Removing GPT from a disk

The GUID Partition Table (GPT) is unique in that it resides both at the
beginning and the end of a disk. Its removal is not as simple as zeroing
out the first 512 (or 446) bytes.

For demonstration, I have a Seagate 750GB drive with a device name sdb

Figure out where to start zeroing

[root@livecd centos]# fdisk -s /dev/sdb  

This is the total number of blocks; we’ll zero out the last 100,000

dd if=/dev/zero of=/dev/sdb seek=732500000 bs=1k

Now zero out the first 1000 (overkill, really)

dd if=/dev/zero of=/dev/sdb count=1000 bs=1k

Ta da!