On windows 7.
I cannot figure out how to set a volume active or boot on a GPT disk with diskpart.
Is that the wrong tool?
I am having to go back to MBR, because I just can't figure out how to manage the disk when it is GPT.
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Since you talk about Windows, I'm guessing you'll be installing the system in UEFI mode.
GPT was designed for UEFI-style boot, which does not use such settings – instead the firmware itself keeps a list of boot entries corresponding to files in the EFI system partition, and integrates them into the regular "select boot disk" menu. For example, it could show something like:
UEFI Windows Boot Manager (\EFI\Boot\Microsoft\Bootmfgw.efi) UEFI Arch Linux (\EFI\systemd\systemd-bootx64.efi) BIOS Hard Disk 1 BIOS Floppy Disk
So instead of changing the "active partition" you would add a new entry through your firmware's settings screen (the "BIOS setup" one).
That said, GPT does have a similar "Legacy BIOS bootable" flag, which can be used when booting in BIOS mode. In the Linux
gdisk it can be set via
x (Expert) →
a (Attributes) → 2 (Legacy BIOS bootable).
However, since Windows 7 only boots from a GPT+UEFI disk or a MBR+BIOS one (not GPT+BIOS), you do not need to set it anyway. (For the same reason, I'm guessing that Microsoft saw no need to make it visible in DISKPART.)
Other bootloaders (e.g. GRUB or Syslinux) aren't necessarily as picky about mixing and matching boot configurations, and support BIOS booting from a GPT disk. But not all of them care about the "active" flag either – Syslinux uses it, but GRUB only cares about what's in