Look Before You Leap To Ultra3 SCSI

New technology doubles bandwidth, but VARs need to be aware of variations in the standard.

As most storage VARs know, Ultra3 SCSI technology is becoming increasingly available. Quantum is currently offering its 18 GB Atlas IV drive, and Mylex has announced an Ultra3 RAID controller. Other vendors, such as Seagate, are also lining up to make the jump into the Ultra3 space.

It's easy to understand why storage vendors are moving to third-generation SCSI technology. According to Mike Joyce, director of channel marketing for Mylex Corporation, there are a number of clear benefits to Ultra3. "The most obvious benefit is the doubling of bandwidth from the second-generation Ultra2 product," he said. "Ultra2 offered an 80 MB-per-second transfer rate. Ultra3 offers a 160 MB-per-second transfer rate. Ultra3 is also backward-compatible with Ultra2, which protects current SCSI investments."

Specification Variance
However, there could be problems hidden within the standard. SCSI - otherwise known as small computer systems interface - is a parallel interface designed to communicate with intelligent peripheral devices. The interface has been standardized by the American National Standards Institute (ANSI).

The term "Ultra3 SCSI" was created by the SCSI Trade Association (STA) to describe any device that combines Ultra2 with one (or more) of six new features, as defined by the ANSI SPI-3 specification. The problem with this specification, however, is that there could be as many as 63 variations that could qualify as Ultra3.

That could mean big problems for VARs. VARs could find themselves in situations where two products labeled "Ultra3" don't share the same features and therefore are not able to communicate at the 160 MB-per-second transfer rate.

According to Johnny Cardosi, VP of worldwide distribution sales and marketing for DPT Corporation of Maitland, FL, the solution is to work with vendors who have tested all the Ultra3 products for compatibility. "Not all the drive manufacturers are on the same page," he said. "For example, Seagate, IBM, and Quantum all implement the Ultra3 specification a little differently. This can be traced back to the original specification, which - in my opinion - should have been tighter. Therefore, if VARs don't want to be caught between specifications, they should work closely with a vendor that has tested Ultra3 products for compatibility."

Cable Length
But wait…there's more. Another concern involving Ultra3 is cable length. Ultra3 uses the same 12-meter cable as Ultra2. The concern, therefore, is that - while bandwidth has been doubled with Ultra3 - the cable length has not changed. And, while Cardosi sees customers moving quickly to Ultra3, he questioned the lack of a revised cable specification for Ultra3. "We've increased the bandwidth with the new technology but haven't shortened the cable," he said. "Essentially, we took the same cable that was pushing 80 MBs per second, and we're now pushing 160 MBs through it. I was surprised that tighter cable specifications weren't developed."

Cardosi said he remembered the day when DPT extended the UltraWide cable from three meters to five meters. "We had data glitches. When someone is having data problems, the first thing we check is the cable. Is the cable connected properly? Is it a good cable? Is the cable length within the SCSI specification?"

Mylex's Mike Joyce was less concerned about the cable length for Ultra3. "I agree that the cable is probably the most important part of the system," he said. "And, while shorter cables are less apt to have data loss problems, there have been some improvements to the Ultra3 technology to address these concerns."

Cardosi and Joyce agree that these concerns aren't holding back the technology, though. "We're watching VARs move rapidly to Ultra3," said Joyce. "Ultra3 offers better performance at the same price as Ultra2. Everybody is looking for better performance, and Ultra3 will deliver that performance."

Mike Downing