I had to make a bootable USB under OS X. To my great surprise, I found that the copy speed with DD is disgustingly low ~ 600KB / s 😕 . After a short search I found, that I should use rdiskX instead of diskX. The idea is that rdisk is synonymous with raw device. So far, I immediately added an r to the block device to which I copied the ISO and then found that the speed is even lower ~ 150-200KB / s 😡 . The mystique is now complete and previous information has been confirmed by many sources!!!! Everything fell into place after I put the bs directive.
bs=n Set both input and output block size to n bytes, superseding the ibs and obs operands. If no conversion values other than noerror, notrunc or sync are specified, then
each input block is copied to the output as a single block without any aggregation of short blocks.
After I put 1M for the size of bs I achieved the speeds I expected from my USB. Then I tested and the difference between disk and rdisk definitely the difference was about 10-12 times in speed in favor of rdisk. A very cultural way to monitor the speed and progress of dd can be achieved with the following pipeline
sudo dd if=Downloads/path.to.iso bs=1M | pv | sudo dd of=/dev/rdisk2 bs=1M