What causes hard disk failures in general. I would like to know the common causes and how to prevent such incidence.
A hard drive is basically an electromagnet record player sealed in a case. All it's control systems are attached to a circuit board outside the case, and the platters, spindles, and drive heads are inside the case. So there are really two major buckets for hard drive damage: electronics issues and physical issues.
The circuit board on the outside of the drive can fail for many reasons.
- Temperature Extremes
- Electrostatic Discharge
- Anything else that causes a circuit bored to fail
A dead board will pretty much kill the affected drive, but the data should be unaffected. Control boards can be replaced but are custom to the exact drive you are using so you'll need the exact board AND firmware. Otherwise you'd need to work with a professional recovery services.
A hard drives platters spin at very high speed with the drive heads being in very close proximity. One of my profs explained it thusly, "Imagine a 747 flying maximum speed about nickel's diameter above ground, and you've got the right idea."
There are several classes of potential damage here:
- Motor failure
- Over time small drops, walking around with a running laptop, power outage while the drives are spinning as the actuator arms with heads are engaged will cause the heads to hit the platter and causes cuts or scrapes.
- Catastrophic case damage (eg. I dropped my laptop off a 5th floor window)
- Excessive bad sectors will cause the drive to say that its failing
The best explanations of how Hard drives works and how to fix damaged drives are Scott Moulton (speaker at defcon, toorcon, etc.) at http://www.myharddrivedied.com/presentations/
The majority of disk failure is due to either damage to the magnetic layer, wear or damage to the spindle bearings or failure of the electronics.
Damage to the magnetic layer is most often caused by the head touching the surface of the platter, either through mechanical jarring of the drive or contaminates getting between the two.
Damage to the spindle bearings is generally through simpe wear and tear, which normally takes quite a few years, of mechanical jarring.
Damage to the electronics can be caused by power spikes of poorly regulated supplies but is most commonly simple device failure.
Good answers above. Google also did a paper discussing disk failures.