Solution: dd too slow on Mac OS X

When I was cloning SD cards on Mac OS X using dd', it takes ages to get things done. I was using the following command:

It takes much less time when using /dev/rdisk2 instead of /dev/disk2:

The reason is that rdisks are "raw" thus resulting in a higher R/W speed, according to man hdiutil` [1]:

/dev/rdisk nodes are character-special devices, but are “raw” in the BSD sense and force block-aligned I/O. They are closer to the physical disk than the buffer cache. /dev/disk┬ánodes, on the other hand, are buffered block-special devices and are used primarily by the kernel’s filesystem code.

[1] http://superuser.com/questions/631592/mac-osx-why-is-dev-rdisk-20-times-faster-than-dev-disk