Can partitions span more than one drive?

[John Almberg]

Now that I've got my rsnapshot backup server working beautifully,  
backing up several servers to a central backup server (I like this a  
lot), I have a problem...

I built my backup server from a machine I had lying around. It has  
two 140G hard drives. I dedicated one drive to a /backup partition.  
Unfortunately, that is now running at 88% capacity... i.e., only 16G  
left...

Now that I know this approach is going to work, I'm going to run out  
and buy a big drive.

Question: is it possible to just expand my existing /backup partition  
to encompass both the current drive and the new drive? I'm guessing  
not, since Chapter 8 in "Absolute FreeBSD" says that a partition is  
part of a slice, which is part of a physical drive, but maybe some  
bright person has come up with an app that overcomes that limitation.

Thanks: John