Most big data is videos, photo and audio which are played sequentially or in big enough chunks like one photo at the time that random access times and IOPS don't matter, a defragged hard drive is simply perfect for the task.
Err, no. Depends on what kind of video you're doing. In the video world it's easy to end up bottlenecked by disk I/O.
HD resolution ProRes files for instance will tax any hard drive, requiring over 40MB/s (330mbs) throughput:
I'm working with 4K sources, of which some are uncompressed. You need RAID or SSD.