The Future of SCSI

Note: See page 3 for Ultra3/Ultra160 overview

Q. What is the future for SCSI beyond today’s products?

A. SCSI has a positive future reflected by the fact that member companies of the SCSI Trade Association adopted a SCSI roadmap outlining future generations following today’s Ultra160 SCSI generation. Ultra320 SCSI, with performance up to 320 MBytes/second and Ultra640 SCSI, with performance up to 640 MBytes/second have been defined, plus additional generations have been targeted. This will give OEMs, resellers and users the bandwidth to accommodate increasingly faster and larger drives, faster CPUs and faster networks. It’s anticipated that products supporting Ultra320 SCSI will begin shipping in 2001, and as with all SCSI products will be compatible with previous generations of SCSI.

Q. Performance is fine, but what about manageability and usability? SCSI traditionally has had an ease-of-use benefit.

A. New SCSI technology will be engineered to provide even more usability and manageability features, including self-tests for ensuring cabling integrity, arbitration to select the optimal data transfer speed supported in the system and error correction. More importantly, future SCSI products will continue to be backward AND forward compatible with previous-generation SCSI devices.

Q. What other improvements are you planning for SCSI?

A. We plan to help standardize the physical enclosures and to continue developing switches, expanders, hubs, extenders and bridges to extend SCSI. We also have agreed to improve desktop connectivity for those higher-end systems requiring multiple peripherals, such as CD-ROMs, scanners, printers, DVD drives, tape back-up and others. Improvements will include devices supporting hot plug capability, providing a 16-bit bus and providing error checking to ensure data integrity.

Q. What technologies are available NOW to improve SCSI?

A. SCSI technology developments include Very High Density Cable Interconnect (VHDCI), LUN bridging and SCSI switching, which allows more devices, up to 960, in the protocol. Both individually and combined, these enable SCSI to go faster and farther. For example, with LUN bridges, 960 devices can be connected, while expanders allow SCSI cables to extend up to 75 meters.

Q. What is the role of SCSI given the availability of USB and 1394?

A. We believe SCSI will continue to be the interface for high-performance systems where multiple devices are connected such as in the enterprise. USB is becoming increasingly available as a connection for printers and mice, for example, but is not typically used for the same applications as SCSI. Today, SCSI is preferred where performance is critical such as on the desktop. The 1394 interface might have a role in some applications, but its market has not developed to the extent that SCSI’s has and its performance might not meet user needs in the high-performance desktop segment.

Q. On the desktop, there are alternatives to SCSI, such as UltraDMA. What is the STA’s position on that issue?

A. We believe that SCSI is well suited for high-performance desktops with multiple devices that need to be connected. As many power users continue to add peripherals to their systems, SCSI is a good choice because it allows for easy connectivity to multiple peripherals and extended cable lengths. In contrast, with UltraDMA, users begin to run out of addresses for their peripherals. SCSI may not be the best fit for lower-performance, low-cost desktops with a single–or just a few–peripherals.

Q. What about Fibre Channel? Many industry analysts report that FC will overtake SCSI in the market.

A. Fibre Channel certainly has a role in the enterprise and that role is long-distance connectivity (such as several kilometers) and connecting multiple systems. SCSI will continue to be the I/O choice for inside the box connectivity for some time to come.

Q. What happens to SCSI with the implementation of the InfiniBand interface? A. SCSI is recognized by proposed system-level interconnects, such as InfiniBand, as an important enabling infrastructure. This inclusion and support for SCSI validates the significance of SCSI in the server market, not only today but also in the future. Higher-performance SCSI devices based on the Ultra2 SCSI specification have become the standard for servers, and new devices based on the Ultra160 SCSI specification are rapidly becoming available.

Ultra3 SCSI/Ultra160 SCSI Overview

Q. What is Ultra3 SCSI?

A. Ultra3 SCSI contains any of five features: double edge clocking, cyclical redundancy checking and domain validation, and manufacturers may also include packetization and/or QAS (Quick Arbitration and Select). These features improve speed, up to 160 MBytes/second, performance and overall manageability of SCSI.

