Installing Centos you can see some error like: Disk contains BIOS metadata, but is not part of any recognized BIOS RAID sets. Ignoring disk sdb

dmraid -r -E /dev/sda

if this not helps so:

mdadm –zero-superblock /dev/sda

Hard way:

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