How to have Debian Wheezy stop spinning/using a HDD?

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http://www.linuxquestions.org – There is a harddrive in my box that appears to be spinning. I don't know why it is spinning, because it is not mounted. However, it is clicking. I would unplug it, but I don't want to. Is there a command-line way to have the computer stop accessing it? (HowTos)