Installing Arch Linux on ZFS

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The Zettabyte File System (ZFS) is an advanced copy-on-write filesystem designed to preserve data integrity from a multitude of possible corruption scenarios as well as provide simple administration features. ZFS makes disk administration effortless with support ZFS storage pools (zpools) and automatic mount handling. First released in 2005 for Solaris OS, ZFS has since become the flag bearer for next generation filesystems.

ZFS was first developed and released by Sun (now owned by Oracle) as Open Source Software licensed under the Common Development and Distribution License (CDDL) which is famously incompatible with the GNU Public License. This incompatibility prevents ZFS from being merged into the mainline kernel, and generally presents some obstacles for users that want to use ZFS in Linux. is a project funded by the Lawrence Livermore National Laboratory to develop a native Linux kernel module for its massive storage requirements and super computers.

Notes before installation

  • The ZFS packages are tied to the kernel version they were built against. This means it will not be possible to perform kernel updates until new packages (or package sources) are released by the ZFS package maintainer.

Boot from the installation media

It is a good idea make an installation media with the needed software included. Otherwise, you will need the latest archiso installation media burned to a CD or a USB key.

To embed zfs in the archiso, from an existing install, download the archiso package.

# pacman -S archiso

Start the process:

# cp -r /usr/share/archiso/configs/releng /root/media

Edit the packages.x86_64 file adding those lines:


Edit the pacman.conf file adding those lines (TODO, correctly embed keys in the installation media?):

SigLevel = Never
Server =$repo/$arch

Add other packages in packages.both, packages.i686, or packages.x86_64 if needed and create the image.

# ./ -v

The image will be in the /root/media/out directory.

More informations about the process can be read in this guide or in the Archiso article.

If you are installing onto a UEFI system, see Unified Extensible Firmware Interface#Create UEFI bootable USB from ISO for creating UEFI compatible installation media.

Setup pacman

Activate the required network connection and then edit /etc/pacman.d/mirrorlist and configure the mirrors for pacman to use. Once that is done, edit /etc/pacman.conf and add the archzfs repository:

# nano /etc/pacman.conf
Server =$repo/$arch
Note: You should change the repo name from 'demz-repo-core' to 'demz-repo-archiso' if you are using the standard Arch ISOs to install (didn't build your own, above)

Next, add the archzfs maintainer's PGP key to the local trust:

   # pacman-key -r 0EE7A126
   # pacman-key --lsign-key 0EE7A126

Finally, update the pacman databases,

   # pacman -Syy

Install needed packages

This is also the best time to install your favorite text editor, otherwise nano will have to be used.

   # pacman -S archzfs dosfstools gptfdisk vim

Partition the destination drive

UEFI systems

Use the cgdisk partition utility and create a GPT partition table:

  Part     Size   Type
  ====     =====  =============
     1     512M   EFI (ef00)
     2     512M   Ext4 (8300)
     2     XXXG   Solaris Root (bf00)
Note: The EFI partion will be formatted to FAT32 and contain the UEFI boot loader. The Ext4 partition will contain the boot partition and kernel images.
Note: The filesystem type codes for cgdisk are indicated in the parenthesis after the filesystem name.
Warning: The EFI partition must be at least 512MB specified by the UEFI standard.

BIOS systems

  Part     Size   Type
  ====     =====  =============
     2     1007K  BIOS Boot Partition (ef02)
     1     512M   Ext4 (8300)
     3     XXXG   Solaris Root (bf00)
Note: You will have to create the ext4 partition first due to cgdisk's disk alignment policies. Start it at sector 2048 to leave room for the BIOS parition.

Format the destination disk

UEFI systems

Format the EFI partition to FAT32

   mkfs.vfat -F 32 /dev/sda1 -n EFIBOOT

Format the Ext4 boot partition

   mkfs.ext4 /dev/sda2 -L BOOT

BIOS systems

Format the Ext4 boot partition

   mkfs.ext4 /dev/sda1 -L BOOT
Note: The boot filesystem is sda1 because of the order we created the partitions

The BIOS partition does not need a filesystem.

Setup the ZFS filesystem

First, make sure the ZFS modules are loaded,

   # modprobe zfs

Create the root zpool

   # zpool create zroot /dev/disk/by-id/<id-to-partition>
Warning: Always use id names when working with ZFS, otherwise import errors will occur.

Create necessary filesystems

If so desired, sub-filesystem mount points such as /home and /root can be created with the following commands:

   # zfs create zroot/home
   # zfs create zroot/root

Swap partition

ZFS does not allow to use swapfiles, but you can use a ZFS volume as swap partition. It is importart to set the ZVOL block size to match the system page size, for x86_64 systems that is 4k.

