Booting from MDADM

When I try and set up grub to boot I get
grub> root (hd1,0)
Filesystem type unknown, partition type 0x83

So I added some partitions to /dev/hdc & /dev/hdd and tried

# mdadm --create --verbose /dev/md0 --level=0 --raid-devices=2 /dev/hdc1 /dev/hdd1

with which I was rewarded
# mdadm --create --verbose /dev/md0 --level=0 --raid-devices=2 /dev/hdc1 /dev/hdd1
mdadm: chunk size defaults to 64K
mdadm: Cannot open /dev/hdc1: Device or resource busy
mdadm: Cannot open /dev/hdd1: Device or resource busy
mdadm: create aborted

this guy http://togami.com/~warren/guides/remoteraidcrazies/
changed the parition type to fd so I'm gonna try that (and reboot)
and make p1 bootable

nope /dev/md0p1 didn't work.

It wants a partition table but can't see the one on md0p1
If I just mkfs on /dev/md0 grub can't see it cos there's no paritions.

I'm giving up on that and booting it from the 10Gb - though I plan to make it boot from CF eventually.