How long does a hard disk spin after power off

hard drivehardware-failurespinup

I frequently use 3.5" hard drives in external "docks", swapping them in and out. The platters are heavy and have great angular momentum and I imagine that if the drive is moved – especially rotated out of the plane – while the hard disks are spinning that would be bad for the bearings, and reduce the life of the disk. So how long does it take for the disk to spin down so that it is safe to move? (I'm not so worried about the head mechanism and head crashes as I'm sure it retracts to a safe position extremely rapidly on power off.)

So my set of closely related questions (totally suitable for a single answer, though answering any one of the questions is of course acceptable and desirable) is:

  1. Is my imagination above, that twisting the disk drive out of plane while the platters are spinning can damage (or reduce the life of) the drive, correct?

  2. How long do I need to wait, after power off, before twisting the drive out of plane?

  3. How long should I wait, after power off, before moving the disk much at all?

  4. So anyway, how long does it take for those platters, rotating freely on bearings designed to be as friction-free as they can be made, possibly even in a helium medium, to spin down from 7200RPM to full stop? Or are there brakes (magnetic or otherwise) that slow them down?

  5. I have occasionally, unmindfully, moved a hard disk out of plane without waiting any length of time. I could swear I've felt a pretty strong gyroscopic resistance. Final question: Was that real or just my overexcited imagination?

(I added the "spinup" tag just for fun. There's no "spindown" tag – if there was it would probably have had a Q with the A to this question!)

Best Answer

  1. As you state, gyroscopic forces on a spinning disk cause precession if the disk is tilted, so tilting a spinning platter would put some additional strain on the bearings. That said, it depends on how rapidly the disk is spinning and on how abruptly it's tilted. Gentle handling of even an operating is acceptable. Consider computers with HDD's operating aboard rolling, yawing ships... yet their lifetimes must be considered acceptable. (Of course, damage from salt spray has to be mitigated.)
  2. Since disk drive spindles are driven by permanent magnet motors, whether considered brushless or stepper, there is a cogging, braking effect, easily seen when operated at low speeds, as in this video starting at 6:10. The permanent magnets also induce eddy currents in the rotor, which causes the rotor to spin down in just a few seconds. On most modern HDD's, the platter is stopped within ten seconds or so of shutdown. Of course, older disk drives took considerably longer to spin down (or up). (See an early design model at 6:00.)

So, all things considered, within ten seconds of powering down, I'd be comfortable moving a 3.5" HDD.

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