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I am running Ubuntu 12.04. When I unmount (eject) USB disk, the power LED is always "ON" & I can feel disk is still spinning after 10 Minutes.

This means disk is not unmounted from system? is it safe to disconnect the USB cable? I does not want to damage my external disk.

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What are the specs of you external? –  Mitch Aug 23 '12 at 10:37
    
My answer here might be useful askubuntu.com/questions/56270/… –  user76204 Sep 19 '12 at 19:47

2 Answers 2

Yes, after you eject a drive it is safe to disconnect the USB cable and/or cut the power (if the drive uses a power adapter). If you unmount it, just make sure that if it has multiple partitions, all if them are unmounted.

Ejecting or unmounting an external hard drive does not always make it spin down or power down; that behavior is up to the controller inside the hard disk which interfaces between USB and SATA. Ejecting simply tells the drive to finish any pending read/write operations and then ceases all communication.

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I can verify that this is normal behavior on all of my USB external hard drives. The hard drive controller will not spin down as long as it has power. Just make sure all partitions are unmounted and unplug it and you will be fine! –  adempewolff Aug 23 '12 at 11:45

Try running the udisks --detach /dev/sd[letter-of-the-disk] after unmounting the partitions and see if the disk spins down after that?

From the man udisks:

--detach device_file [--detach-options options]

Detaches (e.g. powering down the physical port the device is connected to) the device represented by device_file using a comma-separated list of options.

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