UEFI Big Drive question

[Chris Murphy]

On May 9, 2014, at 6:05 PM, Stephen Morris <samorris at netspace.net.au> wrote:

> The one limitation with GPT as I understand it is that in order to use GPT you must also have UEFI active in the Bios.

No. First, BIOS ≠ UEFI they are not the same thing and it's easy to remember because there's nothing basic about UEFI. Second, while it's true GPT is defined in the UEFI spec, it's entirely up to the BIOS firmware implementation whether it'll work. There's no blanket proscription using GPT on BIOS computers, I have an old Dell Latitude laptop that permits booting with GPT partitioned drives.

But there are enough firmwares out there that crater when encountering some aspect of GPT partitions, that on BIOS computers, the Fedora installer doesn't use GPT by default unless the drive is larger than ~2.2TB.

>    From experience I have also found that you can't install the windows system partition on a GPT device and I thought I read somewhere that you also can't put Linux /boot on GPT either.

The first part is true, the second part is not true. Windows' installer will only install and boot from GPT drives on UEFI computers, and boot from MBR drives on BIOS computers. Neither Linux nor GRUB nor any other bootloader I'm aware of, cares if your BIOS computer uses GPT partitioning. It's just a matter of whether the firmware is fussy about it or not.

Quite a few BIOS firmwares don't like the standard GPT because its protective MBR 0xEE entry doesn't have the active bit (boot flag) set. So via parted, anaconda will set this flag even on GPT disks, and this tricks many BIOS firmwares into cooperating. But it causes problems with others, usually UEFI firmware, because strictly speaking 0xEE shouldn't be set as bootable. Anyway it takes testing to know whether it'll work or not.


Chris Murphy