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Yes, I know somewhat about the possibility of data corruption if there was data that hadn't been all written to it.

But I just saw this:

Note:If u remove HDD(not USB sticks) without safely removing it,its not healthy and will affect life.

So, if nothing is actually writing to it, could there actually be any harm caused by not safely removing or unmounting it before disconnecting it?

By the way, if I'm way off about any of this, please correct me.

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good question...+1 –  studiohack Apr 2 '10 at 2:31
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2 Answers

up vote 5 down vote accepted

No! Cached data may not be written yet. Regardless of your OS, you have to inform it that you're yanking.

OSes do write-caching (and read-caching) to make drive access faster.

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What if I never actually wrote any files to the disk, I only read files? –  heavyd Apr 2 '10 at 1:45
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Some file systems include last accessed times in the file metadata so reading a file DOES write to the disk. –  Chris Nava Apr 2 '10 at 2:36
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@Nathaniel no. But in many cases you can take your chances and nothing bad will happen ;) –  Yar Oct 8 '10 at 22:44
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@Thorbjørn Ravn Andersen makes sense and matches my empirical observations (i.e., I just unplug drives randomly all the time, with no ill consequences :) ) –  Yar Oct 23 '10 at 22:29
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@Nathaniel, I might mention that one app that accesses stuff when you least expect it is the Finder itself. So learning to kill tasks on the OS is essential, but you probably know how to do that already. –  Yar Oct 23 '10 at 22:30
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When you run the safe removal process, commands are sent to the disk to cause it to spin down and park the heads: in contrast if you disconnect the power suddenly then an emergency unload is done, which uses remaining power to move the heads away from the surface. That movement is violent and so disks are rated for a far fewer number of emergency unloads than the standard parking of the heads. So by pulling the power you may indeed be causing physical damage to the actuator mechanism.

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That... is a good observation. –  Nathaniel Nov 23 '10 at 0:52
    
I have an external hard disk which is never can be safely removed (it always says "Cannot remove, still in usage" or something like that). Would you be so kind to give a tip to make it safely removable? –  deathlock Jun 25 '13 at 14:36
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