If you're really doing video, I suspect you'd use storage arrays (perhaps arrays of SSD for high-end) instead of trying to cram it into your workstation, not to mention you'd want redundancy (and sharing) for production-type work

A lot of editors will keep all of their footage on some form of networked storage until they need to work on a specific piece of it. Bring it to the machine, edit it, and send it back to the storage array.