I had the 1.5 TB drive and it used to do it, then it stopped, then it had HDD issues and I got this one.
I am not sure if it is everytime but when it resumes the Ext HD is not there and I have to reboot to get it back. It should just be there.
Win 7 Pro x64
Gigabyte GA-790XTA-UD4P Socket AM3 790X Mobo
AMD Phenom II x4
Hooked up via eSata. USB is not an option as it is slower and I bought this because of eSata.