I think that the parent thought that the system had to use a single SSD. The first time I read the question I thought that I had to use the hard drive that the data came on, and that it was all I was allowed to use. I didn't realize that the point was to design a system to simply serve the data that was given to us. After reading it, it becomes pretty clear that a simple raid5 with a few SSD's makes this problem moot.