I work in data protection for IBM and practice what I preach at home. You need to think about what your disaster recovery scenario is going to look like. Let me explain...
For me, I have roughly 2TB of music, movies and docs. So I think "what am I protecting AGAINST? For me, it's accidental deletion, modification, corruption, or a server/drive failure. I have two home servers. One is a RAID10 built with 4TB drives. It offers protection at the DRIVE layer (meaning I can lose drives and be ok). I sync everything to another server downstairs that simply has two 2TB drives in it that receive the sync across my home network. I have it do this sync every night. There's logic built into it too so if the number of files changed exceeds X% it won't sync the changes (like in the event of a large scale deletion). Additionally, I have an offsite copy. For this, dropbox is pretty sweet. I use something called Boxifier to let me sync specific folders on the machine to Dropbox. Dropbox gives you a version history too that goes back 30 days (I think). For $10 per month, dropbox gives you 1TB which, for my music library and documents, is plenty. I don't include my movie library in the offsite backups. It's a huge amount of data and to be honest, if the house burns down, I'm not going to give a flying fuck what happened to my movies....just my documents and music.
Not sure exactly what your situation is but I agree with Zech that you should end up with a NAS device. Drobo and Synology make excellent devices and Qnap does too. Plex (a media server application) now has a version that runs on all of them so you can offload your media library streaming to that device. All newer NAS devices allow you to specify how you want things configured. Two things that are pretty cool though. Some of them allow you to also sync copies of your data out to the cloud. You simply put in your credentials for your Cloud Storage and it handles the rest. Lastly, RAID type (historically) had to be set/defined when you first setup the device. I know the Drobo has something called "Beyond RAID" which is a sort of dynamic RAID. As an example, maybe you start out with those 2x5TB drives in the beginning. It will operate as a RAID1 mirror. Later on you add another drive or two and it will dynamically expand and rebalance the volume across the new drives; even if they aren't the same size drive. Pretty nifty if you ask me.
