I recently bought a Synology disk array. I bought it because I also bought a new iMac with a 1TB solid state hard drive. I know this may sound ridiculous, but 1TB is not a lot of storage space. I have a music program that takes up approximately 200GB of storage and another graphics resources program that used to take up nearly 500GB of storage space. Add to that a 200GB iTunes Library and a bunch of applications and 1TB goes pretty quickly.
So, I moved all my files to the disk array. In addition to storing documents, the disk array can also stream my iTunes library to my Apple TV, iPhone, iPad, or any other device in any room in the house.
But, I also learned, the hard way, that disk arrays fail, so I'm backing up the entire array to Amazon's Glacier Service. This is a special service that is designed for archiving data. Because of the length of time it would take to get the data back from Amazon (unless I want to pay extra to get it quicker), the cost for storage is very low, currently one penny per gigabyte/month or $10 per terabyte/month.
For quicker restores I use Crash Plan. I like Crash Plan because you can backup external drives on Macs. Carbonite will back them up on the Windows platform, but not for Mac.
I also use Dropbox, ADrive, SkyDrive and Google Drive to store files - many redundantly. It may sound like overkill, but you just can't be too careful. The most important thing is to have a strategy for data loss because it will happen.