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This is a general question that came out of a specific comparison between the Western Digital Scorpio WD3200BEKT and Western Digital Scorpio WD3200BJKT (which is the same as the former but with a free fall sensor.) Note: I'm not asking for a review or appraisal of these specific drives, as the general question does apply on other brands as well. Though your input would help my decision.

To break down the general question in order to answer it, I would be looking for comments on things like:

  • if it's necessary to have differing physical dimensions between free fall sensor drives and those without, e.g. does it make it any thicker, and therefore reduce the systems where it can be installed - particularly smaller laptops?

  • does it actually make the system less reliable - because of false alarms whereby the drive thought the laptop was falling but it wasn't?

I suppose that the fact that a manufacturer produces both drives with and without free fall sensors says something about possible disadvantages. Or it could be standard marketing techniques where by making drives with and without results in larger sales volume than just those with the feature alone.

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No difference in size, the only thing that changes thickness is how many platters are in the drive, standard drives are 9.5mm then they have some 12mm drives these days. I know of no disadvantages. –  Moab Sep 16 '12 at 4:50
    
+1 Thanks Moab for your input. –  therobyouknow Sep 16 '12 at 11:37

2 Answers 2

up vote 4 down vote accepted

Are there any disadvantages of having a “free fall sensor” on a hard disk drive?

Nope.

if it's necessary to have differing physical dimensions between free fall sensor drives and those without, e.g. does it make it any thicker, and therefore reduce the systems where it can be installed - particularly smaller laptops?

No. As you can see, even a typical 2.5" laptop drive has enough space for the tiny component.

enter image description here

does it actually make the system less reliable - because of false alarms whereby the drive thought the laptop was falling but it wasn't?

Not generally, no. The sensor is specifically calibrated to detect free fall (like the laptop being dropped), not just minor bumps.

If a laptop is dropped, it will experience a a moment of weightlessness and then a sudden and relatively massive increase in shock (g-forces). For hard-drives in which a head is floating on a microscopic cushion of air above a disk spinning at thousands of revolutions per minute (Scott Mueller analogized it as a jumbo-jet flying a few feet off the ground), this can be/is usually quite harmful and results in a catastrophic head crash.

Hard-drives (usually laptop drives) with free-fall sensors are designed such that when it detects that the drive is falling (usually the whole system), then it tries to park the head(s) quickly so that when it hits, the heads are on a non-data section of the platters. This by no means guarantees that the drive will survive; it can still kill it if the shock is severe enough, but at least the platters will still have their data intact (unless the shock is somehow astronomical enough to actually jolt the magnetic bits around).

If the laptop is merely bumped, then the sensor should not trigger since it is calibrated not to. Instead, what may happen if the bump was hard enough and the drive happened to be active at the moment is that it will encounter a read or write error and log it in the SMART table: G-sense Error Rate: The count of errors resulting from externally induced shock & vibration.

Usually however, it will just try the read/write again and unless you see other, more critical SMART values rise, then nothing particularly bad happened.

I suppose that the fact that a manufacturer produces both drives with and without free fall sensors says something about possible disadvantages.

Or it is just a way to sell a more expensive model.

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+1 Great answer @Synetech and accepted. –  therobyouknow Sep 18 '12 at 11:26

Free fall Sensor is a part of Active Hard Drive protection and is only suppose to react in a free fall state. That being said, it would not make it less relaiable as it will try to park the head to avoid physical damage to the platter. But it may be a bit less productive if you are typing out a novel on an international flight that has alot of turbulance, but your data, scripts and story line should be safe.

Moab answered the size question in his comments.

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+1 Thanks for your input @Carl B –  therobyouknow Sep 18 '12 at 11:26

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