Create a 8gb zfs volume:

 # zfs create -V 8gb -b 4K <pool>/swap

Prepare it as swap partition:

 # mkswap /dev/zvol/<pool>/swap

Enable swap:

 # swapon /dev/zvol/<pool>/maindisk/swap

To make it permament you need to edit your /mnt/etc/fstab after pacstraping the system:

Add a line to /mnt/etc/fstab:

 /dev/zvol/<pool>/swap none swap defaults 0 0

For safety, unmount all zfs filesystems if they are mounted:

   # zfs umount -a

Configure the root filesystem

Now it is time to set the mount point of the root filesystem:

   # zfs set mountpoint=/ zroot

and optionally, any sub-filesystems:

   # zfs set mountpoint=/home zroot/home
   # zfs set mountpoint=/root zroot/root

Set the bootfs property on the descendant root filesystem so the boot loader knows where to find the operating system.

   # zpool set bootfs=zroot zroot

Export the pool,

   # zpool export zroot
Warning: Don't skip this, otherwise you will be required to use -f when importing your pools. This unloads the imported pool.

Finally, re-import the pool,

   # zpool import -d /dev/disk/by-id -R /mnt zroot
Note: "-d" is not the actual device id, but the /dev/by-id directory containing the symlinks.

If there is an error in this step, you can export the pool to redo the command. The ZFS filesystem is now ready to use.

Mount the boot partitions

UEFI systems

   # mkdir /mnt/boot
   # mount /dev/sda2 /mnt/boot
   # mkdir /mnt/boot/efi
   # mount /dev/sda1 /mnt/boot/efi

BIOS systems

   # mkdir /mnt/boot
   # mount /dev/sda1 /mnt/boot

Install and configure the Arch Linux installation

Install the base packages

   # pacstrap -i /mnt base base-devel
   The other packages will be installed in the chrooted environment

Generate the fstab,

   # genfstab -U -p /mnt | grep boot >> /mnt/etc/fstab
Note: ZFS auto mounts its own partitions, so we do not need ZFS partitions in fstab file.

If installing on a UEFI system, you will need to load the efivars kernel module before chrooting into the installation:

   # modprobe efivars

Chroot into the installation

   # arch-chroot /mnt /bin/bash

Next, follow the Beginners' Guide from the "Locale" section to the "Configure Pacman Section". Once done, edit pacman.conf, add the archzfs repository, and update the pacman database,

   # pacman -Syy
   # pacman -Su --ignore filesystem,bash
   # pacman -S bash
   # pacman -Su
   Now lets install the other needed packages.
   # pacman -S gnupg vim

Re-create the initramfs, edit /etc/mkinitcpio.conf and add zfs before filesystems. Also, move keyboard hook before zfs so you can type in console if something goes wrong. Remove fsck and then regenerate the initramfs:

   # mkinitcpio -p linux

Finally, set root password and add a regular user.

Setup the bootloader

UEFI systems

Use EFISTUB and rEFInd for the UEFI boot loader. See Beginners' Guide#For UEFI motherboards. The kernel parameters in refind_linux.conf for zfs should include "zfs=bootfs", or "zfs=zroot", so the system can boot from ZFS. The 'root' and 'rootfstype' parameters aren't needed.

BIOS systems

Follow the Grub2#BIOS_systems_2 wiki. grub-mkconfig fails for me, so I edited grub.cfg manually.

set timeout=2
set default=0

# (0) Arch Linux
menuentry "Arch Linux" {
    set root=(hd0,1)
    linux /vmlinuz-linux zfs=zroot
    initrd /initramfs-linux.img

Unmount and restart

This is it, we are done!

   # exit
   # umount /mnt/boot
   # zfs umount -a
   # zpool export zroot
   # reboot
Warning: If you do not properly export the zpool, the pool will refuse to import in the ramdisk environment and you will be stuck at the busybox terminal.


If the new installation does not boot because the zpool cannot be imported, you will need to chroot into the installation and properly export the zpool. See ZFS#Emergency chroot repair with archzfs.

Once inside the chroot environment, load the ZFS module and force import the zpool,

   # zpool import -a -f

now export the pool:

   # zpool export <pool>

To see your available pools, use,

   # zpool status

It is necessary to export a pool because of the way ZFS uses the hostid to track the system the zpool was created on. The hostid is generated partly based on your network setup. During the installation in the archiso your network configuration could be different generating a different hostid than the one contained in your new installation. Once the zfs filesystem is exported and then re-imported in the new installation, the hostid is reset. See Re: Howto zpool import/export automatically? - msg#00227.

If ZFS complains about "pool may be in use" after every reboot, you should properly export pool as described above, and then rebuild ramdisk in normally booted system:

   # mkinitcpio -p linux

See also