Exclude external hard drive

Hello forum,

Recently I am struggling with ejecting an external hard drive safely. I suspect Sophos of using it. So, could someone tell me how I could exclude the external hard drive from being scanned by Sophos Protection if it's even possible?

I tried to configure it via Configure -> Anti-virus -> On-access scanning and then the Exclusions tab but that's all abracadabra for me.

I am using Windows 8.1 Enterprise and Sophos Security and Control version 10.3.

Thanks,

Salamander