Hi all. Got an odd one here that I have only seen once before and I simply don't know enough about the inner workings of hard drives to diagnose.
I recently received a new WD external 1TB HDD. If I power the drive up, put it on the palm of my hand and rotate my wrist slightly the hard drive seems to noticeably "pull" itself in one direction or another. It's very strange - like inertia is forcing it to do this or that magnets are changing the centre of gravity completely. However I thought that the spindle and platters and calibrated in such a way that this would never happen. The best way to describe it is imagine the box was completely empty apart from a large marble made of lead - moving the drive in your hand forces the marble to move around the empty box, pulling it in that direction as the weight distribution has changed. That's pretty much the feeling you get with this external in your hand.
Surely it's a sign of a failed or dodgy drive. The last disk I had a couple of years ago that did this just completely stopped responding after a couple of months.
What technically could be wrong? Misaligned heads? Skewy spindle or platter mount? I realise the drive is spinning at 5400RPM but I've used drives from every manufacturer and this does issue does not plague 3 other WD drives I own. I basically need some ammunition because although I've been in IT quite a while I know the annoying sales assistant at the store in question will try and act as if this is normal.
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There's nothing wrong (yet), but moving a drive while powered will soon cause BIG problems.
It's called Gyroscopic Action (or Force) http://en.wikipedia.org/wiki/Gyroscope caused by the spinning platters.
I'm not convinced MrLinux. I have never had any other 3.5" drives in the past 10 years that have exhibited such strange behaviour. You're indeed correct that it is gyroscopic action, but the bigger question is why? Such inertia would not be caused if the platters were evenly weighted and the spindle aligned centrally.
It is indeed gyroscopic action, and what you're experiencing is exactly what you'd expect from perfectly balanced platters spinning at a high rate of speed.
A force applied at the 3 o'clock postition of a rotating mass will cause the axis of rotation to tilt as if the force had been applied at the 12 o'clock or 6 o'clock positions (depending on the direction of spin).
If you haven't experienced that with older drives then you haven't been paying attention. All drives I've ever used have had that characteristic. In some (lap top drives, for example) it's pretty subtle because the platters have less mass and they don't spin as fast. But it's there in all drives.
I too can verify that the other responses you've received are correct. I used to build computers for a living, and I have witnessed the action you're describing on all of the drives I've worked on. It is not an indicator of a bad drive. All spinning hard drives will do that.
I don't know the physics behind it, but I can definitely tell you that it's not cause for concern.