NOTE: for a description of the foregoing features, see the Addendum at the end of the FAQ.

Q. What is the difference between Ultra3 SCSI and Ultra160 SCSI? Both terms are being used in the market.

A. Ultra160 SCSI products are the current generation of performance and manageability and include double edge clocking, cyclical redundancy checking and domain validation. Manufacturers may also include packetization and/or QAS (Quick Arbitration and Select), the same as Ultra3.

Ultra3 and Ultra160 SCSI devices are compatible with one another and with previous generations of SCSI devices.

Q. Are all Ultra3 SCSI products interoperable with one another and with existing Ultra2 SCSI and other SCSI products?

A. Yes, products that incorporate Ultra3 SCSI functionality are interoperable with Ultra2, Ultra160 and with all other SCSI products. This forward and backward compatibility has been a cornerstone of SCSI in the past, and we anticipate that SCSI vendors will continue to ensure investment protection for their customers.

Q. How much additional bandwidth and/or performance does Ultra3 SCSI provide?

A. Customers will receive as much as double the speed over Ultra2 with Ultra3 SCSI, up to 160 MBytes/second. The features of Ultra3 will result in higher performance products with more manageability.

Q. Where can I find Ultra3 SCSI products?

A. A number of vendors today are shipping components, hard drives, connectors and other products. Products are being announced weekly. For a more complete list, check the STA Product List on the STA web site, at http://www.scsita.org under SCSI products.

Q. How will the STA ensure that member and non-member products are compatible?

A. The SCSI standards organization. T10, works to ensure that features are architected for interoperability, no matter what company produces the product. The organization has an established track record of moving SCSI forward into new features and technologies, while maintaining compatibility with existing implementations. Member companies have a strong interest in maintaining compatibility among their product versions. Non-member companies are motivated to comply with the standards in order to sell their SCSI products.

General SCSI

Q. What role does SCSI play in storage area networking (SAN) configurations?

A. There are many stable, reliable and high-performance SCSI devices from a variety of vendors for storage area networking. The STA’s position is that SCSI will continue to have a strong presence in server interconnect, host connect and interconnect, subsystems and peripherals. For more information on the role of SCSI in the SAN, see the September 1999 slide presentation, "SCSI and SANs," located on the STA web site, at http://www.scsita.org under News and Events.

Q. SCSI has been questioned as having limitations on distance and speed. Why should anyone buy a SCSI-based product?

A. The performance of SCSI-based products has frequently been better than the performance of products based on other interfaces in industry benchmark tests. Today’s SCSI products can connect devices up to 12 meters. With LUN bridges and switched SCSI technology, for example, SCSI can connect 960 devices per bus, and with expanders, extend the cable length up to 75 meters. Servers and high-end systems have multiple buses allowing thousands of drives per system. RAID systems allow connection of hundreds of drives to a single port, since the RAID box appears as a single drive to the system.

Q. Bottom line, what are the greatest advantages for an IT manager to continue implementing SCSI?

A. The greatest advantages in implementing SCSI are performance, manageability and investment protection. In addition, the ability to quickly add devices and integrate them into the IT environment is a critical consideration, while the proven effectiveness of SCSI technology helps ensure that devices work as they should, even as other SCSI devices are added or subtracted. Finally, because suppliers continue to develop and manufacture products based on various versions of SCSI, users are ensured a wide variety of choices for their devices.

SCSI Trade Association

Q. What is the SCSI Trade Association?

A. The SCSI Trade Association, or STA, was formed in 1995 to promote the use and understanding of small computer system parallel interface technology, to provide a focal point for communicating SCSI benefits, and to influence the evolution of SCSI in the future. The STA is headquartered at 404 Balboa St., San Francisco, CA 94118, telephone (415) 750-8351. Additional information is available at http://www.scsita.org, or by contacting the STA at info@scsita.org.

A. STA member companies represent every segment of computing, from hard drives to peripherals to components. A complete list of member companies is available on the STA web site, http://www.scsita.org.