My computer setup consists of Lenovo x220 with a docking station, two external screens and of course mouse and keyboard. Even though my laptop has a fast hard drive, it has only 120GB disk space which means I need external hard drives to store my data. I have one external hard drive and one docking station which accepts regular internal 3.5" and 2.5" hard drives. Since I prefer suspend over shutdown I sometimes get problems with my external docking station.
Usually the error is something like this:
# umount /media/storage1
umount: /media/storage1: device is busy
Luckily there is a great tool called fuser which lets you identify the process using a file or socket. This means that I can easily find out which process is keeping my drive busy and simply kill the process.
To find out which process is keeping your drive busy
# fuser -mv /dev/sdXY
/dev/sdc1: 6772
In the command letter X is the drive letter and letter Y is the number of partition. The output gives the process id that prevents mounting/unmounting the drive by using the resources. Even though fuser can kill the processes using resources, it is generally safer to first find out what you going to kill.
ps auxw|grep 6772
haaja 6772 0.4 2.7 219212 56792 ? SLl Oct 3 02:25 banshee
Here we can see that I have banshee open and still accessing media files on my external hard drive. This was just a staged situation where I intentionally left banshee open and dried unmounting. Usually I have some terminal tab still open accessing the hard drive. I think that outputting the process information should be the default behavior of umount in this type of error situations. Kill the process and proceed to unmounting the no-longer-busy drive.