I use "yes > file" to benchmark IO, knowing that this is pretty much the "speed of light" for writes. I could use "cp /dev/urandom file" but then it's hard to

I use "yes > file" to benchmark IO, knowing that this is pretty much the "speed of light" for writes. I could use "cp /dev/urandom file" but then it's hard to tell if the filesystem or kernel optimize a copy different from generating your own writes.