Researching the history of Disk Storage and RAID since Patterson et al's 1988 paper has given me some surprises. Strictly personal viewpoint, YMMV. Aerodynamic drag of (disk) platters is ∝ ω³ r⁵ (RPM^3 * radius^5) If you double the RPM of a drive, spindle drive power consumption is cubed. All that power is put into moving the air, which in a closed system, heats it. Ergo, 15K drives run hot! If you halve the size of a platter, spindle drive power consumption is reduced by the fifth-power. This is why 2½ inch drives use under 5W (and can be powered by USB bus). There's a 2003 paper by Gurumurthi on using this effect to dynamically vary drive RPM and save power. Same author in 2008 suggests disks benefit from 2 or 4 sets of heads/actuators. Either to increase streaming rate or seek time, or reduce RPM and maintain seek times. The Dynamic RPM paper to be the genesis of the current lines of "Green" drives. Western Digital quote RPM as "intellidrive", but class ...
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