I recently got a LaCie 2TB Thunderbolt bus-powered USB external rugged drive. I am using it with the Raspberry Pi 2 and it works fine. It's being used as a remote backup via rsync.
However, I am use to not leaving a rugged drive powered up all the time. I see no way to power down the LaCie drive when it's not needed for extended periods of time. My experience with self-powered LaCie rugged drives (larger in physical size) is that they run hot to the touch if left on all day even if there is no activity to the drive.
Does the Raspberry Pi 2 put external USB hard disks to sleep after a certain period of inactivity? If so, can this timer(?) be controlled? What is the default?