http://serverfault.com/questions/488346/removing-raid-metadata-from-drives

http://www.server-world.info/en/note?os=CentOS_6&p=raid_metadata

If you are reusing disk drives that were once members of a RAID array, you should remove the RAID metadata from the disk drives first.

1. Configure the SATA in the host BIOS to RAID mode
2. Enter the RAID configuration (Control-I)
3. Delete the RAID volumes
4. If the RAID configuration (metadata) is 'messed up'
   1. Recreate a RAID volume
   2. Reboot and go back into the RAID configuration (Control-I) again
   3. Delete the RAID volume just created
   4. Reboot again

Where x is the drive you want to remove the RAID metadata from:

mdadm --zero-superblock /dev/sdx

or:

dmraid -r -E /dev/sdx

or:

dd if=/dev/zero of=$YOUR_DEV bs=512 seek=$(( $(blockdev --getsz $YOUR_DEV) - 1024 )) count=1024

Then verify:

You may need to reboot!

dmraid -r

or

mdadm --detail --scan --verbose