Large external storage stops working after being connected for a long time I have a 4 TB LaCie RUGGED USB-C external hard drive, and when it's connected to my MacBook Pro (13-inch mid 2014) for a long time without being used, it stops working. I do allow drives to sleep when connected in the settings.


Icon remain on desktop, but trying to open it or ejecting it, causes Finder to hang. 
When I unplug it, Finder unblocks
When I plug it in again, it’s working (for a while of course)
The drive is bus powered and does not have an external power source


I use this drive for Time Machine backups, but sometimes Time Machine fails to backup. 

I’d like to isolate the issue to know if the Mac is the problem, the cable is the problem or the drive is the problem or I need to change settings.

Can I use a system log or Time Machine log to diagnose what’s happening?
I searched around and found out that there's an option in Energy Saver: Put hard disks to sleep when possible and it's checked on my Mac. You can see the option in the screen shot below: