duplicating a disk

Gentlemen: I have a situation where I need to make a number of identical computers all with the same fedoraCore2. I have tried putting a second (hdb) disk, doing a "df" on hda and based on the number of 1024 blocks going: dd if=/dev/hda of=/dev/hdb bs=1024 count=<TheNumberDfShows> and it blinks the light a long time and then croaks. I know I did something similar to this a couple of years ago on a different project. Can someone tell me where I am going awry and perhaps educate me a little bit more. Signed, OldDogTryingToRememberNewTrick