FC RAID controllers making headway

Posted on July 01, 1999

RssImageAltText

FC RAID controllers making headway

Fibre Channel RAID controllers come in many flavors, including "full" Fibre Channel and SCSI/Fibre Channel hybrids.

John Haystead

There`s no longer any dispute that, although Fibre Channel technology continues to mature and gain in popularity, SCSI remains strong. Improvements in SCSI performance are providing users with a steady storage upgrade pace, without precluding them from Fibre Channel implementation.

"Fibre Channel is giving new life to SCSI. With the variety of Fibre Channel and mixed FC-SCSI RAID controllers out there, users can integrate Fibre Channel as their needs warrant," says Bob Mohs, technical marketing manager at Distributed Processing Technology (DPT).

The most apparent impact on the Fibre Channel market is a slowdown in the transition to "full" Fibre Channel RAID systems and controllers (e.g., including Fibre Channel at both the host and disk-drive levels). Although Fibre Channel`s superior performance was initially expected to rapidly drive its adoption in RAID systems, as pointed out by Tom Rauscher, president of Digi-Data, "It hasn`t happened. Some of the early Fibre Channel RAID controllers have really been just SCSI controllers with a Fibre Channel front-end, and they haven`t made much difference in terms of performance versus SCSI."

Keith Baskin, vice president of U.S. sales at OneOfUs, agrees: "Fibre Channel advantages just aren`t there in certain situations when you can buy a Fibre-to-LVD SCSI solution that can give you similar performance." In particular, Baskin points out that all Fibre Channel controller vendors face the same issues on RAID-5 write operations. "Fibre Channel far outperforms SCSI on read operations, but it will take a breakthrough for Fibre Channel to compete with LVD SCSI on RAID-5 writes."

So, while some Fibre Channel-to-Fibre Channel RAID controllers are already available, independent controller vendors are rethinking the timing of future introductions. For example, Chaparral Technologies will soon announce a full Fibre Channel-to-Fibre Channel product that may be available by year-end, but the company will first bring out a Fibre Channel-to-Ultra3 SCSI controller.

"We see a higher demand for this product. Several vendors have announced 18GB and 36GB Ultra3 SCSI disk drives operating at 160MBps, and we don`t really see a volume demand for full Fibre Channel developing until next year," says Mike Gluck, president and COO at Chaparral.

Still, most observers agree that Fibre Channel will eventually eclipse SCSI in performance. As noted by Baskin, "SCSI developers are really pushing its electrical limitations and you have to wonder how much more performance can be squeezed out." Meanwhile, Fibre Channel continues to advance with the emergence of 200MBps controller chips and the arrival of full-duplex Fibre Channel drives that will allow RAID controllers to take full advantage of their dual-loop capabilities.

In some ways, however, the promise of future improvements only serves to further encourage vendors to hedge their bets in introducing full Fibre Channel controllers. For example, Gluck says Chaparral may opt to delay its full Fibre Channel product announcement for a quarter in order to move directly to 200MBps Fibre Channel technology.

Nevertheless, the prognosis is still rosy for Fibre Channel over the long haul. For one, although SCSI is keeping pace with the performance of Fibre Channel in some situations, Fibre Channel still offers other advantages that SCSI can`t match--benefits that track directly with the requirements of storage area networks (SANs).

The road to SANs

"SANs will continue to drive the Fibre Channel market and will really take off when concerns over Y2K problems are resolved," says Gluck. Observing that almost every system vendor has announced both Fibre Channel attachment to their hosts as well as a SAN initiative, Gluck predicts the market will see some pilot SAN installations this year, with full production environments ramping up next year.

At the same time, the move to SANs will place obstacles in the path of SCSI-based systems. "We`re finding that people already involved with complex systems are looking for end-to-end fibre solutions," says Bill Bedford, vice president of marketing at Raidtec. "As systems become more complex, SCSI systems become more cumbersome--and before long, prohibitive." DPT`s Mohs agrees: "With SANs, it`s clearly a connectivity and cabling issue. Wherever you need to attach large amounts of storage to networks and servers or need a lot of flexibility, Fibre Channel will shine."

However, major SAN issues remain to be addressed, many of which are clearly highlighted in the current state of Fibre Channel RAID controllers. For example, performance limitations still pose a problem. As pointed out by Digi-Data`s Rauscher, "We can`t even solve the SAN problems we have today. For example, when you connect an active/active RAID system to 100MBps FC-AL, the loop is actually a bottleneck. To get around this you can buy a switch, which is expensive, or you can use a multi-port hub configured as dual FC-ALs." Although Rauscher notes that 200MBps Fibre Channel chips will address this issue in the short run, continuing improvements in host and network performance will eventually cause the bottleneck to reoccur.

Network management

Fibre Channel RAID controller vendors also recognize a need for standardized management software before fully functional SANs can be implemented. As observed by OneOfUs`s Baskin, "SAN management tools are one of the missing pieces for Fibre Channel, and until the technology gets to the point where it can provide file and record-level locking, as opposed to volume-level, Fibre Channel SANs won`t really take off."

