[root@nl54 ~]# mdadm --create /dev/md3 -v --raid-devices=2 --level=raid1 /dev/sdc1 /dev/sdd1 --assume-clean
mdadm: /dev/sdc1 appears to be part of a raid array:
    level=raid1 devices=2 ctime=Thu Feb 10 08:53:03 2011
mdadm: /dev/sdd1 appears to be part of a raid array:
    level=raid1 devices=2 ctime=Thu Feb 10 08:53:03 2011
mdadm: size set to 488383936K
Continue creating array? n
mdadm: create aborted.
[root@nl54 ~]# cat /proc/mdstat
Personalities : [raid1]
md2 : active raid1 sdb2[1] sda2[0]
      4192896 blocks [2/2] [UU]

md0 : active raid1 sdb3[1] sda3[0]
      475805056 blocks [2/2] [UU]

md1 : active raid1 sdb1[1] sda1[0]
      8385792 blocks [2/2] [UU]

unused devices: <none>