DD is an extremly usefull tool for the seasoned and novice sys-admin here are some commands I have found usefull...
Create a file xKb in size containing random data.
dd if=/dev/urandom of=/tmp/my_random.dat bs=1kb count=10
Simple time command for testing disk rw
time dd if=/dev/zero of=/tmp/writetest.tmp bs=1M count=1024
