Making up for slow hdd speeds was kind of the major reason Hadoop was invented: if you spread your data around 100 of slow disks and then run MapReduce job that

Making up for slow hdd speeds was kind of the major reason Hadoop was invented: if you spread your data around 100 of slow disks and then run MapReduce job that reads from all 100 of them simultaneously then you effectively get 100x read speed. Plus, with rise of Spark which processes data primarily in RAM you can say that disk speeds are not really an issue for Big Data.