If GRUB is already installed on the system, review the GRUB section before installing PC-BSD® in order to determine which version of GRUB is installed. Legacy GRUB does not support GPT or ZFS. Depending upon your hardware, the installer may automatically select GPT or ZFS for you. You will need to change your layout to UFS and make sure that the "Partition disk with GPT" checkbox is unchecked while in the Disk Selection Screen of the installer. If GRUB version 2 is installed, you can select the installer's default partitioning layout as GRUB version 2 supports all of the disk options available during a PC-BSD® installation.