1. Check meta information:

[root@dlp ~]# dmraid -r
/dev/sdb: ddf1, ".ddf1_disks", GROUP, ok, 124914352 sectors, data@ 0

2. Delete meta information:

[root@dlp ~]# mdadm --zero-superblock /dev/sdb
[root@dlp ~]# dmraid -r
no raid disks and with names: "/dev/sdb"

3. If it not help, delete all from hard disk:

[root@dlp ~]# dd if=/dev/zero of=/dev/sdb bs=512 seek=124914352
[root@dlp ~]# dmraid -r
no raid disks and with names: "/dev/sdb"

Seek parameter you can see by:

blockdev --getsz /dev/sdb