• Method #1:

parted /dev/<devicename>

mktable
-> Table type: msdos
-> Destroy data: yes
-> quit

• Method #2:

fdisk -s /dev/<devicename> --- This gets the blocksize of the device.

Make the last five digits of this number zeros. Example: fdisk -s /dev/sda
Will show an error about GPT, and then the block size: 39078144
Change to 39000000 which equals our blockcount

dd if=/dev/zero of=/dev/devicename bs=1k seek=blockcount
dd if=/dev/zero of=/dev/devicename bs=1k count=20

• Method #3:

dd if=/dev/devicename of=/dev/zero bs=4k

• Method #4 (Clonezilla):

sgdisk -z /dev/sda