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The Factors Behind NLL...Continued

Moving Into the Lite
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Hard drives can attempt to cope with vibration in several ways.

Let’s take a closer look at the above graphic supplied by Seagate. A standard desktop (DT) drive without a microactuator or RV compensation will begin to experience write impairment practically at the first sign of vibration, and the amount of impairment escalates rapidly as vibration increases. Assuming an environment in which 10 rad/sec2 conditions are present, this desktop drive will write data at less than 20% of its normal performance. A better-quality desktop with vibration-dampening microactuators, such as the Seagate Desktop HDD (formerly Barracuda® drive), will achieve roughly 70% of regular write performance under these conditions. Obviously, microactuators make a significant difference, but the point remains: Even high-quality desktop drives take a tremendous hit in the presence of ambient vibration.

RV compensation offers much more benefit than microactuators. While microactuators are designed to suppress emitted vibration, RV compensation copes with vibration as it affects the drive. We see the difference in the yellow line, which can maintain 90% or so write performance without microactuator assistance at 10 rad/sec2. But even this pales beside a true nearline drive. The Constellation® CS drive experiences no impairment whatsoever before 15 rad/sec2 is reached, and the Constellation ES.2 drive hums along until 25 rad/sec2. Also note that both nearline models have much less performance fall-off as vibration increases compared to desktop models.


In general, desktop drives have an RV tolerance of up to 300Hz. In a single-drive, desktop-type environment, this tolerance is more than sufficient to cope with most ambient vibration conditions. As the number of vibration sources increases, though, desktop drives will prove more error-prone. In comparison, nearline drives often demonstrate RV tolerance of up to 1500Hz.

Again, in desktop settings, the RV discussion is fairly moot. But when storage enclosures and servers are in play, especially in rackmount environments, RV tolerance should always be taken into account.