Solved GPT disk on legacy BIOS

Ekynox360

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Messages: 4

Hello everyone!

I'm wondering if it's possible to install FreeBSD 12.0 on a GPT disk but on a server whose firmware is not UEFI. I found this thread that says it's possible. Can you confirm this or even add more details?

Thx
 

mickey

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I'm wondering if it's possible to install FreeBSD 12.0 on a GPT disk but on a server whose firmware is not UEFI. I found this thread that says it's possible. Can you confirm this or even add more details?
Yes it's possible. I have been using GPT disks on machines that only have legacy BIOS without any problems.
You will need a GPT partition of type freebsd-boot that holds either /boot/gptboot or /boot/gptzfsboot depending on whether you will be using UFS or ZFS for your root partition to boot from. According to gpart(8), the freebsd-boot partition should be smaller than 545 KB. I would also advise to create a GPT partition of type freebsd-swap for use as swapspace. The data partition where FreeBSD gets installed either is of type freebsd-ufs or freebsd-zfs repectively. It's probably a good idea to also create a GPT partition of type efi as the first partition on the disk, even though a BIOS system will not make use of it, but it saves you the hassle should you later upgrade to a UEFI capable mainboard.

An example disk layout for ZFS could look something like this:
Code:
1    efi             (256M)
2    freebsd-boot    (512K)
3    freebsd-swap    (8G)
4    freebsd-zfs     (remainder)
 
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Ekynox360

Ekynox360

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Messages: 4

You will need a GPT partition of type freebsd-boot that holds either /boot/gptboot or /boot/gptzfsboot depending on whether you will be using UFS or ZFS for your root partition to boot from.
freebsd-boot is automatically created by using GPT auto partitioning. Thank you for your clear answer :)
 

SirDice

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a GPT disk but on a server whose firmware is not UEFI
UEFI is not a requirement to be able to use GPT. Most older BIOS booting machines will be able to deal with GPT thanks to the way the PMBR works. That said, some really old machines can have difficulty with it though, they usually don't like the "fake" MBR partition that GPT creates. Whether or not GPT will work really depends on how "old" that machine actually is.

It's probably a good idea to also create a GPT partition of type efi as the first partition on the disk, even though a BIOS system will not make use of it, but it saves you the hassle should you later upgrade to a UEFI capable mainboard.
The installer allows you to choose between GPT-CSM, GPT-UEFI or a combination GPT-CSM+UEFI. The combination creates both freebsd-boot and efi partitions allowing you to switch back and forth between UEFI and CSM boot.


I found this thread that says it's possible.
Different issue. The original question basically wanted to CSM boot the machine and use UEFI features. That's not possible, it's one or the other, not both. It had nothing to do with GPT.
 
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