Disk setup

partitions, filesystems, UEFI+BIOS boot

What I wanted:

• a UEFI boot without a separate bootloader (i.e. bootstrap by the kernel EFISTUB loader)
• a backup BIOS boot with GRUB(2) just in case (it has proved useful a few times already)
• Btrfs (yeah, I will write about my backup scheme one day :D)

What I did not want:

• dualboot ;-)

By the way, my X1 Carbon has a 256GB SanDisk SD5SG2256G1052E SSD (and it’s blazing fast :P).

Partition Table

For UEFI boot, the GPT partition scheme is a good idea. Therefore one needs to use gdisk instead of fdisk to setup partitions.

Here is how I set up mine:

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048          264191   128.0 MiB   EF00  EFI System
   2          264192          266239   1024.0 KiB  EF02  BIOS boot partition
   3          266240       482611199   230.0 GiB   8300  Linux filesystem
   4       482611200       500118158   8.3 GiB     8200  Linux swap

sda1 is the EFI boot partition (type EF00) and sda2 the BIOS/GRUB one (see below for the boot setup), sda4 is swap (so large because I want to use hibernation), and all the remaining space went to sda3, which was then set up as a Btrfs raw storage pool.

EFI + BIOS Boot

EFI

First of all, reading ArchWiki’s articles on UEFI and UEFI bootloaders or something comparably useful is sort of required in order to figure out what I am talking about here. I just provide a quick summary of what I did, not a thorough explanation of all the UEFI stuff.

When booting in EFI mode, I use the EFISTUB bootloader built into the kernel (stock Arch kernels have had it compiled in since fall 2012). This means that it “Just Works” (unless it doesn’t). The ArchWiki recommends using rEFInd to get a nice menu and set the kernel commandline parameters, but I have decided to bake the commandline into the firmware and boot the kernel directly instead.¹

To edit the EFI boot menu, one needs to boot in EFI mode². Then I modprobe’d efivars and used efibootmgr to add the boot menu entry (including the kernel commandline, since I have no intermediate bootstrapping something in between the kernel and the firmware).

Note for the future me: this is the efibootmgr command:

efibootmgr -c -g -d /dev/sda -p1 -L ArchLinux -l "\EFI\arch\vmlinuz-linux.efi" -u "`cat /boot/efi/EFI/arch/linux.conf`"

(Note for the past me: Thanks! :D)

I also added an EFI shell just in case. It was a good idea :P

A side note: If a new kernel is installed but does not get copied into /boot/efi, it will not boot and there will be no error message. Therefore, this (or other methods listed there) is a great idea.

BIOS+GRUB

I somehow installed GRUB2 onto the BIOS boot partition (sda2 in my case), and it somehow works – the computer happily boots with GRUB in BIOS mode and with EFISTUB in UEFI mode. Unfortunately I can’t remember the details of how exactly I got it to work. But that probably signifies that it wasn’t hard, so it might actually be a good thing O:-)

linux.conf in the same directory as the kernel image instead of from the boot menu in the firmware, but this works for me, too.

create an EFI-capable liveUSB first.

Filesystem

My whole system besides /boot/{EFI,GRUB} resides on one btrfs partition, with different subvolumes for /, /home and /var. With the awesome snapshot capabilities of btrfs, this allows for neat rollback in case an update breaks something, makes online backup terribly simple and just generally rocks.³

I chose LZO compression, as some benchmark out there claimed btrfs with LZO was the fastest option on SSDs similar to mine. I might run my own benchmarks one day.

Here is my /etc/fstab:

# <file system> <dir>     <type>  <options>                                                 <dump> <pass>

LABEL=btr       /         btrfs   rw,noatime,ssd,space_cache,compress=lzo,subvol=root       0 1
LABEL=btr       /var      btrfs   rw,noatime,ssd,space_cache,compress=lzo,subvol=var        0 2
LABEL=btr       /home     btrfs   rw,noatime,ssd,space_cache,compress=lzo,subvol=home       0 2
tmpfs           /tmp      tmpfs   nodev,nosuid,size=5G                                      0 0
LABEL=swap      none      swap    defaults                                                  0 0

LABEL=btr       /btrroot  btrfs   noauto,rw,noatime,ssd,space_cache,compress=lzo,subvolid=0 0 2

UUID=4ECD-9824  /boot/efi vfat    rw,noatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro 0 2