Passphraseless Disk Encryption Options?

[Wojciech Puchar]

> I?m trying to perform a whole disk encryption for my boot drive to protect its data at rest. However I would like to have a mac OS X-ish full disk encryption that does not explicitly ask for a passphrase and would boot as normal without manual input of passphrase. I tried to do it with geli(8) but it seems there is no way I can avoid the manual interaction. Really curious if there is a way to achieve it? Thanks!

what's a point of encrypting your disk if passphrase don't need to be 
entered. Where is a security?