Accessing External storage through web.config

I have a folder on website named ~\ProductImages containing many images, I installed an external HDD via USB to server with drive letter F:\ but cannot access the images via web.config <add Key=""> to new directory on HDD. I shared the directory with read permissions to Everyone, but no success. Any suggestions welcomed..

//current configuration that works
<add key="ProductImages" value="~\ProductImages\"/>

//new configuration that does not work
<add key="ProductImages" value="F:\\ProductImages\" />

Thank you
Edski...