Solution: dd too slow on Mac OS X

Does your dd command seem to be far too slow on your MAC?
It is not the dd command that makes it slow, it's the device that you selected.
On a MAC there exist for an external attached USB device two names in the /dev/ tree (example):

/dev/disk3

and

/dev/rdisk3

If you copy from /dev/disk3 with dd command (does not depend much on the blocksize that you
selected) then you will get around 30Mbytes/s. Now if you choose /dev/rdisk3 then you can
get up to 300Mbytes/s (using a USB3.0 SATA adapter and a fast disk of course).

Thanks to Daoyluan Li (http://daoyuan.li/solution-dd-too-slow-on-mac-os-x/#comment-13896)
who found that solution!!!