My father has assigned me the job of building him a server for storing and sharing all of his private documents. He needs the server that is 100% secure because he handles tons of his clients' sensitive information (he is an attorney). I can't use a cloud server because those are not secure enough. I'm thinking about a linux server running Tonido or BitTorrent Sync with a RAID 1 configuration and 1-2 TB of hard drive space. Are there any suggestions?
I would go straight for linux.
Could use NAS4Free, as long as you setup user perissions correctly it is nice and secure. If I remember corectly it's based off of BSD.
It uses normal samba for internal network stuff and has options to run a secure FTP server if external network connection is required.
RAID can be configured through software and also support for most hardware RAID controllers
I've used this guide to build my home server. The guide has a lot of focus om making the server secure. It should be perfect for you.
http://ubuntuforums.org/showthread.php?t=1895084
It's a lot to read. But if you really want to make sure you understand what you're doing and that you're doing it right it's a very good guide.
You will also have to find a guide on hot to set up Samba on it if you want to share files with Windows computers. It's not overly complicated (even though Windows is a pain to have to deal with ^^) and google should be able to help you with that no problem.
I would also suggest BitLocker
freebsd 100%