Conventional hard disk drives (HDDs) are designed to reliably operate in the hospitable physical surroundings of interior deployments, which are typically characterized by mild temperatures, stable humidity and modest levels of vibration. By contrast, outdoor and mobile storage environments can entail anything from sweltering heat or sub-zero frost to oppressive dampness and pounding vibration. And all may be encountered miles above sea level. So it’s no surprise that bringing the benefits of HDD-based storage to outdoor and mobile settings such as automotive, industrial PC, field computing, and military applications poses a formidable challenge to engineers.
How is it possible to maintain the consistent performance and reliability of hard disk drives when they are exposed to such a broad range of harsh external conditions? The solution may be a new breed of purpose-built HDDs, specifically designed to withstand the temperature, vibration, shock, altitude and humidity extremes that are endemic to many outdoor and mobile storage situations. Ruggedized disk drives, like the Seagate EE25 Series™ for example, are being specially designed to ensure reliable performance in punishing physical surroundings. To appreciate the magnitude of this challenge, remember that HDD storage relies on magnetism to store and retrieve data on a drive’s platter(s).
This arrangement is made possible by the extraordinary proximity of the read/write head to the platter surface. Riding a few nanometers above the rapidly- spinning platter, the complex read/write head system has been likened to a Boeing 747 flying at 600 miles per hour — six inches off the ground. A variety of adverse environmental conditions can disrupt this arrangement and prevent a hard disk drive from delivering optimal throughput, reliability and data integrity. The following are brief discussions of the most significant environmental issues facing an outdoor or mobile storage HDD, and how new generations of ruggedized disk drives are employing remarkably innovative designs and technologies to overcome them.
One technology being used in new ruggedized drives is perpendicular magnetic recording (PMR), which delivers greater capacity per platter and also enables higher write fields to be achieved. This, in turn, results in media with improved thermal stability (less thermal decay). In effect, PMR gives more design margin to maintain consistent performance and reliability across a drive’s full range of operating temperatures. In addition, HDD manufacturers can utilize improved electro-mechanical materials to achieve more stable read/write performance at extreme temperatures, which is further aided by enhanced firmware technology. Complementing this firmware, more sophisticated temperature-sensing hardware allows the drive to sense and adjust to temperature fluctuations more accurately. This temperature output of the drive can also be delivered to the host on command. Another material that enhances the HDD’s durability under extreme temperature conditions is a new low-viscosity lubricant that is used for the fluid dynamic bearing (FDB) motor. The lubricant ensures the appropriate motor spin speed can be achieved at extremely cold temperatures while still maintaining stability (resistance to evaporation) at high temperatures. Developed to work with extremely close-tolerance bearings, this lubricant also maintains superior film strength at high temperatures.
Outdoor and mobile HDDs are designed to operate in the wild and thus must offer far more robust vibration tolerance than conventional drives. Advanced hardware/firmware technology enables ruggedized drives to sense both the quantity (amplitude) and character (synchronous vs. asynchronous and lateral or vertical direction) of incoming vibration and intelligently adjust the drive’s response based on info from the drive’s sensing mechanism.
Shock can be broken down into two basic categories, based on duration: shorter- duration inputs (hard and sharp impacts similar to dropping a disk drive directly on a solid table) and longer duration inputs (softer and slower impacts such as that encountered by a drive mounted in an automobile that hits a pothole). By employing more robust materials in HDD construction and using sophisticated shock sensors that can intelligently monitor and temporarily pause writing when large shocks are encountered, contemporary ruggedized drives are able to improve capability with longer duration shocks while still maintaining robustness in shorter duration shocks. Because the shock adjustments are managed so swiftly, they are transparent to the user, and a larger cache enables seamless video streaming even in in exceptionally bumpy environments.
Variations in air density caused by changes in altitude (or temperature) can affect the flying height of a drive’s read/write head. Note that the strength of an object’s magnetic field rapidly falls off as distance from it increases; this principle applies to both the magnetism of the read/write head and the magnetic bits on the disk surface. Thus, to efficiently and reliably write and read information, the head must remain a very close and consistent distance from the platter. Design advancements that offer greater immunity to variations in ambient air pressure can deliver more stable performance in extreme altitude environments. Seagate, for example, has gone so far as to evaluate high-altitude/ low-pressure performance at the summit of Mt. Everest.
Excessive moisture arising from elevated humidity levels can adversely affect the electro-mechanical components within a disk drive. HDD manufacturers are going to great lengths to ensure that moisture and other contaminants won’t degrade performance or reliability.
Hard disk drives are remarkably complex systems, and innovative technologies, materials and construction methods promise to profoundly advance ruggedized HDD storage. Utilizing new testing regimes to simulate punishing conditions (far more rigorous than standard HDD tests), companies will be able to harness the reliability and durability of drives designed specifically for extreme environments.
This article was written by Preston Sellers, Senior Engineering Manager, Seagate Technology (Scotts Valley, CA). For more information, contact