Interface Innovation Set The Stage For Storage Speed Hikes

A flurry of product announcements and industry politicking last week added to the growing competition between the IBM-sponsored Serial Storage Architecture (SSA) interface and an enhanced version of Fiber Channel also targeting high-speed storage interfaces.

Hewlett-Packard, Quantum and Seagate Technology–three major disk drive makers in the 3.5-inch OEM market–are backing the Fiber Channel Arbitrated Loop. Last week, the three disk drive majors claimed that more of the pieces necessary to support Fiber Channel–originally a networking specification connecting high-end data processing equipment–for disk attachment will soon be in place.

These pieces include interface chips from the likes of HP, QLogic and Applied Micro Circuits Corp.(AMCC). In addition, a core implementing the FC-AL specification is expected to be available from some ASIC suppliers. Moreover, the FC-AL proponents claim that more test equipment–thus far an IBM strong point–will be available from the likes of Peer Protocols, Zadian, and others.

To some degree, the new disk attachment strategy for Fiber Channel will be able to garner support from other developments. Targeting a different topology, Sun Microsystems Computer Company (SMCC) last week signed an agreement with Ancor Communications Inc. to jointly develop a switched Fibre Channel attachment to disk storage arrays.

The SSA camp, however, last week also mustered its troops. Micropolis Corp., for example, said that it will demonstrate its Capricorn 4 SSA, a 3.5-inch, 4.3GB drive at CeBIT next month. Also at CeBIT in Hannover, Germany in March, Pathlight Technology will demonstrate its StreamLine-Sbus SSA adapters connecting to Sun workstations.

Micropolis–which is currently experiencing some difficulties, said the Capricorn 4 Model 3243S will be in volume production in Q2. The trio of HP, Quantum and Seagate account for a big chunk of the high-end OEM market and have claimed that IBM’S efforts would be hampered by the lack of a second disk drive maker sourcing SSA components.

Dell Computer Corp., which is seeking to grow in the server market, last week also chimed in with support for the SSA interface. SSA, a dual-ported architecture, is expected to support 80MB/s data transfer speeds. According to Dell, SSA technology will allow up to 127 devices–such as hard drives, tape back-up devices, CD-ROMs and other peripherals–to connect to a single storage controller channel. Devices may be up to 20 meters apart.

Thus far, about 20 companies have joined the SSA Industry Association, whose officers currently come from IBM, Adaptec, Pathlight and Dell. Other member of the SSA group include Conner, Fujitsu, Future Domain, Molex, NCR, Peer Protocols, Silicon Systems, Siemens Nixdorf Informationssysteme, VLSI Technology, Xyratex, and Zadian Technologies.

IBM, though, has clearly been the driving force. In addition to its own silicon efforts, IBM has been partnering for SSA devices with ASIC supplier VLSI Technology. IBM is licensing SSa-related patents for a onetime charge of $5,000 as well as making available test equipment. Another factor is IBM’s growing role in the disk drive OEM market.

Both SSA and FC-AL are being positioned as replacements for older parallel interfaces such as SCSI and will reduce the number of controller cards needed to support disk arrays and peripheral devices. SCSI, however, is also being improved upon and 40MB/s speeds are now possible with Ultra SCSI. Quantum, Adaptec, Bus Logic and Q-Logic are supporting Ultra SCSI.

According to the Fibre Channel group, 3.5-inch disk drives in the 2GB to 10GB range will be targeted with their new serial interface. Seagate has already introduced an FC-AL capable drive.

The FC-AL interface will support up to 200MB/s speeds in a dial-ported architecture; however, it also supports single-port configurations. Distances of up to 30 meters (using copper) are supported with connectivity for 128 devices. A single connector now provides hot-plugging capability.

While the companies behind FC-AL carry considerable industry weight in the disk drive OEM market (Conner is expected to support both SSA and FC-AL), they may be able to leverage support from original Fiber Channel backers. Michael Altree, HP R&D section manager, disk memory division, said that the group is also targeting networked attached storage–with multiple disk arrays connecting to a Fiber Channel backbone–for applications such as video servers.

In other scenarios, remote disk drives could also be supported by a combination of fiber optic backbones–part of the original Fiber Channel standard–and twisted-pair cabling. However, some progress on transmitter/receiver chips for Fiber Channel implementations also needs to be made, said Mr. Altree.

Thus far, these devices have been implemented in gallium arsenide by the likes of Tri-Quint and Vitesse; however, CMOS-based chips are also soon expected. LSI Logic has been active in Fiber Channel, and could be a candidate for upcoming port chips or transmitter/receiver devices. In addition, while Motorola has an implementation for a loop resiliency circuit (LRC) supporting FC-AL–which allows damaged or disconnected drives to be by-passed–another company is also expected to soon provide the capability in silicon.

Dave Anderson, Seagate product planning manager, said that despite SSA’s momentum, FC-AL based products will win out in the long run. In addition to overall cost per node, the serial interfaces are competing in design complexity.

Both SSA and FC-AL use dual-port configurations to support fault tolerance. FC-AL, though, uses an absolute addressing as well as LRC circuitry to aid in hot plug-ability.

SSA also targets a high degree of fault tolerance via multiple layers of error checking and redundancy. SSA includes a capability called “spatial reuse” to send data concurrently between many pairs of serially connected peripherals, without the need to route the data through the processor.

According to SSA advocates, the serial interface is suitable for use in devices intended for attachment to processors that cover the spectrum from mainframes to PCs.

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