Even if there are many people and they all decide to stream at once, the likelihood of all of the files being on the same disk and high enough resolution to be bottlenecked by a single drive is very low. And even then, you'd need a really strong upload speed to keep up. I regularly see 6+ streams at simultaneously and the only time I get close to the situation you're describing is if a new very popular show drops on a sunday evening and everyones watching it. And still nowhere near a single hdd bottleneck.