Mdadm issue

This is the first time I am setting up raid using the mdadm tool. This
is what I am trying to do. 

The sever is as follows: 2 drives at 10gig
                         2 drives at 80gig
hda2 is /
hdd1 is my /home

I have the other drives in ad ready and would like to set up the 2 10
gig's as a mirror and the 2 80 gig as raid0

At the shell I run this command 

mdadm --create /dev/md0  --level=1 --raid-disks=2 /dev/hda2 /dev/hdb1
and get the following output:

mdadm: /dev/hda2 appears to contain an ext2fs file system
    size=7269412K  mtime=Mon Jul  1 11:56:16 2002
mdadm: /dev/hdb1 appears to contain an ext2fs file system
    size=7333640K  mtime=Mon Jul  1 11:56:29 2002
Continue creating array? y
mdadm: SET_ARRAY_INFO failed for /dev/md0: File exists

Could someone please help me with this problem. I am having a really
hard time finding any info on the web about this.