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SCSI (Small Computer System Interface) has dominated the storage I/O market for more than 15 years. Its technology roots go back to 1981 when work began on an I/O technology later named SCSI. Since that time it has evolved to keep pace with an exploding computer industry that demands more bandwidth, performance, features, manageability and flexibility each year.
SCSI data rates track those of hard disk drives, doubling every two years and reaching 160 MBps in the current generation Ultra320 SCSI. There have been six generations of SCSI technology to date, with more over the horizon, including Ultra320 and Ultra640. Unlike other I/O interfaces, SCSI product generations are always backward and forward compatible, preserving the user's investment and allowing legacy devices to be connected to newer systems. There are now more than 100 qualified SCSI vendors in the industry providing hardware, software, cables and plug terminators, all of which are interoperable.
SCSI is ideally suited for many applications across the industry, beginning with RAID (Redundant Array of Independent Disks) storage, Internet and enterprise servers, workstations and application-specific computing. Desktop connectivity is vitally important in today's Internet economy and SCSI is meeting the challenge. It is the most cost-effective high-end disk drive controller interface on the market today.
Roger Cox, Chief Analyst, GartnerGroup/Dataquest, projects that the unit volume of host-based SCSI RAID controllers will double from 1999 to 2003.
In another GartnerGroup/Dataquest study, Adam Couture, Senior Analyst, IT Services, evaluated the storage utility market. He projects that the storage utility market will grow from $10 million in 2000 to $8 billion in 2003, 75% of which ($6 billion) will be generated by Internet data centers.
Storage utilities deliver capacity for servers on a usage basis, capacity that may be delivered via user networks or the Internet. Dataquest's projection that $6 billion will be Internet related suggests to STA that a significant proportion of the $6 billion could contain SCSI technology. SCSI technology would most likely be inside the servers, which are connected to the storage utilities via SCSI or Fibre channel protocols. Currently, SCSI is used in a high percentage of RAID controllers and that will likely continue for some time. By STA estimates, close to 95% of all servers supporting the Internet rely on SCSI I/O technology.
By 2003, STA projects that the hard disk drive media rate will be 90 MBps and the required bus bandwidth will be 360 MBps. In 2003, the Ultra640 SCSI generation will be entering the market. The future of SCSI, as a widely-used storage controller technology, is secure due to the extensive worldwide installed base and the ongoing performance improvements in each generation of the specification.
SCSI is superior to all other bus options as the highest performer with the least CPU loading of any interface on the market. When performance really counts in transferring data from a disk, scanner, removable media, etc., SCSI is the fastest.
Ultra320 (also known as Ultra3), the current generation of SCSI technology, provides speeds up to 160 MBps. In addition, low voltage differential (LVD) drivers, double transition clocks (DT), domain validation (DV), cyclic redundancy check (CRC), quick arbitrate and select (QAS) and packetized protocol, have all markedly improved performance, as has high-speed host-to-host connection.
SCSI I/O technology is highly suited to enterprise computing, the entertainment industry (including video editing and transaction processing), storage area networks (SAN), clustered computing and Internet applications. The SCSI standard accommodates storage disks, tape, CD drives, printers and scanners, allowing these devices to be easily moved from system to system for backup or resource sharing.
Currently, SCSI cables can reach up to 25 meters for point-to-point applications and up to 12 meters for multi-point applications. For more sophisticated implementations, cables with expanders can reach up to 75 meters and will support up to 1000 devices with the near-term introduction of LUN (Logical Unit Number) bridges. A multi-drop parallel bus has the ability to support devices at different speeds on the same bus.
Today, SCSI connectivity is easy. Virtually every peripheral type is recognized by the SCSI standard, taking advantage of the newest hardware and the most intelligent controllers available. Peripherals used on the desktop connect and disconnect instantly and transparently, taking advantage of auto termination and plug and play. Improvements in the technology have led to more flexible cables and dramatically reduced connector sizes. SCSI allows connectivity inside and outside the box with up to seven devices on a narrow bus and 15 on a wide bus, plus the controller.
SCSI is a stable, proven I/O solution that outperforms other I/O technologies. It is more cost-effective than Fibre Channel. Today, SCSI is the technology of choice for the vast majority of server and high-performance PC environments. This is due to the important features of upgradability, scalability, manageability, inter-generational device compatibility, reliability and performance. As SCSI continues to increase in speed and add new features, it promises to remain a viable technology for storage and for desktop connectivity in the long-term.
The market is demanding longer distance connectivity and greater peripheral connection capability as well as dynamic configuration features. Low cost remains an important factor. In addition, new expanders, new extenders and LUN bridges are on the horizon. Another widely demanded feature hot swap. SCSI specification development is currently underway to provide these features within a competitive price range.
Important future SCSI developments will be the increased performance defined by Ultra320 and Ultra640, with additional generations to follow. Planned features for Ultra320 include double edge clocking, packetized protocol and domain validation with signal margining. The Ultra640 specification will include additional enhancements to increase performance and reliability. When the market is ready for new features or performance enhancements, SCSI will provide the total solution, maintaining its position as the I/O technology of choice for future enterprise computing, Internet computing and desktop applications.
Paper reprinted with permission from the STA.
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