I'm using CentOS 5. I've created a partition on each of two different hard disks with parted. They are of the same size and of type "fd". Both parted and fdisk confirm they are raid devices.

But when I try to create a RAID device like this:

mdadm --create --auto=yes --level=1 --raid-devices=2 /dev/sda4 /dev/sdb2

I get the message "You haven't given enough devices to create this array"

Then I check the partitions:

mdadm -E /dev/sdb2

and for each of them I get the message "No md superblock detected".

Why is their no md superblock? I've tried creating the partitions with fdisk, but same result. I have also rebooted after creating the partitions and still get this result.

What step am I missing in creating these partitions?

Thanks

raid 5 must have a minimum of 3 devices.

I'm making this RAID 1.