Not the cheapest, but I've used a Drobo for several years. Can be picked up secondhand on the bay for decent money.
Beauty with these is that they automatically back up your files between the hard drives, so if you do lose a drive, no music is lost, and you can hot swap drives again with no loss of data.
Great bit of kit and just works, no need to faff about setting up RAID or similar.
“Music has always been a matter of energy to me, a question of fuel. Sentimental people call it inspiration, but what they really mean is fuel. I have always needed fuel. I am a serious consumer. On some nights I still believe that a car with the gas needle on empty can run about fifty more miles if you have the right music very loud on the radio”
Hunter S Thompson