`yes` is far faster on my Linux (2.2GB/s) vs /dev/urandom (0.38GB/s) -- not surprising since the `man` page for urandom says:

"[urandom] is designed for security, not speed, and is poorly suited to generating large amounts of random data"

`cat /dev/zero` is pretty much as fast as `yes` on my system however (2.1GB/s)