Unisys are already reaping the benefits of FC-AL, it will be some time before they'll be able to fully realize the benefit of SANs. Several limitations of Fibre Channel technology are holding back the development of automated SANs.
Instead of relying on the loop architecture, full Fibre Channel implementations use switches to route traffic - this requires a major software overhaul. Two years into Unisys' deployment, "We're still working on rewriting the software code in order to make switching work," Hallam says. "It's expensive and laborious and requires a lot of expertise."
The key problem Unisys has encountered is with the drivers. "There are big software changes as soon as you start spreading out availability of different storage devices," he says, noting that a switched network might include as many as 16 million disk drives. Hallam's engineers are working closely with Unisys' primary Fibre Channel vendor, Seagate, to share the programming work. He expects to finish later this year.
Moreover, while Fibre Channel provides more centralized management, servers don't automatically route data where it belongs. The instructions must still come from the multiple host adapters, and the management software to automate those instructions needs to be improved.
"I'm keeping an eye on management software and watching as it evolves," Hallam says. "There still has to be an administrator monitoring our network. I hope to achieve full automation at some point, maybe within a few years."
Kisor has made no move to fully switched Fibre Channel yet, and probably won't until the automated management is worked out.
Tom Lahive, senior storage systems analyst at market researcher Dataquest in San Jose, says interoperability, reliable chip sets and compatibility with Windows NT are other thorny issues that need to be addressed before switched Fibre Channel is ready for prime time. "One vendor's device doesn't necessarily work with another's, and you can't ignore incompatibility with a platform like NT," he says. Today's SANs support Unix.
Not surprisingly, vendors are singing a slightly different tune. Most host bus manufacturers are developing the enabling drivers for Fibre Channel-ready switches, says Peter Tarrant, vice president of marketing and systems development for Fibre Channel switch manufacturer Brocade in San Jose.
Tarrant says NT compatibility will exist soon, and companies such as Compaq and StorageTek are integrating drivers into Fibre Channel network devices such as hubs and switches.
Even though the driver issue isn't solved, Tarrant argues that switched Fibre Channel is so superior to FC-AL that it's worth the implementation hassles. "The real issue of switches versus the hub loop is that the loop is not reliable. When the loop fails, the whole thing goes down," he says. "With the switch approach, there is fault tolerance."
However, Hallam points out that hot-pluggable drives allow administrators to replace a failed drive without bringing the whole looped network down.
Besides, vendors such as Ancor, Brocade and Vixel are pricing their Fibre Channel switches at $17,000 and up. When you're spending that kind of money, the programming costs associated with switched Fibre Channel won't look so expensive.
"Nothing is easy, and Fibre Channel is no exception," says Nick Allen, vice president and research director of Gartner Group in Stamford, Connecticut. "It is, however, a viable mechanism, and despite its glitches, it's the only candidate out there."
Companies with extensive testing capabilities have the best chance of success with Fibre Channel switching rollouts. If you're thinking of becoming an early adopter, consider buying all your Fibre Channel products from the same vendor because the technology is hard to debug and troubleshoot. "People tend to forget that new technologies just take time to work themselves out," Allen says.