Here's a piece that has Craig Frane making quotes;
Serial SCSI Buses: New Technologies
Hard drives were once the speed bottlenecks, but even Fast and Wide SCSI interfaces won't be speedy enough to handle RAID systems built with the next generation of high-capacity drives.
Seagate's 4.5GB to 9GB Barracuda 3.5-inch drives, for example, boast data transfer rates approaching 10MBps. And drive manufacturers are improving performance some 30 to 50 percent every 15 to 18 months, according to Craig Frane, Seagate's director of marketing and planning. Link a couple of these drives together, he says, and you're going to need a faster interface.
In the short run, Seagate--and most of the storage industry--is addressing the speed shortage by doubling the SCSI's internal clock speed. With the new UltraSCSI protocol (which the American National Standards Institute committee calls Fast-20 and Fast-40), Fast SCSI-2 offers 20MBps, and Fast and Wide SCSI-2 provides 40MBps. In fact, Conner, Hewlett-Packard, Micropolis and Seagate (among others) are all planning drives that use the new UltraSCSI standard, and some RAID integrators (like ProMax) are offering UltraSCSI-ready controllers as part of their RAID bundles. (UltraSCSI is backward-compatible with existing SCSI hardware.)
Some experts warn that UltraSCSI is likely to cause cabling headaches. "The speed increase halves [the maximum] SCSI cable length to about 10 feet," says Dennis Hoffman, storage manager for Avid Technology. "That makes it almost impossible to get seven drives on a bus. People on the desktop will end up running into problems because so much will depend on the quality of connectors. We will probably avoid it."
Fibre Channel vs. SSA
Instead, Hoffman is betting that drives and controllers based on two new rival standards--SSA (Serial Storage Architecture) and FC-AL (Fibre Channel Arbitrated Loop)--will arrive soon enough to solve his speed and cabling problems.
The 100MBps FC-AL standard--which is supported by a consortium of 35 manufacturers--is a favorite. Symbios Logic offers a Fibre Channel RAID 0, 1, 3 and 5 controller and a PCI-Fibre Channel SCSI adapter with a 100MBps burst rate and a 45MBps sustained transfer rate. However, end users won't see the products until mid-'96, and initially they will carry a 50 percent price premium over comparable SCSI products, says Ron Engelbrecht, director of Symbios Logic's OEM RAID unit.
Seagate's Barracudas are based on both UltraSCSI and FC-AL interfaces, though the FC-AL models come at a 5 percent price premium, according to Frane.
The 80MBps SSA standard, in contrast, is further along in terms of actual market presence. IBM, which developed the standard and is the biggest drive maker around, has been shipping SSA-based drives, storage subsystems and PCI adapters to OEMs since August 1995. And other companies are following suit: Micropolis and Conner plan SSA drives, Adaptec is working on adapters and Pathlight Technology is shipping an $850 StreamLine-PCI dual-channel SSA half-size board for PCI-bus Macs or PCs. By April, Pathlight Technology plans to ship a companion card with a 1394 connector so that you can hook up Sony's new line of digital video cameras directly to your computer. Another version of the adapter card, the High Speed SSA Data Pump, will let you bypass the computer's PCI bus and record directly onto a RAID array, according to the company.
Although SSA theoretically achieves transfer rates of only 80MBps, it actually performs better than FC-AL's 100 in RAID Level 5 applications and is more cost-effective, according to a report by International Data Corp. (IDC) of Framingham, Massachusetts.
The FireWire Challenge
With Fibre Channel and SSA stealing most of the spotlight, the low-cost IEEE 1394 (Apple's FireWire) interface appears the dark horse. Its viability may depend on the success of consumer products such as Sony's digital camera.
Austin, Texas-based Skipstone is the first to ship to developers a PCI adapter based on the Texas Instruments chipset that lets PCs (and soon Macs) communicate directly with 1394 devices. The TI chipset has been achieving transfer rates of 100Mbps; by press time it should be achieving 200Mbps. And in a year from now, TI's chips should offer 400Mbps, according to Larry Blackledge, the company's 1394 market development manager.
Apple plans to support 1394 in software in 1996 and include the standard in motherboards sometime in 1997, according to Johnathan Zar, Apple's 1394's product manger.
All of these new serial SCSI protocols offer a number of advantages over the old SCSI-2 technology. The 1394 standard, for example, lets you hook up 63 devices; SSA and Fibre Channel allow 126. These new serial buses also support isochronous data transfer, which guarantees that time critical packets of information (like digital video and synchronized audio) arrive at a precise time--the key to a single multimedia bus of the future.
What's missing are hard drives. Because 1394 feeds data isochronously (continuously), it presents new design challenges that drive makers still need to overcome, says Bob Otis, manager of Apple's storage systems group. "They [the drive manufacturers] haven't figured it out yet," he says. "Before they do, they need to know they'll be able to ship drives in volume."
According to Sony and Texas Instruments, both Conner and Seagate are considering building drives based on the standard. However, neither company would confirm this. And without drives and RAID arrays, those wishing to take advantage of the new digital cameras may have to pay for extra adapters.--Jiri Weiss and Bob Doyle |
