The label on one of my new hard drives says the following:
Caution. Product warranty is void if any seal or label is removed, or if the drive experiences shock in excess of 350 Gs.This piqued my curiosity, so I checked the specifications (extra click needed because of Javascript) and it turns out that the drive supports "nonoperative shocks" up to 300 Gs.
Does anybody know how that translates into real-world measures? In my experience, hard drives are pretty fragile even when they're powered down...
7 comments:
I don't know exact numbers by which to really judge this by but my dad, who knows about these things, tells me that the force these drives can survive may sound high but if you drop a hard drive specifically by its corner, onto a hard surface, then that's a lot of Gs, a lot more than you'd expect.
Pete Boyd
Basically, it's a lot of force for a very short period of time. But still enough to cause the heads nail the platters. The smarter drives have intelligence to move the heads somewhere kinda safe if an accelerometer detects a fall or impact. It might not be too late by impact to move the heads if the movement is fast enough, but I suspect they're often not.
Sadly I don't have hard numbers but if I recall correctly, SD cards have a rating around there, just because they're not very rigid. It seems like solid state stuff with no moving parts still has a better chance to me, but maybe we just buy the cheap stuff.
A "G" is a colloquial unit of acceleration. Named after Gravity, which accelerates at about 9.8 m/s/s (metres per second per second, usually expressed as m/s^2 but I can't use superscript here). So 300 G is roughly 3000 m/s/s.
Say you drop a hard disk from a low desk 1 metre from the floor. When the disk reaches the floor it will be travelling at 9.8 m/s (I'll round that up to 10). The thing about the shock is that once it makes contact with the floor, it will decelerate very quickly. I'll take a couple of scenarios with figures taken from the top of my head. I'm also assuming that the disk falls on one of its faces, so it receives the full shock (deceleration) on immediate impact.
Consider it falls on carpet. The carpet will give the disk 5 mm (0.005 metres) in which to stop moving. Assuming a constant deceleration:
10 / 0.005 = 2000.
2000 m/s/s is two thirds of its rated shock, so in this case your disk is still OK.
Now consider it falls on concrete. I'm going to assume that the concrete will flex by one-fifth of a millimetre, 0.0002 metres. (I think that is probably an over-estimation of how much the concrete will flex, really.)
10 / 0.0002 = 50 000
The disk will hit the concrete at over 16 times the rated shock warranty.
So the the moral of the story here is that if in normal language, you consider the disk to have experienced physical "shock", it is probably over the 300 or 350 Gs mentioned on the label.
One addendum to tedp's decription. Generally, you're said to be experiencing one G while sitting inertly in your chair. And during a free fall, that's zero Gs, even though this would be where you're actually accellerating at.
So generally speaking, I guess it'd be wiser to say that Gs is a measure of normal forces, but nobody remebers / knows what that is anyways.
Thanks, everyone! Handling hard drives with care is still necessary, I guess. :)
Sorry guys, but you're all wrong. Gs has nothing to do with gravity (which is a lower case g anyway) or s meaning seconds (or time), Gs stands for Gauss, a measurement of magnetic flux. HDD's are affected by magnetic shock (flux) and this is what it refers to.
Ignore the comment "HDD's are affected by magnetic shock (flux) and this is what it refers to" . This post is out in bleachers with the physics-flunking cheerleaders. The others posts are correct.
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