OpenBSD is the most pleasing expérience I’ve had with an OS. It’s fully contained and has all the tools you need without needing to install anything (eg a DNS, HTTP, SMTP servers, a proxy, a good firewall). All config files look alike and use the same keywords for the same things, making it straightforward to configure everything.

And regarding RAID 1, I’ve never done it myself, but it totally works out of the box (as well as full disk encryption).