[gentoo-user] Copying data efficiently

Hi,

is there any tool in the Gentoo portage which may speed up (make it
mopre efficient) the following task:

On my HD there are data I want to copy to two identical external HDs.
These HDs are of the same type/model and each is separately
connectable via USB to my PC (...these two of the typical mobile external
USB-HDs).

Instead of copying the data twice from my PC to eah of the HDs I want
to do it once...like I would be able to give the cp-command two
instead of one target where to copy two.

The result should be two identically populated external HDs, each of
them useable/readable without the need to the other one.

What tool of the portage tree I able to accomplish this task?

Best regards,
mcc