So why unRAID versus RAID 5?
For me, speed is not a major concern. Yea I need enough to stream movies around the network, sometimes more than 1 at a time, but for me getting every last bit of speed possible is not a real issue and not something that is going to make a real difference day in and day out. Sure large file transfers may take a bit longer, but how often am I sitting there waiting for the transfer to complete with noting else to do?
So the real issue for me was efficient protection (ie, parity drive), ability to use varying sized drives, easy expansion, ability to remove drive and read data from another system if ever needed, array not destroyed by multiple drive failures. Does this feature set sound familiar?
RAID 5 meets some of these but fails on others. unRAID meets all of these. So it was an easy decision and actually one I made prior to learning about DE being removed from WHS.