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The advancements in disk drive technology have been as influential to the progress of business computing as microprocessors. Without the capacity and performance advances we've come to take for granted, it would be impossible to run the majority of today's applications and operating systems.

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Enter SAS
There's another new serial disk drive interface being developed called serial-attached SCSI (SAS). The original idea behind SAS was to create another small I/O network that supported SCSI commands, as opposed to ATA. The initial problem with SAS was that Fibre Channel already provided SCSI compatibility for both external and internal interfaces and there was really no need for another disk drive interface.

However, the SAS backers saw the advantages of piggybacking on the work already done on serial ATA (SATA) and worked with the SATA organization to create a specification that incorporates SATA connectivity to SAS controllers. The idea is that a single controller could connect to SATA and as SAS disk drives. From my perspective, I'm not sure how commonly this will be done. SATA drives will provide most of the performance and reliability needed and applications justifying high-performance storage can probably also justify dedicated storage subsystems tuned to the application.

At this point, it's hard to say if SAS and SATA controllers will coexist in the market, or if one will eat the other's opportunity. The primary advantage of SAS will be the ability to connect low-cost SATA disk drives. If SAS has problems with SATA connectivity, it probably won't survive.

It's almost ridiculous to propose how large-scale storage could be accomplished without disk drives providing the fundamental storage function. There are other potential technologies that could be used in place of disk drives, such as nonvolatile memory and optical recording devices, but disk drives have the best combination of reliability, performance, cost and operating requirements.

The last company that attempted to create a new storage technology was TeraStor, based in Milipitas, CA. It failed to deliver competitive technology after burning through $80 million of venture funding several years ago.

There's nearly universal interoperability among disk drives, which means customers can choose products largely based on price. The competitive pressures and the imperative to develop new, inexpensive drive technologies were chronicled in Clayton Christensen's groundbreaking book, The Innovator's Dilemma, which theorizes how new, disruptive technologies create lower-cost price trajectories for replacement products. In his book, Christensen uses the disk drive industry to show how the rapid churn rate of disruptive technologies put the disk drive industry in the low-margin dungeon where it is today.

Continued improvements in existing disk drive technologies that boost performance and reliability are permitting organizations to start migrating their storage plants from expensive server-class drives to less expensive desktop drives without much risk. Along with the changes in drive technologies, there are two key enterprise storage technologies facilitating this migration: RAID and storage area networks (SANs). A third technology, serial ATA (SATA) is a new disk drive interface that, with RAID and SANs, will allow IT organizations to achieve more of their strategic storage goals at far less of a cost.

Drive classes
Historically, disk drives gravitated into three distinct product classes: desktop, server and laptop. Desktop drives were designed for mass-production with slower performance and moderate duty usage. Server drives were built for the rigors of transaction processing and round-the-clock duty cycles. Finally, laptop drives were made to fit the physical demands of portable computers. From a business perspective, desktop drives have the highest sales volumes and lowest margins, while server drives represent the lowest sales volumes and the highest margins. Server drives typically sell for three to four times as much as similar capacity desktop drives.

While the three product classes were distinct, technologies invented for one class of drive are often integrated into the other classes. For instance, a volume manufacturing process developed for desktop drives can be applied to the production processes of server drives to reduce costs. Conversely, a performance technology developed for server drives can be adopted by desktop product families. Over time, the lower-performing desktop drives inherit the high-performance capabilities of server drives, as the server drives rise to new performance levels.

Competitive pressures between drive manufacturers for the high-volume desktop market nearly guarantee that new performance technologies developed for server drives make their way into desktop drives within two to three years. This year, we're seeing desktop drives reach the 10,000 rpm plateau--a performance specification that had previously only been available for server-class drives.

Generally, desktop drives sold today compare favorably with the performance of server drives that were sold three years ago. By comparison, the performance demands of many applications haven't increased as much. For example, the I/O performance requirements for Windows Exchange servers haven't increased much, if at all, in the same time frame. To use Clayton Christensen's terminology, server-class drives overshoot the requirements for most applications. The performance of today's desktop drives is more than adequate for most server applications.

This was first published in October 2003

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