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Migrate Linux to ZFS

Some steps I have followed to run Manjaro Linux from ZFS partition.

Backup system

Make a backup of the system for example with bsdtar command as described on Backups pages. One important thing is to make sure that system has installed linuxNN-zfs and zfs-utlis modules.

Create Manjaro Live CD with zfs support

More info: https://wiki.manjaro.org/index.php/Build_Manjaro_ISOs_with_buildiso

  1. Clone iso-profiles:

    git clone https://gitlab.manjaro.org/profiles-and-settings/iso-profiles.git ~/iso-profiles

  2. Add required components to manjaro/kde/Packages-Live (for me it was not enough to add it to Packages-Desktop, but to be sure add it there, too):

    KERNEL-zfs
zfs-utils
gparted

  3. Create iso with:

    buildiso -p -f kde

  4. Burn ISO to USB with:

    sudo dd bs=4M if=/var/cache/manjaro-tools/iso/manjaro/kde/<version</manjaro-kde-<version>.iso of=/dev/<usb-drive> status=progress oflag=sync

Install EFI boot loaders

Useful EFI boot loaders: rEFInd (to choose between Windows & Linux), ZFSBootMenu (to easily boot Linux from ZFS pool).

Partitions

Created partition with type = 0xBF00 (Solaris Root). To change partition type you can use fdisk. Solaris root partition type in fdisk is 156. You can add it a label, for example “Linux” for easier identification during filesystem import.

Create ZFS pool on the partition

sudo zpool create -f -o ashift=12 -o autotrim=on -O acltype=posixacl -O xattr=sa -O atime=off -O relatime=off -O recordsize=256k -O dnodesize=disabled -O normalization=formD -O mountpoint=none -O canmount=off -O devices=off -O compression=zstd-3 ssd /dev/disk/by-partlabel/Linux

Please note! As of 2023-11-11 I have found a bug in openzfs that dnodesize=auto makes it impossible to reveive incremental backup, so I changed it form auto to disabled. If you have it enabled you can still take care and set -o dnodesize=legacy during creating datasets. It’s enough to set it to the root dataset, as the children datasets will inherit the setting.

Create containers:

sudo zfs create -o canmount=off -o mountpoint=none ssd/manjaro

Create datasets

sudo zfs create -o canmount=noauto -o mountpoint=/ ssd/manjaro/root
sudo zfs create -o mountpoint=/home ssd/manjaro/home

Verify:

zfs list

Mount ZFS filesystems

sudo zfs umount -a
sudo zpool export ssd

sudo zpool import -d /dev/disk/by-partlabel/Linux -R /mnt ssd
sudo zfs mount ssd/manjaro/root

Copy system files

Update system configuration

Information to boot loaders where to find root file system:

sudo zpool set bootfs=ssd/manjaro/root ssd

Copy the zpool cache file:

sudo zpool set cachefile=/etc/zfs/zpool.cache ssd

sudo mkdir -p /mnt/etc/zfs
sudo cp /etc/zfs/zpool.cache /mnt/etc/zfs/zpool.cache

Chroot to the system:

sudo chroot /mnt

mount -t proc proc /proc
mount -t sysfs sys /sys
mount -t devtmpfs udev /dev

Edit /etc/mkinitcpio.conf file and add zfs to HOOKS before filesystems and move keyboard hook before zfs. If you are not using ext4 you can remove fsck, for example:

HOOKS=(base udev autodetect modconf block keyboard zfs filesystems)

Regenerate initramfs:

mkinitcpio -P

Comment out old root and home partitions from /etc/fstab.

Enable necessary services for automatically mounting zfs datasets:

sudo systemctl enable zfs.target
sudo systemctl enable zfs-import-cache
sudo systemctl enable zfs-mount
sudo systemctl enable zfs-import.target

Exit from chroot:

umount /dev
umount /sys
umount /proc
exit

Unexport ZFS pool

sudo zfs umount ssd/manjaro/root
sudo zpool export ssd

Reboot

Now the system should be bootable from ZFSBootMenu.

If after boot the filesystem is readonly, you can load it by adding rw to the kernel command line (CTRL+E in ZFSBootMenu). After the system is loaded you can set it as persistent with:

  • call cat /proc/cmdline to see what’s the current command line is, for example: zfs=ssd/manjaro/root nvidia-drm.modeset=1 spl.spl_hostid=0x00bab10c
  • call sudo zfs set org.zfsbootmenu:commandline="<OLD_COMMAND_LINE_WITHOUT_ZFS_PART> rw" ssd/manjaro/root, for example: sudo zfs set org.zfsbootmenu:commandline="nvidia-drm.modeset=1 spl.spl_hostid=0x00bab10c rw" ssd/manjaro/root

You can set this property on the parent dataset (ssd/manjaro) and inherit it for ssd/manjaro/root (please verify if the property is set for it, if it is just unset it with inherit command).