>didn't know people kept porn on their HDD
You are kidding me.
>awkward if someone found your HDD and went through it
If you live with people, you can somewhat confidently guess that they will respect your privacy and not look through your stuff.
Even if they did look through it then so what? It then that they did that. They should at least tell you they look through your stuff and tell you if they deleted or modified anything in your drive. Just don't keep any illegal porn on your HDD unencrypted, especially if you live in a country where lots of types of porn are illegal (maybe like Afghanistan or somewhere).