I am trying to semi-securely erase a bunch of hard drives. The following is working at 20-50Mb/s

dd if=/dev/zero of=/dev/sda

But

dd if=/dev/random of=/dev/sda 

seems not to work. Also when I type

dd if=/dev/random of=stdout

It only gives me a few bytes regardless of what I pass it for bs= and count=

Am I using /dev/random wrong? What other info should I look for to move this troubleshooting forward? Is there some other way to do this with a script or something like

makeMyLifeEasy | dd if=stdin of=/dev/sda

Or something like that...