Pine Man 10:18 23 Jun 2017
The icon for the external hard drive will be shown in the sidebar usually with the name of the manufacturer. Underneath that icon their maybe others to indicate partitions or items such as Time Machine on that external drive.
To erase/repair the entire external drive select the topmost icon (manufacturers name) then select the action you want to carry out using the options at the top of the window. Erase etc etc.
