Unmounting hdd

[laragheast]

Hi
I have a 2014 iMac 5k with fusion drive
And have added LaCie hdd external
It's noisey enough so when it's not in use
I unmount it but sometimes it won't unmount because finder is using it I only have some films on it so I don't know why finder is useing it , any ideas would be great thanks .

 

[Taz Mangus]

When this happens next time, open the Activity monitor application in the Utilities folder. Click on the Disk tab and double click on a process and a process window will popup. Click on the "Open Files and Ports" tab. This will show all the files that are currently being accessed by the process.