Chaparral`s Gluck says that lack of industry standards has slowed the implementation of SANs and Fibre Channel. "Future Fibre Channel RAID controllers will need be to be much more SAN friendly, and while a number of companies are proposing solutions, there are currently no industry-standard protocols. They`re still in the process of being defined."

In addition to individual vendor initiatives, SAN management is also one of the tasks being undertaken by the Storage Networking Industry Association (www.snia.com), which is rapidly becoming a de facto forum for vendors to address standards issues such as the implementation of public fabric support and worldwide names.

Interoperability poses challenges

With the dependence of Fibre Channel on SAN progress, product interoperability and compatibility are particularly critical issues for developers of RAID controllers. The conventional wisdom is that the path to SANs must pass through Fibre Channel switches and hubs, and though most SANs today are based on hubs as opposed to more expensive switches, switch shipments are expected to grow rapidly next year.

As noted by Digi-Data`s Rauscher, "Most people started with hubs in order to have an incremental path for implementing large SANs, but as they grow their systems, there will be more of a balance between hubs and switches." Chaparral`s Gluck agrees: "Switches are coming down in price and people want to have the capabilities they provide for dynamically manipulating their data."

Switch and hub interoperability issues have commanded an inordinate amount of attention from Fibre Channel RAID controller vendors. As observed by Eric Herzog, vice president of marketing at Mylex Corp., "We recognize that we`re just one building block in the overall solution and our OEMs could buy any vendor`s hub or switch."

Likewise, DPT`s Mohs says that "interoperability with hubs and switches is crucial to scaling and to implementing large storage systems. We have to be compatible to prevent being locked out of the business."

The interoperability challenge is significant. As described by Roger Klein, vice president of marketing at CMD Technology, "We`re effectively taking on higher-level OEM-integrator responsibilities for qualifying adapters, enclosures, disk drives, hubs, etc. to allay concerns about interoperability."

To meet the interoperability requirements of different Fibre Channel hubs and switches, controller vendors are incurring additional design and hardware costs. "We`re basically faced with either adding a lot of firmware to our products to make them work with everything, or adding specific firmware for specific switches," says OneOfUs`s Baskin.

Despite the attention, however, Fibre Channel still has a long way to go before it reaches the compatibility level enjoyed by SCSI users. "Unlike the SCSI market where interoperability problems are the exception rather than the rule, they`re still pretty much expected at this stage of the Fibre Channel industry`s development, although it`s improving," says CMD`s Klein.

While continuing to address interoperability problems through vendor partnerships and co-development efforts with system OEMs, Fibre Channel RAID controller vendors ultimately hope for a significant breakthrough--either via industry standards by groups such as SNIA or the appearance of a white knight in the form of a marketing/technology approach that becomes a de facto standard.

It`s an OEM world

Similar to the situation with other Fibre Channel devices, the principal market path today for Fibre Channel RAID controllers is through OEMs. According to Mylex`s Herzog, the primary reason for this is the complexity of Fibre Channel and the continuing perception of interoperability/compatibility issues. "The safe approach is to get Fibre Channel from an OEM who`s providing a complete solution," says Herzog.

As pointed out by OneOfUs`s Baskin, "At this point, Fibre Channel is still far from plug-and-play. You have to have some technical knowledge, and like any new technology, there`s not a lot of people that know how to implement it."

CMD`s Klein agrees: "VARS and resellers tend not to be early adopters of technology because they don`t have the infrastructure or internal expertise to deal with the complexities and problems. But as we go forward, you`ll start to see more responsibility being born by the channel, such as second-tier OEMs and high-end integrators."

A key difference between RAID controllers and other segments of the Fibre Channel market is that Fibre Channel RAID controllers are for the most part first-generation technology, while other segments such as HBAs are already on their second- or third-generation products," says Digi-Data`s Rauscher.

One reason for this appears to be a lag on the part of system OEMs to aggressively push Fibre Channel into the RAID marketplace.

"Internal Fibre Channel controllers have a special attraction for some OEMs and VARs who want to create Fibre Channel server products, but complete system level OEM interest hasn`t really gotten to Fibre Channel yet," notes DPT`s Mohs.

Ultimately, anticipating the eventual widespread acceptance of full Fibre Channel in the RAID market is "like standing on the edge of the diving board. It`s definitely going to happen, the only question is when. Users want it, but we can`t give them everything they need right now," says OneOfUs`s Baskin. As a result, Fibre Channel in the end may capture the RAID storage market more at the slow, steady pace of a marathon swimmer than as a crowd-drenching "cannonball."

Fibre Channel controllers proliferate

The use of an internal or external RAID controller is largely driven by the size and complexity of the application. But today most Fibre Channel RAID controllers are deployed externally with either complete Fibre Channel connectivity to host and drives or a hybrid configuration of Fibre Channel to host and SCSI to drives.

"There are a lot of reasons to go outside the server with Fibre Channel," says Eric Herzog, vice president of marketing at Mylex. For example, external controllers are more scalable than internal devices, simplifying large-scale networking installations by more easily integrating with hubs and switches, or avoiding switches altogether by directly interfacing to hundreds of drives. External controllers are also generally preferable over long host-to-storage distances.

