[NTLUG:Discuss] backing up a full disk image to external disk

[Ed Leach]

What is the best way to backup a full disk image to an external hard 
disk that is bigger than the disk being backed up?

On my desktop I have two identical internal hard disks. I just boot to a 
live distro and do a dd from one to the other.

This time I need to backup an 80 gig laptop hard disk to an external 120 
gig disk. Do I create an 80 gig partition on the external disk and then 
do something like:

   dd if=/dev/sda of=/dev/sdb1

I think there is a better way but don't know what it is.

Thanks,

Ed