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New research promises denser disk drives

New research into "magnetic avalanches" offers insight into one cause of disk drive failure and could lead to breakthroughs in density, according to experts.

New physics research out of the University of California Santa Cruz (UC Santa Cruz) this month offers new insight into a poorly understood aspect of disk drive failures, according to industry experts, though they say the information won't necessarily make disk drives more reliable.

"There's been a misconception since this research was published that this is why disk drives fail, or that this is a new reason for drive failure unknown to the industry," said Josh Deutsch, who co-authored a paper that appeared online in the July 13 issue of Physical Review Letters. The research could theoretically help disk drive manufacturers find more reliable materials for disk drives, Deutsch said. He emphasized though, that disk drive manufacturers have been using materials with good damping capabilities for reliability all along -- it just wasn't until this research that the reasons were fully understood.

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He added, "this is far from the only reason drives fail -- it shouldn't be misconstrued as such."

The research came from a chance meeting at a lecture several years ago, between Deutsch, a theoretical condensed-matter physicist and a professor at UC Santa Cruz, and Andreas Berger, at the time an engineer for Hitachi Global Storage Technologies (HGST). It was that chance meeting that steered Deutsch's research in magnetics toward disk drives in particular.

According to a press release on the research, for each bit on a disk, the magnetic disk head grazes a tiny patch of the drive, forcing its polarity, or "spin," to align up or down, the magnetic equivalent of a one or a zero. The patch's polarity in many magnetic materials changes in a series of jumps that physicists liken to an avalanche.

Deutsch and Berger discovered that such an ideal model overlooked an effect, called spin precession that each magnetic field exerts on its neighbors, causing bits to swing in circles rather than flipping totally up or down, an effect that can cause a chain reaction of "wobbly bits" that wipes out a sector of a disk drive.

Better reliability vs. better density

However, while it's easy to equate this new insight with a breakthrough that will address recently uncovered discrepancies between manufacturer ratings and disk drive reliability, one of the authors of Carnegie Mellon University's drive reliability research, Garth Gibson, an associate professor at Carnegie Mellon, and chief technology officer (CTO) and founder of Panasas Inc., (Ed. note: When does he sleep?), said that since damping materials have always been used in disk drives, though until now their precise mechanism was not as well understood, the effect of these materials on drive reliability has already been taken into account in current statistics.

Meanwhile, "the single most important property of a magnetic disk drive is its cost," Gibson noted. While the new research into magnetic avalanches could be used to make drives more reliable through the use of better damping materials, Gibson predicted what will actually happen is that drive designers will use it to figure out how to get bits closer together with the same failure rate.

According to Gibson, disk drives are already a delicate balance between reliability, performance and affordability. A significant uptick in one of those categories has the potential to throw the others off balance. "There's an analogy here with the auto industry," Gibson said. "If we all drove around in tanks, fewer people would be hurt in car accidents, but that, of course, isn't practical." Better damping materials tend to be more expensive, and while it's possible some consumers are willing to pay more for more reliable disk drives, "historically, people want a low price more than anything else." Moreover, Gibson said, expensive improvements to just one relatively minor aspect of how disk drives operate probably won't be judged cost effective when there are so many other factors in disk drive failures.

Instead, he said, look for this research to come as a godsend to disk drive engineers tasked with reaching certain thresholds of density within set product roadmap time frames, who "often have no idea how they're going to get there more than a generation beforehand. Engineers are given an orderly process [for product development], but somewhere along the line, someone still has to make a [scientific] breakthrough."

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