[Solved] Arch + W8 dual boot, UEFI, partitioning question

Question

Hello,
I'm buying new laptop with preinstalled W8 (Lenovo E430) and I'm planning to dual boot. I've read Beginner's guide, Installation guide, searched forum, etc., but I'm still unsure how to deal with creating partitions for Arch while keeping Windows.
From the Beginners' Guide:
If you are intending to follow the advice to create a GPT partition table then you need to choose "Advanced" and then select "gpt" from the drop-down menu. This cannot be done if you have a pre-existing Windows installation on the drive which you wish not to destroy.
and from the Partitioning:
To dual-boot with Windows, one must use MBR.
A special exception to this rule: dual-booting Windows 64-bit using UEFI instead of BIOS, one must use GPT.
My W8 will be 64bit and also is Arch.
So, my question is. When I shrink W8 partition and create free space for Arch, do I have to choose 'gpt' option (2nd quote) or not (1st quote) for formatting? Or am I reading it totally wrong?
I would give it a try, but that destroying thing kind of scares me.
Last edited by centos (2013-06-18 19:24:58)

Answer 1

The wiki quotes you've presented make it look like the wiki was created with an MBR/BIOS assumption and then poorly edited to incorporate GPT/EFI information. The rules, presented in a more cohesive way, are these:
Windows ties its partition table type to the computer's firmware: under BIOS, Windows requires MBR; and under EFI, Windows requires GPT.
Linux is more flexible: It can use either MBR or GPT under BIOS. In theory, Linux can use either MBR or GPT under EFI, although many EFIs seem to require GPT, so it's best to stick with GPT on EFI-based computers.
When dual-booting, Windows is the limiting factor when it comes to partition table type.
Most EFIs include a Compatibility Support Module (CSM), which enables them to boot BIOS-based OSes. The CSM can usually be enabled or disabled in the firmware setup utility, although the details of how to do this vary from one implementation to another.
Computers that ship with Windows 8 pre-installed almost always use EFI, and therefore GPT.
Converting from MBR to GPT or vice-versa is possible with GPT fdisk (gdisk, cgdisk, or sgdisk), but this requires re-installing the boot loader for any already-installed OS(es). If Windows is one of those OS(es), it's probably not worth the effort.
GParted and parted can convert from MBR to GPT or vice-versa only by destroying existing partition entries, so you should use these tools to make such a change only on a blank disk or if you intend to lose all the existing partitions.
Since you (centos) say you're installing to a computer with a pre-installed Windows 8, you've almost certainly already got an EFI/GPT setup. Under these circumstances, you won't be choosing a partition table type unless you want to completely wipe that installation and install both OSes fresh. GParted will detect the partition table type and work with it automatically; you should not select the option to create a new partition table, which your first quote (partially) describes. You should, however, be sure that you install Arch in EFI mode and that you install an EFI-mode boot manager and/or boot loader, rather than a BIOS-mode version of GRUB. Getting an EFI-mode Windows and a BIOS-mode Linux to coexist is possible, but awkward. Converting a BIOS-mode Linux installation to boot in EFI mode is also possible, if you mistakenly install in BIOS mode; but it's usually easier to install in EFI mode to begin with. There are lots of threads here on EFI-mode Arch installations, as well as information in the Arch wiki on this topic. Unfortunately, EFI is still new enough that there are still a lot of kinks to be worked out, both in specific firmware implementations (many of them are buggy) and in OS support (which is still not as mature as is BIOS support).