Noting that fault tolerance is a critical criterion for any RAID system, Roger Klein, vice president of marketing at CMD Technology, adds that external controllers allow for more practical implementation of SANs and clusters than PCI-RAID solutions. "PCI doesn`t play very well in the cluster space where, for example, it`s much more difficult to implement cluster failover." Other fault-tolerant design features such as hot-swap, power management, and component redundancy are also generally more difficult to implement in host-based controllers. In the third quarter, CMD will begin deliveries of its Titan CRA-7280 external RAID controller with dual Fibre Channel host interfaces, hot-swappable active/active or active/passive RAID, and eight Ultra2 SCSI disk channels.

On the other hand, internal PCI RAID controllers offer both a cost and space advantage over external devices, providing users with fundamental RAID capabilities without resorting to software-based approaches. Bob Mohs, technical marketing manager at DPT, agrees that external controllers are needed for large SAN environments, but points out that host-based controllers are often preferable for more local applications where they can boost overall host performance.

"Also external controllers are often harder to manage because they`re outside the box, whereas internal controllers have direct access to operating system management tools," says Andreas Koepf, director of support at ICP Vortex.

Though clustering is a little more difficult with internal controllers, Koepf points out that ICP`s Fibre Channel controllers already support Microsoft Cluster Server and the company is working on support for additional clustering environments such as Netware and Linux. In April, ICP began shipping its GDTRN series of 64-Bit PCI-Fibre Channel internal controllers with one or two 100MBps FC-AL channels. The controllers have a standard Wide Ultra SCSI channel equipped with a dual 50/68-pin connector system and active software-switchable termination.

DPT`s Mohs also sees opportunities for PCI-based controllers for clusters. "Many organizations aren`t anxious to throw away their existing investment to implement a SAN. They want to get their foot in the door with clustering." DPT recently introduced the Millennium 3755F internal 64-bit Fibre Channel RAID controller, with one or two FC-AL ports and 16MB of cache. Mohs says the company plans to announce clustering support within the next month, beginning with Windows NT.

Genroco`s Fibre ChannelP-1032 is a 32-bit, 100MBps internal PCI Fibre Channel controller, but the company`s approach to external Fibre Channel RAID is via the TURBOfibre TBF-864 GSN bridge. Genroco has built GSN OS-bypass bridges to Gigabit Ethernet and Fibre Channel, which allow Fibre Channel SCSI commands to be passed via ST protocol encapsulation over GSN switches. The TBF-864 GSN/Fibre Channel bridge supports up to eight 100MBps Fibre Channel ports.

In April, Chaparral Technologies announced its K7413, a canister-size Fibre Channel-Ultra2 SCSI external RAID controller that plugs into a standard 5.25-inch half-height drive bay. Chaparral claims the three-SCSI-channel unit delivers 90MBps on sequential reads and writes, and up to 10,000 I/Os per second. Noting that ease-of-use is another important criteria for RAID users. Chaparral also plans to offer the K series as an OEM board-level product.

Digi-Data`s Z-9552 is a 5.25-inch full-height dual Fibre Channel-Ultra SCSI RAID controller. The six-channel controller allows up to 90 drives per system. Digi-Data president Tom Rauscher says the company also has plans for a Fibre Channel-Ultra2 SCSI product, which is designed to enhance connectivity rather than performance. "Our six disk channels provide 240MBps, which is already more bandwidth than the dual Fibre Channel on the front end." Rauscher also points to the Z-9552`s redundant control repeaters, which allow each controller to operate independently for full-speed active/active RAID during normal operation.

Meanwhile, full Fibre Channel RAID controllers are beginning to make an appearance. For example, Mylex`s DACFF controller supports four Fibre Channel loops and up to 500 drives. According to Mylex`s Herzog, the DACFF delivers over 140MBps on sustained sequential RAID-5 writes.

Adding to its controller line-up, Raidtec recently introduced an external host-independent FC-FC product. Raidtec is positioning the controller in the channel as part of the company`s complete FibreRAID-HI array system, but it is also available to OEMs as a controller-only product. The controller is enhanced with additional software features, including LUN mapping for multi-host environments.

OneOfUs (headquartered in Taipei, Taiwan) will also be in production with a Fibre Channel-to-Fibre Channel product (the Fibre Channel4400) next month. Keith Baskin, vice president of U.S. sales, points to OneofUs`s implementation of Fibre Channel`s advanced command queuing features. "The industry is already coming up against the limitations of cache RAM, but since we only use caching to store the command queue, this removes concerns about cache coherency and battery backup."

The promise of SANs

- Independent storage connectivity

- Heterogeneous connectivity

- Heterogeneous data sharing

- Improved system availability

- Scalability without compromising access or availability

- Improved storage management

- Cost-efficient remote databae mirroring

- Lower overall total cost of ownership

Source: Dataquest

Click here to enlarge image

John Haystead is a freelance writer in Bucksport, Maine, and a frequent contributor to InfoStor.


Comment and Contribute
(Maximum characters: 1200). You have
characters left.