Addressing rotational vibration to optimize where data lives

An economy car and a luxury sedan may share many of the same primary components, such as hybrid powertrain and chassis structure. But tack on a host of value-add amenities, from leather interior to proximity cameras to app-toting in-dash computers, and the same underlying economy car can become a luxury vehicle suited to a different set of user priorities and expectations.

Reliability is the driving force behind all hard drive market segmentation.

Similarly, when a new drive design finally rolls off the product development process (PDP) pipeline, it's not quite ready for a model and serial number sticker. Seagate engineers now have a wealth of data revealing how that design behaves in a variety of situations. It might, for example, demonstrate a markedly higher tolerance to rotational vibration and longer mean-time between failure (MTBF) at higher temperatures when the spindle is loaded with four or fewer platters rather than five or six. In such a case, a four-platter version of the design might become a 4 TB drive targeted at small business NAS solutions while the 6 TB six-platter incarnation would still meet all expectations for a consumer desktop drive. Perhaps if the motor is anchored to the top cover as well as the bottom, and rotational vibration (RV) sensors are applied to the circuit board to help cope with conditions in larger NAS and server/storage environments, then the same drive design might even qualify for top capacity nearline applications. In this way, one drive design can ultimately serve a variety of markets under different model families.

This isn't to say that one drive design covers all storage categories any more than one car design serves all vehicle markets. Seagate uses multiple platforms as starting points, and the more a platform is made to fit this or that market segment, the more it will skew toward those respective categories.

Motors and moving parts emit vibrations, and so hard drives, with their platters spinning at several thousand RPM and the rapid motions of their voice coil motor, emit RV forces. Like someone bumping a spinning record player and causing its needle to skip across the groove, vibration can cause a hard drive's read/write head to misalign with the underlying track, resulting in errors or slower performance if a re-read has to be performed. One drive alone puts out little vibration, which is why drives intended for desktop PCs don't need much RV tolerance. However, pack many drives into a small chassis, especially one without vibration dampening features, and those drive vibrations can coalesce and result in spikes that, in extreme cases and over time, can literally rattle a drive to death. Drive-dense environments are particularly common in data centers. Tack on vibration from chassis cooling fans and the heat generated from all of the electronics in the enclosure, and the conditions in something like a high-end NAS box or storage server can add up to a perfect storm for drives.

Different drive types are designed to withstand varying levels of ambient RV. A desktop drive's performance begins to decline soon after being exposed to more than light fan vibration, and its performance will plummet nearly to zero in hostile, enterprise-grade environments. Conversely, business-class drives built and qualified through PDP for such applications and situations continue to perform at very high levels. The question is not whether a drive can operate in a given place but whether it should.

In a way, reliability is the driving force behind all hard drive market segmentation. Market research and demand informs Seagate that consumers want hard drives able to perform eight hours per workday with a workload rate limit (WRL) of 55 TB/year while businesses running surveillance applications need 24/7 storage writing 180 TB/year. The applications and environments demand reliability at those respective levels.