ATA puts the squeeze on SCSI

Consortium to develop Serial SCSI spec


Analysts say it is no longer a question of if, but when and just how much market share Serial ATA will take from SCSI over the next four years. International Data Corp., for example, expects Serial ATA to not only hit SCSI hard on the desktop, but also to threaten traditional SCSI hard-drive strongholds in the enterprise.

According to the Framingham, MA, market research firm, nearly 50% of all hard drives shipped into the enterprise segment will have a Serial ATA interface in 2005, while SCSI will lose nearly two-thirds of its current market share over the period (see figure on p. 16).

Fibre Channel, meanwhile, will continue to hold its own as a high-end interface with advanced features and functionality that justify its higher cost, reports IDC. As such, Fibre Channel drives are expected to steadily increase market share over the four-year period, to about 25% of all enterprise drive shipments in 2005.

But this forecast pre-dated a November announcement by Compaq, IBM, LSI Logic, Maxtor, and Seagate to jointly develop a serial-attached SCSI (Serial SCSI) specification (see sidebar). The initial product road map, which will be loosely tied to that of Serial ATA, calls for 150MBps and 300MBps Serial SCSI drives in the 2004 time frame (see table).

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Does this news change the overall market picture? "Yes," says Dave Reinsel, IDC's hard-disk-drive analyst and author of the IDC report, The interface race with desktop hard disk drives. But just how much of an effect Serial SCSI will have on Serial ATA adoption will largely depend on how quickly Serial SCSI drives hit the market, he says.

"The question is: 'Will Serial SCSI be enough-and in time-to prevent Serial ATA from making great strides?' " asks Reinsel.

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In addition to improved performance, Serial ATA offers simplified cabling, a lower pin count, and lower power requirements than parallel ATA, and it is a point-to-point configuration.

Reinsel says that if his current forecast proves true, and Serial SCSI does not become a viable drive interface before 2004, the hard-drive industry could see as much as a 4% decrease in gross margins by 2005. With margins hovering around the 15% mark today, such a decrease, he warns, may not only destroy any possibility of a return to profitability for the industry, but may spell further consolidation.

Similarly, Reinsel says a switch to Serial ATA from Ultra ATA/133 on the desktop will initially add cost to the overall PC system and lower already-low desktop margins. Last year, the enterprise drive market saw 30% margins, while the desktop margins averaged 10%, he says.

"The possibility of a 4% decrease frightens me," says Reinsel. "The bottom line is that Serial SCSI drives need to be out in 2003." Initial Serial ATA drives are expected in the second half of this year.

ATA's appeal

So, what is it about ATA that has users-and vendors-so excited? It boils down to two things: cost and performance. Simply put, ATA drives are getting faster and cheaper. Today, ATA tops out at 133MBps (Ultra ATA/133), but 150MBps (Serial ATA) is right around the corner, and the Serial ATA road map calls for at least two more generations with speeds to 600MBps.

As for cost, IDC estimates that the aggregate average selling price of desktop ATA drives will drop to $0.003 per megabyte, which means that the cost of configuring an ATA RAID array is rapidly approaching that of a tape library, says IDC's Reinsel. Similarly, ATA drives are becoming more common in low-end network-attached storage (NAS) devices.

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"It used to be simple," writes Stephen Fuld in the recent Evaluator Group report, entitled Are IDE/ATA disk drives a good match for enterprise systems? "You chose IDE/ATA drives for desktop systems, and SCSI or perhaps Fibre Channel drives for servers...[Today,] the answer..., 'It depends.' "

Fuld points to the dramatic price difference between the two drive classes, improvements to ATA's performance and reliability, and the advent of RAID controllers and cache controllers as key reasons for ATA's traction in non-desktop markets. To determine which drives are right for your situation, Fuld says users should, among other things, consider the following:

  • Price-Approximately 80% of the cost of a storage system can be attributed to the disk drives themselves. The price differential between the two drive classes (SCSI and ATA) is approximately 2:5 to 1.
  • Performance-Using multiple ATA drives, versus one enterprise-class drive, could increase your throughput while saving you money (see figure). Other performance metrics include drive rotational speed, latency, seek time, media rate, and buffer size.
  • Robustness-The unrecoverable error rate is one to two orders of magnitude better for enterprise- versus desktop-class drives.

This article was originally published on January 01, 2002