Correct way to disconnect/eject an USB hard disk ?

[Manish Jain]

On 2020-08-19 22:06, Manish Jain wrote:
> 
> 
> On 2020-08-19 21:12, Gary Aitken wrote:
>> Can you explain why I have seen umount commands return, and then the
>> USB device "activity" light keeps blinking?  I have on occasion waited
>> for a while and it keeps blinking, and eventually I just unplugged it.
> 
> No idea, Gary.
> 
> But umount only returns when pending I/O has been flushed to the device. 
> If the device's activity LED still keeps blinking, there are two 
> explanations I can think of :
> 
> 1) The LED sensor is either faulty or is simply signalling availability 
> of power (in case there is no separate power LED).
> 
> 2) The device has some internal flash storage intermediate to its main 
> storage area. While umount could return when data has been sent into the 
> flash buffer, the device still has to internally reallocate the data to 
> main storage (as might be the case with SSHD: solid state hybrid disk). 
> In such case, it would be prudent to wait for the LED to stop blinking 
> before unplugging the device. But if the LED keeps blinking forever, I 
> would think there is some fault with the LED itself.
> 
> Poly, your comments ?
> 
> 
> Regards,
> Manish Jain


I have an idea which you could use to test the LED's goodness. Connect 
the device, mount, and copy in a few large files (3 or more ~1 GB video 
files should be okay) into the device (with `cp -v`). Note the name of 
the last file to get copied.

Immediately after cp returns, umount. Immediately after umount returns, 
unplug.

Replug the device and remount. If cmp indicates the last copied large 
file is the same as the original, your LED is faulty.


Regards,
Manish Jain