http://www.newegg.com/Product/Product.aspx?Item=N82E16822145472
3TB HDD
Honestly if you have 10TB+ worth of files you want to keep in storage, I suggest getting an EXTERNAL drive. The number of ports and space available on the motherboard/case is limited. Also if you have 10TB+ worth of movies, TV shows, music, etc. wouldn't you want to be able to move it around. Maybe to a bigger TV in the house, or a friend's house, etc.
There are very small box-like computers that JUST house hard drives in RAID format. They can pretty much get as big as 15-20TB+.
For example
http://www.newegg.com/Product/Product.aspx?Item=N82E16822165287
Is a 6TB external hard drive cage with USB 3.0 support. When you want to watch your shows on your computer just hook it up to your tower. If you want to download things and move it to a big screen or a friend's house, just take the cage and connect it wherever.
20TB of space INTERNALLY is just a waste of space imo. Rather just keep internal hard drives small + performance.
EDIT: haha just saw this ad after I left this topic.
http://www.droboworks.com/?source=GRM&gclid=CIvBg_24iakCFQQ-bAodwmckpg
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