The fifteen year-old SCSI I/O interface has a new roadmap that should increase its transfer rates up to 640 Megabytes per second over the next four years, the SCSI Trade Association announced at Winhec show in Los Angeles yesterday. The plan pushes data transfer rates from the current 160Mbps under Ultra3 SCSI up to Ultra 4 SCSI, running at 320MB/sec in less than two years, and then on to 640Mbps Ultra 5 SCSI by 2003. The first versions, in the early 1980s, ran at 1.5Mbps.
Despite much talk of alternatives such as fibre channel, Ultra DMA, USB and Firewire, SCSI still predominates in the server and workstation market – and with SCSI support built into Windows NT, the shift from Unix to Intel and NT isn’t affecting its growth. SCSI is important for power users wanting high-speed access to fast internal drives and external optical drives, and is the most common interface to peripherals from portables and Macs. Some 18.3 million SCSI disk drives shipped in 1998, an average growth rate of 25% over the last two years. Around 95% of high-end disk drives shipped use the interface, according to Dataquest figures.
The STA says its new plan now coincides with the rate of evolution in the disk drive market, which doubles capacity every two years. Performance gains, which started with the new signaling levels of low voltage differential transmission for Ultra SCSI 2, will be achieved through a variety of new techniques, including cyclic redundancy code, which protects data from being lost in the event of poor connections, and dynamic validation, which enables performance to be dynamically turned to the highest rate a system will support. Beyond that bandwidth efficiency are management technologies such as domain validation margining, skew management and self timing circuits are planned. Serial, rather than parallel, versions of SCSI have also been discussed.
At the high-end, the biggest challenge to SCSI is likely to come from fibre channel at the high-end, especially for long distance connections and complex storage area networks where switches and routers are required. At the low-end, where price is the biggest factor, UltraDMA, with its 33Mbps transfer rates, is likely to dominate. USB is gaining strength in the low-bandwidth arena, and Firewire is doing well in its consumer niche. SCSI, the STA insists, has a long life and is continuing to grow. New versions of SCSI will maintain forward and backward compatibility, although there will be subtle changes in the topology that are likely to cause some transitional issues.
Even if other interconnect schemes take off, SCSI is still likely to play a bridging role between peripherals and such technologies as Gigabit Ethernet, Future I/O and NGIO. Currently, the first products from such companies as Adaptec Inc and Quantum Corp are reaching the OEM market, using the Ultra160/m subset of Ultra 3. IBM Corp and Western Digital Corp are due to launch products shortly, with products expected to reach the sales channels by the fourth quarter of the year.
